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Americans with Disabilities Act of 1990 | Lobbying | Lobbying
Over the years, key activists and advocates played an important role in lobbying members of the U.S. Congress to develop and pass the ADA, including Justin Whitlock Dart Jr., Patrisha Wright and others.
Wright is known as "the General" for her work in coordinating the campaign to enact the ADA. She is widely considered the main force behind the campaign lobbying for the ADA. |
Americans with Disabilities Act of 1990 | Support and opposition | Support and opposition |
Americans with Disabilities Act of 1990 | Support | Support
Senator Bob Dole was a supporter and advocate for the bill. |
Americans with Disabilities Act of 1990 | Opposition from religious groups | Opposition from religious groups
Conservative evangelicals opposed the ADA because the legislation protected individuals with HIV, which they associated with homosexuality.
The debate over the Americans with Disabilities Act led some religious groups to take opposite positions.Lawton, K.A. Christianity Today, 10/8/90, Vol. 34 Issue 14, p. 71 The Association of Christian Schools International opposed the ADA in its original form,"Should the Senate Approve the Americans with Disabilities Act of 1989?" Congressional Digest December (1989): 297 primarily because the ADA labeled religious institutions "public accommodations" and thus would have required churches to make costly structural changes to ensure access for all. The cost argument advanced by ACSI and others prevailed in keeping religious institutions from being labeled as "public accommodations". Church groups such as the National Association of Evangelicals testified against the ADA's Title I employment provisions on grounds of religious liberty. The NAE believed the regulation of the internal employment of churches was "... an improper intrusion [of] the federal government." |
Americans with Disabilities Act of 1990 | Opposition from business interests | Opposition from business interests
Many companies, corporations, and business groups opposed the Americans with Disabilities Act, arguing that the legislation would impose costs on businesses. Testifying before Congress, Greyhound Bus Lines stated that the act had the potential to "deprive millions of people of affordable intercity public transportation and thousands of rural communities of their only link to the outside world." The US Chamber of Commerce argued that the costs of the ADA would be "enormous" and have "a disastrous impact on many small businesses struggling to survive.""Should the Senate Approve the Americans with Disabilities Act of 1989?" Congressional Digest December (1989): 208. The National Federation of Independent Business, an organization that lobbies for small businesses, called the ADA "a disaster for small business".Mandel, Susan. "Disabling the GOP", The National Review November 6, 1990, Vol. 42 Issue 11, pp. 23–24 Pro-business conservative commentators joined in opposition, writing that the Americans with Disabilities Act was "an expensive headache to millions" that would not necessarily improve the lives of people with disabilities.Doherty, Brian. Reason, Aug–Sep 95, Vol. 27 Issue 4, p. 18 |
Americans with Disabilities Act of 1990 | "Capitol Crawl" | "Capitol Crawl"
Shortly before the act was passed, disability rights activists with physical disabilities coalesced in front of the Capitol Building, shed their crutches, wheelchairs, powerchairs and other assistive devices, and immediately proceeded to crawl and pull their bodies up all 100 of the Capitol's front steps, without warning. As the activists did so, many of them chanted "ADA now", and "Vote, Now". Some activists who remained at the bottom of the steps held signs and yelled words of encouragement at the "Capitol Crawlers". Jennifer Keelan, a second grader with cerebral palsy, was videotaped as she pulled herself up the steps, using mostly her hands and arms, saying "I'll take all night if I have to." This direct action is reported to have "inconvenienced" several senators and to have pushed them to approve the act. While there are those who do not attribute much overall importance to this action, the "Capitol Crawl" of 1990 is seen by some present-day disability activists in the United States as a central act for encouraging the ADA into law. |
Americans with Disabilities Act of 1990 | Final passage | Final passage
thumb|right|250px|President Bush signs the Americans with Disabilities Act into law.thumbthumb|House vote and Senate vote
Senator Tom Harkin (D-IA) authored what became the final bill and was its chief sponsor in the Senate. Harkin delivered part of his introduction speech in sign language, saying it was so his deaf brother could understand.
President George H. W. Bush, on signing the measure on July 26, 1990, said: |
Americans with Disabilities Act of 1990 | ADA Amendments Act, 2008 | ADA Amendments Act, 2008
The ADA defines a covered disability as a physical or mental impairment that substantially limits one or more major life activities, a history of having such an impairment, or being regarded as having such an impairment. The Equal Employment Opportunity Commission (EEOC) was charged with interpreting the 1990 law with regard to discrimination in employment. The EEOC developed regulations limiting an individual's impairment to one that "severely or significantly restricts" a major life activity. The ADAAA directed the EEOC to amend its regulations and replace "severely or significantly" with "substantially limits", a more lenient standard.
On September 25, 2008, President George W. Bush signed the ADA Amendments Act of 2008 (ADAAA) into law. The amendment broadened the definition of "disability", thereby extending the ADA's protections to a greater number of people. The ADAAA also added to the ADA examples of "major life activities" including, but not limited to, "caring for oneself, performing manual tasks, seeing, hearing, eating, sleeping, walking, standing, lifting, bending, speaking, breathing, learning, reading, concentrating, thinking, communicating, and working" as well as the operation of several specified "major bodily functions". The act overturned a 1999 US Supreme Court case that held that an employee was not disabled if the impairment could be corrected by mitigating measures; it specifically provides that such impairment must be determined without considering such ameliorative measures. It also overturned the court's finding that an impairment that substantially limits one major life activity must also limit others to be considered a disability.
In 2008, the United States House Committee on Education and Labor stated that the amendment "makes it absolutely clear that the ADA is intended to provide broad coverage to protect anyone who faces discrimination on the basis of disability." Thus the ADAAA led to broader coverage of impaired employees. |
Americans with Disabilities Act of 1990 | Web Content Accessibility Guidelines, 2019 | Web Content Accessibility Guidelines, 2019
In October 2019, the Supreme Court declined to resolve a circuit split as to whether websites are covered by the ADA. The Court turned down an appeal from Domino's Pizza and let stand a U.S. 9th Circuit Court of Appeals ruling which held that the Americans with Disabilities Act protects access not just to brick-and-mortar public accommodations, but also to the websites and apps of those businesses. |
Americans with Disabilities Act of 1990 | Impact | Impact
The ADA led to significant improvements in terms of access to public services, accessibility in the built environment, and societal understanding of disability. |
Americans with Disabilities Act of 1990 | Accessibility | Accessibility |
Americans with Disabilities Act of 1990 | Employment | Employment
Between 1991 (after the enactment of the ADA) and 1995, the employment rate of men with disabilities dropped by 7.8% regardless of age, educational level, or type of disability, with the most affected being young, less-educated and intellectually disabled men. While no causal link between the ADA and that trend has been definitively identified, some researchers have characterized the ADA as ineffectual and argued that it caused this decline by raising the cost of doing business for employers, who quietly avoid hiring people with disabilities for fear of lawsuit. To these employers, hiring people with disabilities became too expensive as they had to spend extra on assistive technology.
In 2001, for men of all working ages and women under 40, Current Population Survey data showed a sharp drop in the employment of disabled workers, leading at least two economists to attribute the cause to the Act. By contrast, a study in 2003 found that while the Act may have led to short term reactions by employers, in the long term, there were either positive or neutral consequences for wages and employment.Douglas Kruse and Lisa Schur, 'Employment of People with Disabilities Following the ADA' (2003) 42(1) Industrial Relations 31 In 2005, the rate of employment among disabled people increased to 45% of the population of disabled people. |
Americans with Disabilities Act of 1990 | Societal attitudes | Societal attitudes |
Americans with Disabilities Act of 1990 | "Professional plaintiffs" | "Professional plaintiffs"
Since enforcement of the act began in July 1992, it has quickly become a major component of employment law. The ADA allows private plaintiffs to receive only injunctive relief (a court order requiring the public accommodation to remedy violations of the accessibility regulations) and attorneys' fees, and does not provide monetary rewards to private plaintiffs who sue non-compliant businesses. Unless a state law, such as the California Unruh Civil Rights Act, provides for monetary damages to private plaintiffs, persons with disabilities do not obtain direct financial benefits from suing businesses that violate the ADA.
The attorneys' fees provision of Title III does provide incentive for lawyers to specialize and engage in serial ADA litigation, but a disabled plaintiff does not obtain a financial reward from attorneys' fees unless they act as their own attorney, or as mentioned above, a disabled plaintiff resides in a state that provides for minimum compensation and court fees in lawsuits. Moreover, there may be a benefit to these private attorneys general who identify and compel the correction of illegal conditions: they may increase the number of public accommodations accessible to persons with disabilities. "Civil rights law depends heavily on private enforcement. Moreover, the inclusion of penalties and damages is the driving force that facilitates voluntary compliance with the ADA."Parr v. L & L Drive-Inn Restaurant (D. Hawaii 2000) 96 F.Supp.2d 1065, 1082, citing and quoting, Committee Print, Vol. II, 101st Cong., 2d Sess., at 1481–82 (1990); (b)(2); S.Rep. No. 101-116, at 15 (1989). Courts have noted:
thumb|California Governor Gavin Newsom speaking about the ADA on the 30th anniversary in 2020
However, in states that have enacted laws that allow private individuals to win monetary awards from non-compliant businesses (as of 2008, these include California, Florida, Hawaii, and Illinois), "professional plaintiffs" are typically found. At least one of these plaintiffs in California has been barred by courts from filing lawsuits unless he receives prior court permission. Through the end of fiscal year 1998, 86% of the 106,988 ADA charges filed with and resolved by the Equal Employment Opportunity Commission, were either dropped or investigated and dismissed by EEOC but not without imposing opportunity costs and legal fees on employers. |
Americans with Disabilities Act of 1990 | Case law | Case law
There have been some notable cases regarding the ADA. For example, a major hotel room marketer (Hotels.com) with their business presence on the Internet was sued because their customers with disabilities could not reserve hotel rooms through their website without substantial extra efforts that persons without disabilities were not required to perform.Smith v. Hotels.com at Disability Rights Advocates Such lawsuits represent a major potential expansion of the ADA in that they (known as "bricks vs. clicks"), seek to expand the ADA's authority to cyberspace, where entities may not have actual physical facilities that are required to comply. |
Americans with Disabilities Act of 1990 | ''Green v. State of California'' | Green v. State of California
Green v. State of California, No. S137770 (Cal. August 23, 2007) was a case in which the California Supreme Court was faced with deciding whether an employee suing the state is required to prove they are able to perform "essential" job duties, regardless of whether or not there was "reasonable accommodation", or if the employer must prove the person suing was unable to do so. The court ruled the burden was on the employee, not the employer, and reversed a disputed decision by the lower courts. Plaintiff attorney David Greenberg brought forth considerations of the concept that, even in the state of California, employers do not have to employ a worker who is unable to perform "essential job functions" with "reasonable accommodation". Forcing employers to do so "would defy logic and establish a poor public policy in employment matters." |
Americans with Disabilities Act of 1990 | ''National Federation of the Blind v. Target Corporation'' | National Federation of the Blind v. Target Corporation
National Federation of the Blind v. Target Corp. was a case where a major retailer, Target Corp., was sued because their web designers failed to design its website to enable persons with low or no vision to use it.National Federation for the Blind v. Target at Disability Rights Advocates |
Americans with Disabilities Act of 1990 | ''Board of Trustees of the University of Alabama v. Garrett'' | Board of Trustees of the University of Alabama v. Garrett
Board of Trustees of the University of Alabama v. Garrett was a United States Supreme Court case about Congress's enforcement powers under the Fourteenth Amendment to the Constitution. It decided that Title I of the Americans with Disabilities Act was unconstitutional insofar as it allowed private citizens to sue states for money damages. |
Americans with Disabilities Act of 1990 | ''Barden v. The City of Sacramento'' | Barden v. The City of Sacramento
Barden v. The City of Sacramento, filed in March 1999, claimed that the City of Sacramento failed to comply with the ADA when, while making public street improvements, it did not bring its sidewalks into compliance with the ADA. Certain issues were resolved in federal court. One issue, whether sidewalks were covered by the ADA, was appealed to the 9th Circuit Court of Appeals, which ruled that sidewalks were a "program" under the ADA and must be made accessible to persons with disabilities. The ruling was later appealed to the U.S. Supreme Court, which refused to hear the case, letting stand the ruling of the 9th Circuit. |
Americans with Disabilities Act of 1990 | ''Bates v. United Parcel Service, Inc'' | Bates v. United Parcel Service, Inc
Bates v. United Parcel Service, Inc (UPS; begun in 1999) was the first equal opportunity employment class action brought on behalf of Deaf and Hard of Hearing workers throughout the country concerning workplace discrimination. It established legal precedent for these employees to be fully covered under the ADA. Key findings included:
UPS failed to address communication barriers and to ensure equal conditions and opportunities for deaf employees;
Deaf employees were routinely excluded from workplace information, denied opportunities for promotion, and exposed to unsafe conditions due to lack of accommodations by UPS;
UPS also lacked a system to alert these employees as to emergencies, such as fires or chemical spills, to ensure that they would safely evacuate their facility; and
UPS had no policy to ensure that deaf applicants and employees actually received effective communication in the workplace.
The outcome was that UPS agreed to pay a $5.8 million award and agreed to a comprehensive accommodations program that was implemented in their facilities throughout the country. |
Americans with Disabilities Act of 1990 | ''Spector v. Norwegian Cruise Line Ltd.'' | Spector v. Norwegian Cruise Line Ltd.
Spector v. Norwegian Cruise Line Ltd.. was a case that was decided by the United States Supreme Court in 2005. The defendant argued that as a vessel flying the flag of a foreign nation it was exempt from the requirements of the ADA. This argument was accepted by a federal court in Florida and, subsequently, the Fifth Circuit Court of Appeals. However, the U.S. Supreme Court reversed the ruling of the lower courts on the basis that Norwegian Cruise Lines was a business headquartered in the United States whose clients were predominantly Americans and, more importantly, operated out of port facilities throughout the United States. |
Americans with Disabilities Act of 1990 | ''Olmstead v. L.C.'' | Olmstead v. L.C.
Olmstead v. L.C.. was a case before the United States Supreme Court in 1999. The two plaintiffs, Lois Curtis and E.W., were institutionalized in Georgia for diagnosed "mental retardation" and schizophrenia. Clinical assessments by the state determined that the plaintiffs could be appropriately treated in a community setting rather than the state institution. The plaintiffs sued the state of Georgia and the institution for being inappropriately treated and housed in the institutional setting rather than being treated in one of the state's community-based treatment facilities.
The Supreme Court decided under Title II of the ADA that mental illness is a form of disability and therefore covered under the ADA, and that unjustified institutional isolation of a person with a disability is a form of discrimination because it "...perpetuates unwarranted assumptions that persons so isolated are incapable or unworthy of participating in community life." The court added, "Confinement in an institution severely diminishes the everyday life activities of individuals, including family relations, social contacts, work options, economic independence, educational advancement, and cultural enrichment."
Therefore, under Title II no person with a disability can be unjustly excluded from participation in or be denied the benefits of services, programs or activities of any public entity. |
Americans with Disabilities Act of 1990 | ''Michigan Paralyzed Veterans of America v. The University of Michigan'' | Michigan Paralyzed Veterans of America v. The University of Michigan
Michigan Paralyzed Veterans of America v. The University of Michigan was a case filed before the United States District Court for the Eastern District of Michigan. It was filed on behalf of the Michigan Paralyzed Veterans of America against the University of Michigan claiming that Michigan Stadium violated the Americans with Disabilities Act in its $226-million renovation by failing to add enough seats for disabled fans or accommodate the needs for disabled restrooms, concessions and parking. Additionally, the distribution of the accessible seating was at issue, with nearly all the seats being provided in the end-zone areas. The U.S. Department of Justice assisted in the suit, which was settled in March 2008.Erb, Robin. "U-M fans rave about new seats for disabled", Detroit Free Press. September 9, 2008. The settlement required the stadium to add 329 wheelchair seats throughout the stadium by 2010, and an additional 135 accessible seats in clubhouses to go along with the existing 88 wheelchair seats. This case was significant because it set a precedent for the uniform distribution of accessible seating and gave the DOJ the opportunity to clarify previously unclear rules.Wolffe, Jerry. "New wheelchair seats will be full at U-M's Big House." The Oakland Press. September 14, 2008. The agreement now is a blueprint for all stadiums and other public facilities regarding accessibility. |
Americans with Disabilities Act of 1990 | ''Paralyzed Veterans of America v. Ellerbe Becket Architects and Engineers'' | Paralyzed Veterans of America v. Ellerbe Becket Architects and Engineers
One of the first major ADA lawsuits, Paralyzed Veterans of America v. Ellerbe Becket Architects and Engineers (PVA 1996) was focused on the wheelchair accessibility of a stadium project that was still in the design phase, MCI Center (now known as Capital One Arena) in Washington, D.C. Previous to this case, which was filed only five years after the ADA was passed, the DOJ was unable or unwilling to provide clarification on the distribution requirements for accessible wheelchair locations in large assembly spaces. While Section 4.33.3 of ADAAG makes reference to lines of sight, no specific reference is made to seeing over standing patrons. The MCI Center, designed by Ellerbe Becket Architects & Engineers, was designed with too few wheelchair and companion seats, and the ones that were included did not provide sight lines that would enable the wheelchair user to view the playing area while the spectators in front of them were standing. This case and another related case established precedent on seat distribution and sight lines issues for ADA enforcement that continues to present day. |
Americans with Disabilities Act of 1990 | ''Toyota Motor Manufacturing, Kentucky, Inc. v. Williams'' | Toyota Motor Manufacturing, Kentucky, Inc. v. Williams
Toyota Motor Manufacturing, Kentucky, Inc. v. Williams,. was a case in which the US Supreme Court interpreted the meaning of the phrase "substantially impairs" as used in the Americans with Disabilities Act. It reversed a Sixth Circuit Court of Appeals decision to grant partial summary judgment in favor of the respondent, Ella Williams, that classified her inability to perform manual job-related tasks as a disability. The Court held that the "major life activity" definition for evaluating the performance of manual tasks focuses the inquiry on whether Williams was unable to perform a range of tasks central to most people in carrying out the activities of daily living, not whether Williams was unable to perform her specific job tasks. Therefore, the determination of whether an impairment rises to the level of a disability is not limited to activities in the workplace solely, but rather to manual tasks in life in general. When the Supreme Court applied this standard, it found that the Court of Appeals had incorrectly determined the presence of a disability because it relied solely on her inability to perform specific manual work tasks, which was insufficient in proving the presence of a disability. The Court of Appeals should have taken into account the evidence presented that Williams retained the ability to do personal tasks and household chores, such activities being the nature of tasks most people do in their daily lives, and placed too much emphasis on her job disability. Since the evidence showed that Williams was performing normal daily tasks, it ruled that the Court of Appeals erred when it found that Williams was disabled. This ruling has since been legislatively overturned by the ADA Amendments Act of 2008 (ADAAA). In fact, Congress explicitly cited Toyota v. Williams in the text of the ADAAA itself as one of its driving influences for passing the ADAAA. |
Americans with Disabilities Act of 1990 | ''US Airways, Inc. v. Barnett'' | US Airways, Inc. v. Barnett
US Airways, Inc. v. Barnett was decided by the US Supreme Court in 2002. This case. held that even requests for accommodation that might seem reasonable on their face, e.g., a transfer to a different position, can be rendered unreasonable because it would require a violation of the company's seniority system. While the court held that, in general, a violation of a seniority system renders an otherwise reasonable accommodation unreasonable, a plaintiff can present evidence that, despite the seniority system, the accommodation is reasonable in the specific case at hand, e.g., the plaintiff could offer evidence that the seniority system is so often disregarded that another exception would not make a difference.
Importantly, the court held that the defendant need not provide proof that this particular application of the seniority system should prevail, and that, once the defendant showed that the accommodation violated the seniority system, it fell to Barnett to show it was nevertheless reasonable.
In this case, Barnett was a US Airways employee who injured his back, rendering him physically unable to perform his cargo-handling job. Invoking seniority, he transferred to a less-demanding mailroom job, but this position later became open to seniority-based bidding and was bid on by more senior employees. Barnett requested the accommodation of being allowed to stay on in the less-demanding mailroom job. US Airways denied his request, and he lost his job.
The Supreme Court decision invalidated both the approach of the district court, which found that the mere presence and importance of the seniority system was enough to warrant a summary judgment in favor of US Airways, as well as the circuit court's approach that interpreted 'reasonable accommodation' as 'effective accommodation.' |
Americans with Disabilities Act of 1990 | ''Access Now v. Southwest Airlines'' | Access Now v. Southwest Airlines
Access Now, Inc. v. Southwest Airlines Co. was a 2002 case where the District Court decided that the website of Southwest Airlines was not in violation of the Americans with Disabilities Act, because the ADA is concerned with things with a physical existence and thus cannot be applied to cyberspace. Judge Patricia A. Seitz found that the "virtual ticket counter" of the website was a virtual construct, and hence not a "public place of accommodation". As such, "To expand the ADA to cover 'virtual' spaces would be to create new rights without well-defined standards." |
Americans with Disabilities Act of 1990 | ''Ouellette v. Viacom International Inc.'' | Ouellette v. Viacom International Inc.
Ouellette v. Viacom International Inc. (2011) held that a mere online presence does not subject a website to the ADA guidelines. Thus Myspace and YouTube were not liable for a dyslexic man's inability to navigate the site regardless of how impressive the "online theater" is. |
Americans with Disabilities Act of 1990 | ''Authors Guild v. HathiTrust'' | Authors Guild v. HathiTrust
Authors Guild v. HathiTrust was a case in which the District Court decided that the HathiTrust digital library was a transformative, fair use of copyrighted works, making a large number of written text available to those with print disability. |
Americans with Disabilities Act of 1990 | ''Zamora-Quezada v. HealthTexas Medical Group'' | Zamora-Quezada v. HealthTexas Medical Group
Zamora-Quezada v. HealthTexas Medical Group (begun in 1998) was the first time this act was used against HMOs when a novel lawsuit was filed by Texas attorney Robert Provan against five HMOs for their practice of revoking the contracts of doctors treating disabled patients. In 1999, these HMOs sought to dismiss Provan's lawsuit, but a federal court ruled against them, and the case was settled out of court. Many decisions relating to Provan's unique lawsuit against these HMOs have been cited in other court cases since. |
Americans with Disabilities Act of 1990 | ''Campbell v. General Dynamics Government Systems Corp.'' | Campbell v. General Dynamics Government Systems Corp.
Campbell v. General Dynamics Government Systems Corp. (2005) concerned the enforceability of a mandatory arbitration agreement contained in a dispute resolution policy linked to an e-mailed company-wide announcement, insofar as it applies to employment discrimination claims brought under the Americans with Disabilities Act. |
Americans with Disabilities Act of 1990 | ''Tennessee v. Lane'' | Tennessee v. Lane
Tennessee v. Lane,. 541 U.S. 509 (2004), was a case in the Supreme Court of the United States involving Congress's enforcement powers under section 5 of the Fourteenth Amendment. George Lane was unable to walk after a 1997 car accident in which he was accused of driving on the wrong side of the road. A woman was killed in the crash, and Lane faced misdemeanor charges of reckless driving. The suit was brought about because he was denied access to appear in criminal court because the courthouse had no elevator, even though the court was willing to carry him up the stairs and then willing to move the hearing to the first floor. He refused, citing he wanted to be treated as any other citizen, and was subsequently charged with failure to appear, after appearing at a previous hearing where he dragged himself up the stairs. The court ruled that Congress did have enough evidence that disabled people were being denied those fundamental rights that are protected by the Due Process clause of the Fourteenth Amendment and had the enforcement powers under section 5 of the Fourteenth Amendment. It further ruled that "reasonable accommodations" mandated by the ADA were not unduly burdensome and disproportionate to the harm. |
Americans with Disabilities Act of 1990 | Gender dysphoria | Gender dysphoria
In 2022, the United States Court of Appeals for the Fourth Circuit stated that the ADA covers individuals with gender dysphoria, which may aid transgender people in accessing legal protections they otherwise may be unable to. |
Americans with Disabilities Act of 1990 | See also | See also |
Americans with Disabilities Act of 1990 | References | References |
Americans with Disabilities Act of 1990 | Further reading | Further reading
Bush, George H. W., Remarks of President George Bush at the Signing of the Americans with Disabilities Act. Available online at Equal Employment Opportunity Commission.
Davis, Lennard J. Enabling Acts. The Hidden Story of How the Americans with Disabilities Act Gave the Largest US Minority Its Rights. Boston, MA: Beacon Press, 2015.
Fielder, J. F. Mental Disabilities and the Americans with Disabilities Act. Westport, CT: Quorum Books, 2004.
Hamilton Krieger, Linda, ed., Backlash Against the ADA: Reinterpreting Disability Rights Ann Arbor: University of Michigan Press, 2003.
Johnson, Mary. (2000). Make Them Go Away: Clint Eastwood, Christopher Reeve & the Case Against Disability Rights. Louisville, KY: The Advocado Press.
Mayer, Arlene. (1992). The History of the Americans with Disabilities Act: A Movement Perspective. Available online at the Disability Rights Education & Defense Fund website
O'Brien, Ruth, ed. Voices from the Edge: Narratives about the Americans with Disabilities Act. New York: Oxford, 2004.
Pletcher, David and Ashlee Russeau-Pletcher. History of the Civil Rights Movement for the Physically Disabled
Switzer, Jacqueline Vaughn. Disabled Rights: American Disability Policy and the Fight for Equality. Washington, D.C.: Georgetown University Press, 2003.
Weber, Mark C. Disability Harassment. New York: NYU Press, 2007. |
Americans with Disabilities Act of 1990 | External links | External links
from the DOJ Civil Rights Division
ADA page from the Department of Labor
ADA page from the Equal Employment Opportunity Commission
As codified in 42 U.S.C. chapter 126 of the United States Code from the US House of Representatives
As codified in 42 U.S.C. chapter 126 of the United States Code from the LII
Americans with Disabilities Act of 1990 as amended (PDF/details) in the GPO Statute Compilations collection
Family Network on Disabilities FNDUSA.ORG—Florida Parent Training and Information Center funded by DOED Offices of Special Education Programs (OSEP)
Lainey Feingold's Global Law and Policy: United States – federal (national)
What is ADA compliance? How to Create an ADA-Compliant PDF?
Category:101st United States Congress
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Category:Civil rights in the United States
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Category:United States federal disability legislation
Category:Civil Rights Acts |
Americans with Disabilities Act of 1990 | Table of Content | short description, Disabilities included, Titles, Title I—employment <span class="anchor" id="Title I"></span>, Title II—public entities (and public transportation) <span class="anchor" id="Title II"></span>, Title III—public accommodations (and commercial facilities) <span class="anchor" id="Title III"></span>, Service animals, Auxiliary aids <span class="anchor" id="Auxiliary aid"></span>, Title IV—telecommunications <span class="anchor" id="Title IV"></span>, Title V—miscellaneous provisions <span class="anchor" id="Title V"></span>, History, Drafting, Lobbying, Support and opposition, Support, Opposition from religious groups, Opposition from business interests, "Capitol Crawl", Final passage, ADA Amendments Act, 2008, Web Content Accessibility Guidelines, 2019, Impact, Accessibility, Employment, Societal attitudes, "Professional plaintiffs", Case law, ''Green v. State of California'', ''National Federation of the Blind v. Target Corporation'', ''Board of Trustees of the University of Alabama v. Garrett'', ''Barden v. The City of Sacramento'', ''Bates v. United Parcel Service, Inc'', ''Spector v. Norwegian Cruise Line Ltd.'', ''Olmstead v. L.C.'', ''Michigan Paralyzed Veterans of America v. The University of Michigan'', ''Paralyzed Veterans of America v. Ellerbe Becket Architects and Engineers'', ''Toyota Motor Manufacturing, Kentucky, Inc. v. Williams'', ''US Airways, Inc. v. Barnett'', ''Access Now v. Southwest Airlines'', ''Ouellette v. Viacom International Inc.'', ''Authors Guild v. HathiTrust'', ''Zamora-Quezada v. HealthTexas Medical Group'', ''Campbell v. General Dynamics Government Systems Corp.'', ''Tennessee v. Lane'', Gender dysphoria, See also, References, Further reading, External links |
Apple I | Short description | The Apple Computer 1 (Apple-1), later known predominantly as the Apple I, is an 8-bit personal computer designed by Steve Wozniak and released by the Apple Computer Company (now Apple Inc.) in 1976. The company was initially formed to sell the Apple Iits first product and would later become the world's largest technology company. The idea of starting a company and selling the computer came from Wozniak's friend and Apple co-founder Steve Jobs. A differentiator of the Apple I was that it included video display terminal circuitry on its circuit board, allowing it to connect to a low-cost composite video monitor or television, whereas others avoided this and used more expensive monitors because business was used to more characters per displayed/typewritten line. The Apple I and the Sol-20 were some of the first home computers to have this capability.
To finance the Apple I's development, Wozniak and Jobs sold some of their possessions for a few hundred dollars. Wozniak demonstrated the first prototype in July 1976 at the Homebrew Computer Club in Palo Alto, California, impressing the Byte Shop, an early computer retailer. After securing an order for 50 computers, Jobs was able to order the parts on credit and deliver the first Apple products after ten days.
The Apple I was one of the first computers available that used the MOS Technology 6502 microprocessor. An expansion included a BASIC interpreter, allowing users to utilize BASIC at home instead of at institutions with mainframe computers, greatly lowering the entry cost for computing with BASIC.
Production was discontinued on September 30, 1977, after the June 10, 1977 introduction of its successor, the Apple II, which Byte magazine referred to as part of the "1977 Trinity" of personal computing (along with the PET 2001 from Commodore Business Machines and the TRS-80 Model I from Tandy Corporation). As relatively few computers were made before they were discontinued, coupled with their status as Apple's first product, surviving Apple I units are now displayed in computer museums. |
Apple I | History | History |
Apple I | Development | Development
thumb|Steve Wozniak alone designed the circuit and operating system for the Apple I.
In 1974, while visiting famous phone phreak John Draper in California, Steve Wozniak watched him connect a modem to the ARPANET – the precursor to the internet – and use a teleprinter to play chess with someone from Boston; this inspired him to make a cheap terminal that used an inexpensive keyboard from Sears and a standard TV. Later in March 1975, Wozniak started attending meetings of the Homebrew Computer Club, which was a major source of inspiration for him. New microcomputers such as the Altair 8800 inspired Wozniak to build a microprocessor into his video terminal circuit to make a complete computer. At the time the only appropriate CPUs available were the Intel 8080, and the Motorola 6800. Of these options, Wozniak preferred the 6800, though he was financially unable to obtain either. Instead, he began designing computers on paper until he could afford a CPU.
When the $25 MOS Technology 6502 was released in late 1975, Wozniak wrote a version of BASIC for it, then began to design a computer for it to run on. The 6502 was developed by many of the same engineers that designed the 6800, as many in Silicon Valley left employers to form their own companies. Wozniak's earlier 6800 computer design needed only minor changes to run on the new processor.
By March 1, 1976, Wozniak completed the basic design of his computer. Wozniak originally offered the design to HP while working there, but it was rejected by the company on five occasions. When he demonstrated his computer at the Homebrew Computer Club, his friend and fellow club regular Steve Jobs was immediately interested in its commercial potential. Wozniak intended to share schematics of the machine for free; however, Jobs advised him to start a business together and sell bare printed circuit boards for the computer, without any components soldered on. Wozniak, at first skeptical, was later convinced by Jobs that even if they were not successful they could at least say to their grandchildren that they had had their own company. To raise the money they needed to build the first batch of the circuit boards, Wozniak sold his HP-65 scientific calculator while Jobs sold his Volkswagen van.
After the company was formed a month later, Jobs and Wozniak gave a presentation of the fully assembled "Apple Computer A" at the Homebrew Computer Club. Paul Terrell, who was starting a new computer shop in Mountain View, California, called the Byte Shop, saw the presentation and was impressed by the machine. Terrell told Jobs that he would order 50 units of the Apple I and pay $500 each on delivery, but only if they came fully assembledhe was not interested in buying bare printed circuit boards with no components.
Jobs took the purchase order from the Byte Shop to national electronic parts distributor Cramer Electronics, and ordered the components needed. When asked by the credit manager how he would pay for the parts, Jobs replied, "I have this purchase order from the Byte Shop chain of computer stores for 50 of my computers and the payment terms are COD. If you give me the parts on net 30-day terms I can build and deliver the computers in that time frame, collect my money from Terrell at the Byte Shop and pay you."
To verify the purchase order, the credit manager called Paul Terrell, who assured him if the computers showed up, Jobs would have more than enough money for the parts order. The two Steves and their small crew spent day and night building and testing the computers, and delivered to Terrell on time. Terrell was surprised to receive a batch of assembled circuit boards, as he had expected complete computers with a case, monitor and keyboard. Nonetheless, he kept his word and paid the two Steves the money promised. |
Apple I | Announcement and sales | Announcement and sales
thumb|Introductory advertisement for the Apple I computer
The Apple I went on sale in July 1976 at a price of . Wozniak later said he had no idea about the relation between the number and the number of the beast, and that he came up with the price because he liked "repeating digits" and because it was a one-third markup on the wholesale price. Jobs had managed to get the inventory into the nation's first four storefront microcomputer retailers: Byte Shop (Palo Alto, California), itty bitty machine company (Evanston, Illinois), Data Domain (Bloomington, Indiana), and Computer Mart (New York City).
The first unit produced was used in a high school math class, and donated to Liza Loop's public-access computer center. About 200 units were produced, and all but 25 were sold within nine or ten months.
In April 1977, the price was dropped to $475. It continued to be sold through August 1977, despite the introduction of the Apple II in April 1977, which began shipping in June of that year. In October 1977, the Apple I was officially discontinued and removed from Apple's price list. As Wozniak was the only person who could answer most customer support questions about the computer, the company offered Apple I owners discounts and trade-ins for Apple IIs to persuade them to return their computers. These recovered boards were then destroyed by Apple, contributing to their later rarity.
Both Steve Jobs and Steve Wozniak have stated that Apple did not assign serial numbers to the Apple l. Several boards have been found with numbered stickers affixed to them, which appear to be inspection stickers from the PCB manufacturer/assembler. A batch of boards is known to have numbers hand-written in black permanent marker on the back; these usually appear as "01-00##". As of January 2022, 29 Apple-1s with a serial number are known. The highest known number is . Two original Apple-1s have been analyzed by Professional Sports Authenticator in Los Angeles, concluding that the serial numbers had been hand-written by Steve Jobs. |
Apple I | Hardware | Hardware
The Apple I used a MOS Technology 6502 microprocessor running at , and its design was based largely on Wozniak's previous work centered around a Motorola 6800. The unconventional clock speed was chosen to be a fraction () of the NTSC color carrier, which simplified video circuitry. of memory was included on the base machine, which was expandable to on-board and up to by using an add-on card. On-board memory utilized newly available 4Kbit DRAM chips, and was designed to be upgradeable to the next generation of 16Kbit chips for a maximum of on-board memory.Apple I advertisement Oct 1978 An optional $75 plug-in cassette interface card allowed users to store programs on ordinary audio cassette tapes. A BASIC interpreter, originally written by Wozniak, was provided with the cassette interface that let users easily write programs and play simple games. An onboard AC power supply was included.
The Apple I did not come with a case. It could be used bare, although some users chose to build custom (typically wooden) enclosures. |
Apple I | Memory map | Memory map
+AddressSize Description0x0000 - 0x002336 BytesRAM4K systems
(minimal system, cannot load wozbasic))0x0024 - 0x002B8 Byteswozmon variables0x002C - 0x00FF212 BytesRAM0x0100 - 0x01FF256 Bytes6502 processor stack0x0200 - 0x027F128 Byteswozmon keyboard input buffer0x0280 - 0x0FFF3456 BytesRAM0x1000 - 0xC027UnusedUser expandable RAM / IO0xC0281 ByteACI port to write to cassette0xC029 - 0xC0FFUnusedUser expandable RAM / IO0xC100 - 0xC1FF256 BytesACI ROMWhen ACI card is inserted0xC200 - 0xD00FUnusedUser expandable RAM / IO0xD010 - 0xD0134 BytesPIA (Peripheral Interface Adapter)Keyboard and Display0xD014 - 0xDFFFUnusedUser expandable RAM / IO0xE000 - 0xEFFF4Ki (4096 Bytes)RAM8K systems
(standard system, can load wozbasic)0xF000 - 0xFEFFUnusedUser expandable RAM / IO0xFF00 - 0xFFFF256 BytesPROM (wozmon)Programmable read-only memory
alt=A backlash character at the top-left of the screen and a blinking ampersand character below it|thumb|208x208px|The Apple-1 system monitor ready prompt |
Apple I | Video and Input | Video and Input
The Apple I included built-in computer terminal circuitry with composite video output. To use the computer, a user-supplied composite monitor and ASCII-encoded keyboard needed to be connected. If a monitor was not available, a standard television set could be used along with an RF modulator. In comparison, competing machines generally required an expensive dedicated video display terminal or teletypewriter. This, combined with its single-board construction, made the Apple I an elegant and inexpensive machine for its day, though competitors such as the Sol-20 and Sphere 1 offered similar feature sets.
The computer generated its video output using a shift register memory and a Signetics 2513 64×8×5 Character Generator. It was capable of displaying uppercase characters, numbers and basic punctuation and math symbols with a 5x8 pixel font: |
Apple I | Apple Cassette Interface expansion | Apple Cassette Interface expansion
A cassette interface was available in the form of an optional add-on for the Apple I's expansion slot. A cassette deck plugged in to the expansion's phone connector ports could be written to and read from as a form of removable storage. The only alternative to the interface for loading programs was typing machine code by hand, making the add-on "ubiquitous".
The expansion came with a free cassette tape containing Steve Wozniak's Integer BASIC interpreter. Other software tapes were supplied "at minimal cost" including ported video games such as Hamurabi, Lunar Lander and Star Trek. |
Apple I | Conservation | Conservation
thumb|A running Apple I, with a keyboard and monitor connected, on display at LCM+L where guests were allowed to use it
Only about 200 Apple I boards were produced, and the whereabouts of 62 to 82 are known. After the success of the Apple II, and of Apple broadly, the Apple I was recognized as an important historical computer. According to the 1986 Apple IIe Owner's Guide, an Apple I was then worth "between $10,000 and $15,000" and a board was reportedly sold for $50,000 in 1999.
In November 2010, an Apple I with a cache of original documents and packaging sold for £133,250 ($) at Christie's auction house in London. The documents included the return label showing Steve Jobs's parents' address, a personally typed and signed letter from Jobs (answering technical questions about the computer), and the invoice (listing "Steven" as the salesman). The computer was brought to Polytechnic University of Turin for restoration.
In October 2014 the Henry Ford Museum purchased an Apple I at a Bonhams auction for . The sale included the keyboard, monitor, cassette decks and a manual. In 2017, an Apple I removed from Steve Jobs's office in 1985 by Apple quality control engineer Don Hutmacher was placed on display at Living Computers: Museum + Labs.
On May 30, 2015, an elderly woman reportedly dropped off boxes of electronics for disposal at an electronics recycling center in the Silicon Valley of Northern California. Included in the electronics (removed from her garage after the death of her husband) was an original Apple I computer, which the recycling firm sold for . When a discarded item is sold, it is the company's practice to give 50% of the proceeds to the original owner, but the woman has not been identified.
Apple I computers with original documents and memorabilia have frequently been auctioned for over $300,000 throughout the 2010s and 2020s. The production prototype for the Apple I survives in a badly damaged state and was itself auctioned in 2022 for $677,196. |
Apple I | Replicas | Replicas
Several Apple I clones and replicas have been released in recent years. These are created by hobbyists and marketed to the hobbyist/collector community. Availability is usually limited to small runs in response to demand.replica I – the apple I(c) clone , retrieved August 15, 2009replica I at official Briel computers web site, retrieved August 15, 2008 story with pictures for assembling a Briel replica I from a kit Retrieved December 1, 2022 |
Apple I | Emulation | Emulation
Emulation software for the Apple I has been written for modern home computersPom1 Apple 1 Emulator , retrieved July 17, 2013CocoaPom Apple 1 Emulator , retrieved July 17, 2013Sim6502 Apple I emulator retrieved July 17, 2013 and for web browsers. It has also been emulated on 1980s era computers including the SAM CoupéApple 1 Emulator - SAM Coupé , retrieved July 17, 2013 and Commodore 64. |
Apple I | See also | See also
Computer museum
History of computer science
History of computing
KIM-1 |
Apple I | Notes | Notes |
Apple I | References | References |
Apple I | Citations | Citations |
Apple I | Sources | Sources
|
Apple I | External links | External links
Apple I Owners Club
Apple I Operational Manual (browse)
German making-of article to recreate the Apple I Operational Manual
Apple I project on www.sbprojects.com
Apple 1 Computer Registry
John Calande III blog – Building the Apple I clone, including corrections on the early history of Apple Computer
Apple 1 | Cameron's Closet – includes display of the Apple 1's character set on real hardware, compared to on most emulators
Category:Computer-related introductions in 1976
Category:Apple II family
I
Category:Early microcomputers
Category:6502-based home computers
Category:Products and services discontinued in 1977
Category:Discontinued Apple Inc. products
Category:Steve Jobs |
Apple I | Table of Content | Short description, History, Development, Announcement and sales, Hardware, Memory map, Video and Input, Apple Cassette Interface expansion, Conservation, Replicas, Emulation, See also, Notes, References, Citations, Sources, External links |
Apatosaurus | short description | Apatosaurus (; meaning "deceptive lizard") is a genus of herbivorous sauropod dinosaur that lived in North America during the Late Jurassic period. Othniel Charles Marsh described and named the first-known species, A. ajax, in 1877, and a second species, A. louisae, was discovered and named by William H. Holland in 1916. Apatosaurus lived about 152 to 151 million years ago (mya), during the late Kimmeridgian to early Tithonian age, and are now known from fossils in the Morrison Formation of modern-day Colorado, Oklahoma, New Mexico, Wyoming, and Utah in the United States. Apatosaurus had an average length of , and an average mass of . A few specimens indicate a maximum length of 11–30% greater than average and a mass of approximately .
The cervical vertebrae of Apatosaurus are less elongated and more heavily constructed than those of Diplodocus, a diplodocid like Apatosaurus, and the bones of the leg are much stockier despite being longer, implying that Apatosaurus was a more robust animal. The tail was held above the ground during normal locomotion. Apatosaurus had a single claw on each forelimb and three on each hindlimb. The Apatosaurus skull, long thought to be similar to Camarasaurus, is much more similar to that of Diplodocus. Apatosaurus was a generalized browser that likely held its head elevated. To lighten its vertebrae, Apatosaurus had air sacs that made the bones internally full of holes. Like that of other diplodocids, its tail may have been used as a whip to create loud noises, or, as more recently suggested, as a sensory organ.
The skull of Apatosaurus was confused with that of Camarasaurus and Brachiosaurus until 1909, when the holotype of A. louisae was found, and a complete skull just a few meters away from the front of the neck. Henry Fairfield Osborn disagreed with this association, and went on to mount a skeleton of Apatosaurus with a Camarasaurus skull cast. Apatosaurus skeletons were mounted with speculative skull casts until 1970, when McIntosh showed that more robust skulls assigned to Diplodocus were more likely from Apatosaurus.
Apatosaurus is a genus in the family Diplodocidae. It is one of the more basal genera, with only Amphicoelias and possibly a new, unnamed genus more primitive. Although the subfamily Apatosaurinae was named in 1929, the group was not used validly until an extensive 2015 study. Only Brontosaurus is also in the subfamily, with the other genera being considered synonyms or reclassified as diplodocines. Brontosaurus has long been considered a junior synonym of Apatosaurus; its type species was reclassified as A.excelsus in 1903. A 2015 study concluded that Brontosaurus is a valid genus of sauropod distinct from Apatosaurus, but not all paleontologists agree with this division. As it existed in North America during the late Jurassic, Apatosaurus would have lived alongside dinosaurs such as Allosaurus, Camarasaurus, Diplodocus, and Stegosaurus. |
Apatosaurus | Description | Description
thumb|left|Comparison of A. ajax (orange) and A.louisae (red) with a human (blue) and Brontosaurus parvus (green)
Apatosaurus was a large, long-necked, quadrupedal animal with a long, whip-like tail. Its forelimbs were slightly shorter than its hindlimbs. Most size estimates are based on specimen CM3018, the type specimen of A.louisae, reaching in length and in body mass. A 2015 study that estimated the mass of volumetric models of Dreadnoughtus, Apatosaurus, and Giraffatitan estimates CM3018 at , similar in mass to Dreadnoughtus. Some specimens of A.ajax (such as OMNH1670) represent individuals 1130% longer, suggesting masses twice that of CM3018 or , potentially rivaling the largest titanosaurs. However, the upper size estimate of OMNH1670 is likely an exaggeration, with the size estimates revised in 2020 at in length and in body mass based on volumetric analysis.
thumb|A. ajax skull, specimen CMC VP 7180
The skull is small in relation to the size of the animal. The jaws are lined with spatulate (chisel-like) teeth suited to an herbivorous diet. The snout of Apatosaurus and similar diplodocoids is squared, with only Nigersaurus having a squarer skull. The braincase of Apatosaurus is well preserved in specimen BYU17096, which also preserved much of the skeleton. A phylogenetic analysis found that the braincase had a morphology similar to those of other diplodocoids. Some skulls of Apatosaurus have been found still in articulation with their teeth. Those teeth that have the enamel surface exposed do not show any scratches on the surface; instead, they display a sugary texture and little wear.
thumb|left|Cervical vertebra of A. ajax (holotype, YPM 1860) in side and anterior view
Like those of other sauropods, the neck vertebrae are deeply bifurcated; they carried neural spines with a large trough in the middle, resulting in a wide, deep neck. The vertebral formula for the holotype of A.louisae is 15cervicals, 10dorsals, 5sacrals, and 82caudals. The caudal vertebra number may vary, even within species. The cervical vertebrae of Apatosaurus and Brontosaurus are stouter and more robust than those of other diplodocids and were found to be most similar to Camarasaurus by Charles Whitney Gilmore. In addition, they support cervical ribs that extend farther towards the ground than in diplodocines, and have vertebrae and ribs that are narrower towards the top of the neck, making the neck nearly triangular in cross-section. In Apatosaurus louisae, the atlas-axis complex of the first cervicals is nearly fused. The dorsal ribs are not fused or tightly attached to their vertebrae and are instead loosely articulated. Apatosaurus has ten dorsal ribs on either side of the body. The large neck was filled with an extensive system of weight-saving air sacs. Apatosaurus, like its close relative Supersaurus, has tall neural spines, which make up more than half the height of the individual bones of its vertebrae. The shape of the tail is unusual for a diplodocid; it is comparatively slender because of the rapidly decreasing height of the vertebral spines with increasing distance from the hips. Apatosaurus also had very long ribs compared to most other diplodocids, giving it an unusually deep chest. As in other diplodocids, the tail transformed into a whip-like structure towards the end.
thumb|Artistic interpretation of A. louisae
The limb bones are also very robust. Within Apatosaurinae, the scapula of Apatosaurus louisae is intermediate in morphology between those of A.ajax and Brontosaurus excelsus. The arm bones are stout, so the humerus of Apatosaurus resembles that of Camarasaurus, as well as Brontosaurus. However, the humeri of Brontosaurus and A.ajax are more similar to each other than they are to A.louisae. In 1936, Charles Gilmore noted that previous reconstructions of Apatosaurus forelimbs erroneously proposed that the radius and ulna could cross; in life they would have remained parallel. Apatosaurus had a single large claw on each forelimb, a feature shared by all sauropods more derived than Shunosaurus. The first three toes had claws on each hindlimb. The phalangeal formula is 2-1-1-1-1, meaning the innermost finger (phalanx) on the forelimb has two bones and the next has one. The single manual claw bone (ungual) is slightly curved and squarely truncated on the anterior end. The pelvic girdle includes the robust ilia, and the fused (co-ossified) pubes and ischia. The femora of Apatosaurus are very stout and represent some of the most robust femora of any member of Sauropoda. The tibia and fibula bones are different from the slender bones of Diplodocus but are nearly indistinguishable from those of Camarasaurus. The fibula is longer and slenderer than the tibia. The foot of Apatosaurus has three claws on the innermost digits; the digit formula is 3-4-5-3-2. The first metatarsal is the stoutest, a feature shared among diplodocids. |
Apatosaurus | Discovery and species | Discovery and species |
Apatosaurus | Initial discovery | Initial discovery
left|thumb|Arthur Lakes' painting of YPM crews excavating fossils of Apatosaurus ajax at Quarry 10 in Morrison.
The first Apatosaurus fossils were discovered by Arthur Lakes, a local miner, and his friend Henry C. Beckwith in the spring of 1877 in Morrison, a town in the eastern foothills of the Rocky Mountains in Jefferson County, Colorado. Arthur Lakes wrote to Othniel Charles Marsh, Professor of Paleontology at Yale University, and Edward Drinker Cope, a paleontologist based in Philadelphia, about the discovery until eventually collecting several fossils and sending them to both paleontologists. Marsh named Atlantosaurus montanus based on some of the fossils sent and hired Lakes to collect the rest of the material at Morrison and send it to Yale, while Cope attempted to hire Lakes as well but was rejected.Kohl, M. F., & McIntosh, J. S. 1997, Discovering Dinosaurs in the Old West: The field journals of Arthur Lakes. One of the best specimens collected by Lakes in 1877 was a well preserved partial postcranial skeleton, including many vertebrae, and a partial braincase (YPM VP 1860), which was sent to Marsh and named Apatosaurus ajax in November 1877. The composite term Apatosaurus comes from the Greek words ()/ () meaning "deception"/"deceptive", and () meaning "lizard"; thus, "deceptive lizard". Marsh gave it this name based on the chevron bones, which are dissimilar to those of other dinosaurs; instead, the chevron bones of Apatosaurus showed similarities with those of mosasaurs, most likely that of the representative species Mosasaurus. By the end of excavations at Lakes' quarry in Morrison, several partial specimens of Apatosaurus had been collected, but only the type specimen of A. ajax can be confidently referred to the species.
During excavation and transportation, the bones of the holotype skeleton were mixed with those of another Apatosaurine individual originally described as Atlantosaurus immanis; as a consequence, some elements cannot be ascribed to either specimen with confidence. Marsh distinguished the new genus Apatosaurus from Atlantosaurus on the basis of the number of sacral vertebrae, with Apatosaurus possessing three and Atlantosaurus four. Recent research shows that traits usually used to distinguish taxa at this time were actually widespread across several taxa, causing many of the taxa named to be invalid, like Atlantosaurus. Two years later, Marsh announced the discovery of a larger and more complete specimen (YPM VP 1980) from Como Bluff, Wyoming, he gave this specimen the name Brontosaurus excelsus. Also at Como Bluff, the Hubbell brothers working for Edward Drinker Cope collected a tibia, fibula, scapula, and several caudal vertebrae along with other fragments belonging to Apatosaurus in 1877–78 at Cope's Quarry 5 at the site. Later in 1884, Othniel Marsh named Diplodocus lacustris based on a chimeric partial dentary, snout, and several teeth collected by Lakes in 1877 at Morrison.Mossbrucker, M. T., & Bakker, R. T. (October 2013). Missing muzzle found: new skull material referrable to Apatosaurus ajax (Marsh 1877) from the Morrison Formation of Morrison, Colorado. In Geological Society of America Abstracts with Programs (Vol. 45, p. 111). In 2013, it was suggested that the dentary of D. lacustris and its teeth were actually from Apatosaurus ajax based on its proximity to the type braincase of A. ajax. All specimens currently considered Apatosaurus were from the Morrison Formation, the location of the excavations of Marsh and Cope.thumb|A. ajax sacrum, illustrated in 1879 |
Apatosaurus | Second Dinosaur Rush and skull issue | Second Dinosaur Rush and skull issue
After the end of the Bone Wars, many major institutions in the eastern United States were inspired by the depictions and finds by Marsh and Cope to assemble their own dinosaur fossil collections.Brinkman, P. D. (2010). The second Jurassic dinosaur rush. University of Chicago Press. The competition to mount the first sauropod skeleton specifically was the most intense, with the American Museum of Natural History, Carnegie Museum of Natural History, and Field Museum of Natural History all sending expeditions to the west to find the most complete sauropod specimen, bring it back to the home institution, and mount it in their fossil halls. The American Museum of Natural History was the first to launch an expedition, finding a well preserved skeleton (AMNH 460), which is occasionally assigned to Apatosaurus, is considered nearly complete; only the head, feet, and sections of the tail are missing, and it was the first sauropod skeleton mounted. The specimen was found north of Medicine Bow, Wyoming, in 1898 by Walter Granger, and took the entire summer to extract. To complete the mount, sauropod feet that were discovered at the same quarry and a tail fashioned to appear as Marsh believed it shouldbut which had too few vertebraewere added. In addition, a sculpted model of what the museum thought the skull of this massive creature might look like was made. This was not a delicate skull like that of Diplodocuswhich was later found to be more accuratebut was based on "the biggest, thickest, strongest skull bones, lower jaws and tooth crowns from three different quarries". These skulls were likely those of Camarasaurus, the only other sauropod for which good skull material was known at the time. The mount construction was overseen by Adam Hermann, who failed to find Apatosaurus skulls. Hermann was forced to sculpt a stand-in skull by hand. Osborn said in a publication that the skull was "largely conjectural and based on that of Morosaurus" (now Camarasaurus).thumb|left|Obsolete mount of an apatosaurine (possibly Apatosaurus) specimen AMNH460 with sculpted skull, American Museum of Natural History
In 1903, Elmer Riggs published a study that described a well-preserved skeleton of a diplodocid from the Grand River Valley near Fruita, Colorado, Field Museum of Natural History specimen P25112. Riggs thought that the deposits were similar in age to those of the Como Bluff in Wyoming from which Marsh had described Brontosaurus. Most of the skeleton was found, and after comparison with both Brontosaurus and Apatosaurus ajax, Riggs realized that the holotype of A.ajax was immature, and thus the features distinguishing the genera were not valid. Since Apatosaurus was the earlier name, Brontosaurus should be considered a junior synonym of Apatosaurus. Because of this, Riggs recombined Brontosaurus excelsus as Apatosaurus excelsus. Based on comparisons with other species proposed to belong to Apatosaurus, Riggs also determined that the Field Columbian Museum specimen was likely most similar to A.excelsus.
Despite Riggs' publication, Henry Fairfield Osborn, who was a strong opponent of Marsh and his taxa, labeled the Apatosaurus mount of the American Museum of Natural History Brontosaurus. Because of this decision the name Brontosaurus was commonly used outside of scientific literature for what Riggs considered Apatosaurus, and the museum's popularity meant that Brontosaurus became one of the best known dinosaurs, even though it was invalid throughout nearly all of the 20th and early 21st centuries.
thumb|Apatosaurine mount (FMNH P25112) in the Field Museum of Natural History in the 1950s, with its original, inaccurately reconstructed skull
It was not until 1909 that an Apatosaurus skull was found during the first expedition, led by Earl Douglass, to what would become known as the Carnegie Quarry at Dinosaur National Monument. The skull was found a short distance from a skeleton (specimen CM3018) identified as the new species Apatosaurus louisae, named after Louise Carnegie, wife of Andrew Carnegie, who funded field research to find complete dinosaur skeletons in the American West. The skull was designated CM11162; it was very similar to the skull of Diplodocus. Another smaller skeleton of A.louisae was found nearby CM11162 and CM3018. The skull was accepted as belonging to the Apatosaurus specimen by Douglass and Carnegie Museum director William H. Holland, although other scientistsmost notably Osbornrejected this identification. Holland defended his view in 1914 in an address to the Paleontological Society of America, yet he left the Carnegie Museum mount headless. While some thought Holland was attempting to avoid conflict with Osborn, others suspected Holland was waiting until an articulated skull and neck were found to confirm the association of the skull and skeleton. After Holland's death in 1934, museum staff placed a cast of a Camarasaurus skull on the mount.
While most other museums were using cast or sculpted Camarasaurus skulls on Apatosaurus mounts, the Yale Peabody Museum decided to sculpt a skull based on the lower jaw of a Camarasaurus, with the cranium based on Marsh's 1891 illustration of the skull. The skull also included forward-pointing nasalssomething unusual for any dinosaurand fenestrae differing from both the drawing and other skulls.
thumb|left|Side view of A. louisae CM3018 mounted with a cast of skull CM11162
No Apatosaurus skull was mentioned in literature until the 1970s when John Stanton McIntosh and David Berman redescribed the skulls of Diplodocus and Apatosaurus. They found that though he never published his opinion, Holland was almost certainly correct, that Apatosaurus had a Diplodocus-like skull. According to them, many skulls long thought to pertain to Diplodocus might instead be those of Apatosaurus. They reassigned multiple skulls to Apatosaurus based on associated and closely associated vertebrae. Even though they supported Holland, it was noted that Apatosaurus might have possessed a Camarasaurus-like skull, based on a disarticulated Camarasaurus-like tooth found at the precise site where an Apatosaurus specimen was found years before. On October20, 1979, after the publications by McIntosh and Berman, the first true skull of Apatosaurus was mounted on a skeleton in a museum, that of the Carnegie. In 1998, it was suggested that the Felch Quarry skull that Marsh had included in his 1896 skeletal restoration instead belonged to Brachiosaurus. This was supported in 2020 with a redescription of the brachiosaurid material found at the Felch Quarry. |
Apatosaurus | Recent discoveries and reassessment | Recent discoveries and reassessment
In 2011, the first specimen of Apatosaurus where a skull was found articulated with its cervical vertebrae was described. This specimen, CMCVP7180, was found to differ in both skull and neck features from A.louisae, but shared many features of the cervical vertebrae with A.ajax. Another well-preserved skull is Brigham Young University specimen 17096, a well-preserved skull and skeleton, with a preserved braincase. The specimen was found in Cactus Park Quarry in western Colorado. In 2013, Matthew Mossbrucker and several other authors published an abstract that described a premaxilla and maxilla from Lakes' original quarry in Morrison and referred the material to Apatosaurus ajax.
thumb|left|261x261px|Infographic explaining the history of Brontosaurus and Apatosaurus according to Tschopp etal. 2015
Almost all modern paleontologists agreed with Riggs that the two dinosaurs should be classified together in a single genus. According to the rules of the ICZN (which governs the scientific names of animals), the name Apatosaurus, having been published first, has priority as the official name; Brontosaurus was considered a junior synonym and was therefore long discarded from formal use. Despite this, at least one paleontologistRobert T. Bakkerargued in the 1990s that A.ajax and A.excelsus were in fact sufficiently distinct for the latter to merit a separate genus.
In 2015, Emanuel Tschopp, Octávio Mateus, and Roger Benson released a paper on diplodocoid systematics, and proposed that genera could be diagnosed by thirteen differing characters, and species separated based on six. The minimum number for generic separation was chosen based on the fact that A.ajax and A.louisae differ in twelve characters, and Diplodocus carnegiei and D.hallorum differ in eleven characters. Thus, thirteen characters were chosen to validate the separation of genera. The six differing features for specific separation were chosen by counting the number of differing features in separate specimens generally agreed to represent one species, with only one differing character in D.carnegiei and A.louisae, but five differing features in B.excelsus. Therefore, Tschopp etal. argued that Apatosaurus excelsus, originally classified as Brontosaurus excelsus, had enough morphological differences from other species of Apatosaurus that it warranted being reclassified as a separate genus again. The conclusion was based on a comparison of 477 morphological characteristics across 81 different dinosaur individuals. Among the many notable differences are the widerand presumably strongerneck of Apatosaurus species compared to B.excelsus. Other species previously assigned to Apatosaurus, such as Elosaurus parvus and Eobrontosaurus yahnahpin were also reclassified as Brontosaurus. Some features proposed to separate Brontosaurus from Apatosaurus include: posterior dorsal vertebrae with the centrum longer than wide; the scapula rear to the acromial edge and the distal blade being excavated; the acromial edge of the distal scapular blade bearing a rounded expansion; and the ratio of the proximodistal length to transverse breadth of the astragalus 0.55 or greater. Sauropod expert Michael D'Emic pointed out that the criteria chosen were to an extent arbitrary and that they would require abandoning the name Brontosaurus again if newer analyzes obtained different results.D'Emic, M. 2015. "Not so fast, Brontosaurus". Time.com Mammal paleontologist Donald Prothero criticized the mass media reaction to this study as superficial and premature, concluding that he would keep "Brontosaurus" in quotes and not treat the name as a valid genus.Prothero, D. 2015. "Is "Brontosaurus" Back? Not So Fast!". Skeptic.com. |
Apatosaurus | Valid species | Valid species
thumb|Apatosaurine specimen AMNH 460 at the AMNH as re-mounted in 1995
thumb|Apatosaurine mount (FMNH P25112) in the FMNH
thumb|upright|Specimen NSMT-PV 20375, National Museum of Nature and Science, which may be A.ajax or a new species
Many species of Apatosaurus have been designated from scant material. Marsh named as many species as he could, which resulted in many being based upon fragmentary and indistinguishable remains. In 2005, Paul Upchurch and colleagues published a study that analyzed the species and specimen relationships of Apatosaurus. They found that A.louisae was the most basal species, followed by FMNHP25112, and then a polytomy of A.ajax, A.parvus, and A.excelsus. Their analysis was revised and expanded with many additional diplodocid specimens in 2015, which resolved the relationships of Apatosaurus slightly differently, and also supported separating Brontosaurus from Apatosaurus.
Apatosaurus ajax was named by Marsh in 1877 after Ajax, a hero from Greek mythology. Marsh designated the incomplete, juvenile skeleton YPM1860 as its holotype. The species is less studied than Brontosaurus and A.louisae, especially because of the incomplete nature of the holotype. In 2005, many specimens in addition to the holotype were found assignable to A.ajax, YPM1840, NSMT-PV 20375, YPM1861, and AMNH460. The specimens date from the late Kimmeridgian to the early Tithonian ages. In 2015, only the A.ajax holotype YPM1860 assigned to the species, with AMNH460 found either to be within Brontosaurus, or potentially its own taxon. However, YPM1861 and NSMT-PV 20375 only differed in a few characteristics, and cannot be distinguished specifically or generically from A.ajax. YPM1861 is the holotype of "Atlantosaurus" immanis, which means it might be a junior synonym of A.ajax.
Apatosaurus louisae was named by Holland in 1916, being first known from a partial skeleton that was found in Utah. The holotype is CM3018, with referred specimens including CM3378, CM11162, and LACM52844. The former two consist of a vertebral column; the latter two consist of a skull and a nearly complete skeleton, respectively. Apatosaurus louisae specimens all come from the late Kimmeridgian of Dinosaur National Monument. In 2015, Tschopp etal. found the type specimen of Apatosaurus laticollis to nest closely with CM3018, meaning the former is likely a junior synonym of A.louisae.
The cladogram below is the result of an analysis by Tschopp, Mateus, and Benson (2015). The authors analyzed most diplodocid type specimens separately to deduce which specimen belonged to which species and genus. |
Apatosaurus | Reassigned species | Reassigned species
thumb|The most complete specimen known to date, A. sp. BYU 17096 nicknamed "Einstein"
Apatosaurus grandis was named in 1877 by Marsh in the article that described A.ajax. It was briefly described, figured, and diagnosed. Marsh later mentioned it was only provisionally assigned to Apatosaurus when he reassigned it to his new genus Morosaurus in 1878. Since Morosaurus has been considered a synonym of Camarasaurus, C.grandis is the oldest-named species of the latter genus.
Apatosaurus excelsus was the original type species of Brontosaurus, first named by Marsh in 1879. Elmer Riggs reclassified Brontosaurus as a synonym of Apatosaurus in 1903, transferring the species B.excelsus to A.excelsus. In 2015, Tschopp, Mateus, and Benson argued that the species was distinct enough to be placed in its own genus, so they reclassified it back into Brontosaurus.
Apatosaurus parvus, first described from a juvenile specimen as Elosaurus in 1902 by Peterson and Gilmore, was reassigned to Apatosaurus in 1994, and then to Brontosaurus in 2015. Many other, more mature specimens were assigned to it following the 2015 study.
Apatosaurus minimus was originally described as a specimen of Brontosaurus sp. in 1904 by Osborn. In 1917, Henry Mook named it as its own species, A.minimus, for a pair of ilia and their sacrum. In 2012, Mike P. Taylor and Matt J. Wedel published a short abstract describing the material of A. minimus, finding it hard to place among either Diplodocoidea or Macronaria. While it was placed with Saltasaurus in a phylogenetic analysis, it was thought to represent instead some form with convergent features from many groups. The study of Tschopp etal. did find that a camarasaurid position for the taxon was supported, but noted that the position of the taxon was found to be highly variable and there was no clearly more likely position.
Apatosaurus alenquerensis was named in 1957 by Albert-Félix de Lapparent and Georges Zbyweski. It was based on post cranial material from Portugal. In 1990, this material was reassigned to Camarasaurus, but in 1998 it was given its own genus, Lourinhasaurus. This was further supported by the findings of Tschopp etal. in 2015, where Lourinhasaurus was found to be sister to Camarasaurus and other camarasaurids.
Apatosaurus yahnahpin was named by James Filla and Patrick Redman in 1994. Bakker made A.yahnahpin the type species of a new genus, Eobrontosaurus in 1998, and Tschopp reclassified it as Brontosaurus yahnahpin in 2015. |
Apatosaurus | Classification | Classification
thumb|upright|Shoulder blade and coracoid of A. ajax
Apatosaurus is a member of the family Diplodocidae, a clade of gigantic sauropod dinosaurs. The family includes some of the longest creatures ever to walk the earth, including Diplodocus, Supersaurus, and Barosaurus. Apatosaurus is sometimes classified in the subfamily Apatosaurinae, which may also include Suuwassea, Supersaurus, and Brontosaurus. Othniel Charles Marsh described Apatosaurus as allied to Atlantosaurus within the now-defunct group Atlantosauridae. In 1878, Marsh raised his family to the rank of suborder, including Apatosaurus, Atlantosaurus, Morosaurus (=Camarasaurus) and Diplodocus. He classified this group within Sauropoda, a group he erected in the same study. In 1903, Elmer S. Riggs said the name Sauropoda would be a junior synonym of earlier names; he grouped Apatosaurus within Opisthocoelia. Sauropoda is still used as the group name. In 2011, John Whitlock published a study that placed Apatosaurus a more basal diplodocid, sometimes less basal than Supersaurus.
Cladogram of the Diplodocidae after Tschopp, Mateus, and Benson (2015). |
Apatosaurus | Paleobiology | Paleobiology
thumb|Tracks of a juvenile
It was believed throughout the 19th and early 20th centuries that sauropods like Apatosaurus were too massive to support their own weight on dry land. It was theorized that they lived partly submerged in water, perhaps in swamps. More recent findings do not support this; sauropods are now thought to have been fully terrestrial animals. A study of diplodocid snouts showed that the square snout, large proportion of pits, and fine, subparallel scratches of the teeth of Apatosaurus suggests it was a ground-height, nonselective browser. It may have eaten ferns, cycadeoids, seed ferns, horsetails, and algae. Stevens and Parish (2005) speculate that these sauropods fed from riverbanks on submerged water plants.
A 2015 study of the necks of Apatosaurus and Brontosaurus found many differences between them and other diplodocids, and that these variations may have shown that the necks of Apatosaurus and Brontosaurus were used for intraspecific combat. Various uses for the single claw on the forelimb of sauropods have been proposed. One suggestion is that they were used for defense, but their shape and size make this unlikely. It was also possible they were for feeding, but the most probable use for the claw was grasping objects such as tree trunks when rearing.
Trackways of sauropods like Apatosaurus show that they may have had a range of around per day, and that they could potentially have reached a top speed of per hour. The slow locomotion of sauropods may be due to their minimal muscling, or to recoil after strides. A trackway of a juvenile has led some to believe that they were capable of bipedalism, though this is disputed. |
Apatosaurus | Neck posture | Neck posture
thumb|Artistic interpretation of an individual of A. louisae arching its neck down to drink
Diplodocids like Apatosaurus are often portrayed with their necks held high up in the air, allowing them to browse on tall trees. Some studies state diplodocid necks were less flexible than previously believed, because the structure of the neck vertebrae would not have allowed the neck to bend far upward, and that sauropods like Apatosaurus were adapted to low browsing or ground feeding.
Other studies by Taylor find that all tetrapods appear to hold their necks at the maximum possible vertical extension when in a normal, alert posture; they argue the same would hold true for sauropods barring any unknown, unique characteristics that set the soft tissue anatomy of their necks apart from that of other animals. Apatosaurus, like Diplodocus, would have held its neck angled upward with the head pointing downward in a resting posture. Kent Stevens and Michael Parrish (1999 and 2005) state Apatosaurus had a great feeding range; its neck could bend into a U-shape laterally. The neck's range of movement would have also allowed the head to feed at the level of the feet.
Matthew Cobley et al. (2013) dispute this, finding that large muscles and cartilage would have limited movement of the neck. They state the feeding ranges for sauropods like Diplodocus were smaller than previously believed, and the animals may have had to move their whole bodies around to better access areas where they could browse vegetation. As such, they might have spent more time foraging to meet their minimum energy needs. The conclusions of Cobley etal. are disputed by Taylor, who analyzed the amount and positioning of intervertebral cartilage to determine the flexibility of the neck of Apatosaurus and Diplodocus. He found that the neck of Apatosaurus was very flexible. |
Apatosaurus | Physiology | Physiology
thumb|Tail vertebrae of specimen FMNH P25112, showing pneumatic fossae (holes)
Given the large body mass and long neck of sauropods like Apatosaurus, physiologists have encountered problems determining how these animals breathed. Beginning with the assumption that, like crocodilians, Apatosaurus did not have a diaphragm, the dead-space volume (the amount of unused air remaining in the mouth, trachea, and air tubes after each breath) has been estimated at for a specimen. Paladino calculates its tidal volume (the amount of air moved in or out during a single breath) at with an avian respiratory system, if mammalian, and if reptilian.
On this basis, its respiratory system would likely have been parabronchi, with multiple pulmonary air sacs as in avian lungs, and a flow-through lung. An avian respiratory system would need a lung volume of about compared with a mammalian requirement of , which would exceed the space available. The overall thoracic volume of Apatosaurus has been estimated at , allowing for a , four-chambered heart and a lung capacity. That would allow about for the necessary tissue. Evidence for the avian system in Apatosaurus and other sauropods is also present in the pneumaticity of the vertebrae. Though this plays a role in reducing the weight of the animal, Wedel (2003) states they are also likely connected to air sacs, as in birds.
James Spotila et al. (1991) concludes that the large body size of sauropods would have made them unable to maintain high metabolic rates because they would not have been able to release enough heat. They assumed sauropods had a reptilian respiratory system. Wedel says that an avian system would have allowed it to dump more heat. Some scientists state that the heart would have had trouble sustaining sufficient blood pressure to oxygenate the brain. Others suggest that the near-horizontal posture of the head and neck would have eliminated the problem of supplying blood to the brain because it would not have been elevated.
James Farlow (1987) calculates that an Apatosaurus-sized dinosaur about would have possessed of fermentation contents, though he cautions that the regression equation being used is based on living mammals which are much smaller and physiologically different. Assuming Apatosaurus had an avian respiratory system and a reptilian resting-metabolism, Frank Paladino etal. (1997) estimate the animal would have needed to consume only about of water per day. |
Apatosaurus | Growth | Growth
thumb|left|Juvenile A. sp. mount, Sam Noble Oklahoma Museum of Natural History
A 1999 microscopic study of Apatosaurus and Brontosaurus bones concluded the animals grew rapidly when young and reached near-adult sizes in about 10years. In 2008, a study on the growth rates of sauropods was published by Thomas Lehman and Holly Woodward. They said that by using growth lines and length-to-mass ratios, Apatosaurus would have grown to 25t (25 long tons; 28 short tons) in 15years, with growth peaking at in a single year. An alternative method, using limb length and body mass, found Apatosaurus grew per year, and reached its full mass before it was about 70years old. These estimates have been called unreliable because the calculation methods are not sound; old growth lines would have been obliterated by bone remodeling. One of the first identified growth factors of Apatosaurus was the number of sacral vertebrae, which increased to five by the time of the creature's maturity. This was first noted in 1903 and again in 1936.
Long-bone histology enables researchers to estimate the age that a specific individual reached. A study by Eva Griebeler etal. (2013) examined long-bone histological data and concluded the Apatosaurus sp.SMA0014 weighed , reached sexual maturity at 21years, and died aged 28. The same growth model indicated Apatosaurus sp.BYU 601–17328 weighed , reached sexual maturity at 19years, and died aged 31. |
Apatosaurus | Juveniles | Juveniles
Compared with most sauropods, a relatively large amount of juvenile material is known from Apatosaurus. Multiple specimens in the OMNH are from juveniles of an undetermined species of Apatosaurus; this material includes partial shoulder and pelvic girdles, some vertebrae, and limb bones. OMNH juvenile material is from at least two different age groups and based on overlapping bones likely comes from more than three individuals. The specimens exhibit features that distinguish Apatosaurus from its relatives, and thus likely belong to the genus. Juvenile sauropods tend to have proportionally shorter necks and tails, and a more pronounced forelimb-hindlimb disparity than found in adult sauropods. |
Apatosaurus | Tail | Tail
thumb|left|Skeletal diagram of A. louisae, showing the long, tapering tail
An article published in 1997 reported research of the mechanics of Apatosaurus tails by Nathan Myhrvold and paleontologist Philip J. Currie. Myhrvold carried out a computer simulation of the tail, which in diplodocids like Apatosaurus was a very long, tapering structure resembling a bullwhip. This computer modeling suggested diplodocids were capable of producing a whiplike cracking sound of over 200 decibels, comparable to the volume of a cannon being fired.
A pathology has been identified on the tail of Apatosaurus, caused by a growth defect. Two caudal vertebrae are seamlessly fused along the entire articulating surface of the bone, including the arches of the neural spines. This defect might have been caused by the lack or inhibition of the substance that forms intervertebral disks or joints. It has been proposed that the whips could have been used in combat and defense, but the tails of diplodocids were quite light and narrow compared to Shunosaurus and mamenchisaurids, and thus to injure another animal with the tail would severely injure the tail itself. More recently, Baron (2020) considers the use of the tail as a bullwhip unlikely because of the potentially catastrophic muscle and skeletal damage such speeds could cause on the large and heavy tail. Instead, he proposes that the tails might have been used as a tactile organ to keep in touch with the individuals behind and on the sides in a group while migrating, which could have augmented cohesion and allowed communication among individuals while limiting more energetically demanding activities like stopping to search for dispersed individuals, turning to visually check on individuals behind, or communicating vocally. |
Apatosaurus | Paleoecology | Paleoecology
thumb|upright|Allosaurus and A. sp., Sam Noble Oklahoma Museum of Natural History
The Morrison Formation is a sequence of shallow marine and alluvial sediments which, according to radiometric dating, dates from between 156.3mya at its base, and 146.8mya at the top, placing it in the late Oxfordian, Kimmeridgian, and early Tithonian stages of the Late Jurassic period. This formation is interpreted as originating in a locally semiarid environment with distinct wet and dry seasons. The Morrison Basin, where dinosaurs lived, stretched from New Mexico to Alberta and Saskatchewan; it was formed when the precursors to the Front Range of the Rocky Mountains started pushing up to the west. The deposits from their east-facing drainage basins were carried by streams and rivers and deposited in swampy lowlands, lakes, river channels, and floodplains. This formation is similar in age to the Lourinhã Formation in Portugal and the Tendaguru Formation in Tanzania.
thumb|left|Ischium of an Apatosaurus showing bite marks from a large theropod
Apatosaurus was the second most common sauropod in the Morrison Formation ecosystem, after Camarasaurus. Apatosaurus may have been more solitary than other Morrison Formation dinosaurs. Fossils of the genus have only been found in the upper levels of the formation. Those of Apatosaurus ajax are known exclusively from the upper Brushy Basin Member, about 152–151 mya. A.louisae fossils are rare, known only from one site in the upper Brushy Basin Member; they date to the late Kimmeridgian stage, about 151mya. Additional Apatosaurus remains are known from similarly aged or slightly younger rocks, but they have not been identified as any particular species, and thus may instead belong to Brontosaurus.
The Morrison Formation records a time when the local environment was dominated by gigantic sauropod dinosaurs. Dinosaurs known from the Morrison Formation include the theropods Allosaurus, Ceratosaurus, Ornitholestes, and Torvosaurus; the sauropods Brontosaurus, Brachiosaurus, Camarasaurus, and Diplodocus; and the ornithischians Camptosaurus, Dryosaurus, and Stegosaurus. Apatosaurus is commonly found at the same sites as Allosaurus, Camarasaurus, Diplodocus, and Stegosaurus. Allosaurus accounted for 70–75% of theropod specimens and was at the top trophic level of the Morrison food web. Many of the dinosaurs of the Morrison Formation are of the same genera as those seen in Portuguese rocks of the Lourinhã Formationmainly Allosaurus, Ceratosaurus, and Torvosaurusor have a close counterpartBrachiosaurus and Lusotitan, Camptosaurus and Draconyx, and Apatosaurus and Dinheirosaurus. Other vertebrates that are known to have shared this paleo-environment include ray-finned fishes, frogs, salamanders, turtles, sphenodonts, lizards, terrestrial and aquatic crocodylomorphs, and several species of pterosaur. Shells of bivalves and aquatic snails are also common. The flora of the period has been evidenced in fossils of green algae, fungi, mosses, horsetails, cycads, ginkgoes, and several families of conifers. Vegetation varied from river-lining forests of tree ferns with fern understory (gallery forests), to fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum. |
Apatosaurus | References | References |
Apatosaurus | External links | External links
Batuman, Elif. Brontosaurus Rising (April 2015), The New Yorker
Krystek, Lee. "Whatever Happened to the Brontosaurus?" UnMuseum (Museum of Unnatural Mystery), 2002.
Taylor, Mike. "Why is 'Brontosaurus' now called Apatosaurus?" MikeTaylor.org.uk, June 28, 2004.
Category:Diplodocidae
Category:Dinosaur genera
Category:Kimmeridgian dinosaurs
Category:Morrison Formation
Category:Dinosaurs of the United States
Category:Fossil taxa described in 1877
Category:Taxa named by Othniel Charles Marsh |
Apatosaurus | Table of Content | short description, Description, Discovery and species, Initial discovery, Second Dinosaur Rush and skull issue, Recent discoveries and reassessment, Valid species, Reassigned species, Classification, Paleobiology, Neck posture, Physiology, Growth, Juveniles, Tail, Paleoecology, References, External links |
Allosaurus | mergefrom | Allosaurus () is an extinct genus of large theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic period (Kimmeridgian to late Tithonian ages). The name "Allosaurus" means "different lizard", alluding to its unique (at the time of its discovery) concave vertebrae. The first fossil remains that could definitively be ascribed to this genus were described in 1877 by Othniel Charles Marsh. The genus has a very complicated taxonomy and includes at least three valid species, the best known of which is A. fragilis. The bulk of Allosaurus remains have come from North America's Morrison Formation, with material also known from the Alcobaça Formation and Lourinhã Formation in Portugal with teeth known from Germany. It was known for over half of the 20th century as Antrodemus, but a study of the abundant remains from the Cleveland-Lloyd Dinosaur Quarry returned the name "Allosaurus" to prominence. As one of the first well-known theropod dinosaurs, it has long attracted attention outside of paleontological circles.
Allosaurus was a large bipedal predator for its time. Its skull was light, robust, and equipped with dozens of sharp, serrated teeth. It averaged in length for A. fragilis, with the largest specimens estimated as being long. Relative to the large and powerful legs, its three-fingered hands were small and the body was balanced by a long, muscular tail. It is classified in the family Allosauridae. As the most abundant large predator of the Morrison Formation, Allosaurus was at the top of the food chain and probably preyed on large herbivorous dinosaurs such as ornithopods, stegosaurids, and sauropods. It is also possible that it hunted other predators. Scientists have debated whether Allosaurus had cooperative social behavior and hunted in packs or was a solitary predator that form congregations, with evidence supporting either side. |
Allosaurus | Discovery and history | Discovery and history |
Allosaurus | Early discoveries and research | Early discoveries and research
The discovery and early study of Allosaurus is complicated by the multiplicity of names coined during the Bone Wars of the late 19th century. The first described fossil in this history was a bone obtained secondhand by Ferdinand Vandeveer Hayden in 1869. It came from Middle Park, near Granby, Colorado, probably from Morrison Formation rocks. The locals had identified such bones as "petrified horse hoofs". Hayden sent his specimen to Joseph Leidy, who identified it as half of a tail vertebra and tentatively assigned it to the European dinosaur genus Poekilopleuron as Poicilopleuron valens. He later decided it deserved its own genus, Antrodemus.
Allosaurus itself is based on YPM 1930, a small collection of fragmentary bones including parts of three vertebrae, a rib fragment, a tooth, a toe bone, and (most useful for later discussions) the shaft of the right humerus (upper arm). Othniel Charles Marsh gave these remains the formal name Allosaurus fragilis in 1877. Allosaurus comes from the Greek words /, meaning "strange" or "different", and /, meaning "lizard" or "reptile". It was named 'different lizard' because its vertebrae were different from those of other dinosaurs known at the time of its discovery. The species epithet fragilis is Latin for "fragile", referring to lightening features in the vertebrae. The bones were collected from the Morrison Formation of Garden Park, north of Cañon City. O. C. Marsh and Edward Drinker Cope, who were in scientific competition with each other, went on to coin several other genera based on similarly sparse material that would later figure in the taxonomy of Allosaurus. These include Marsh's Creosaurus and Labrosaurus, as well as Cope's Epanterias.
In their haste, Cope and Marsh did not always follow up on their discoveries (or, more commonly, those made by their subordinates). For example, after the discovery by Benjamin Mudge of the type specimen of Allosaurus in Colorado, Marsh elected to concentrate work in Wyoming. When work resumed at Garden Park in 1883, M. P. Felch found an almost complete Allosaurus and several partial skeletons. In addition, one of Cope's collectors, H. F. Hubbell, found a specimen in the Como Bluff area of Wyoming in 1879, but apparently did not mention its completeness and Cope never unpacked it. Upon unpacking it in 1903 (several years after Cope had died), it was found to be one of the most complete theropod specimens then known and the skeleton, now cataloged as AMNH 5753, was put on public view in 1908. This is the well-known mount poised over a partial Apatosaurus skeleton as if scavenging it, illustrated as such in a painting by Charles R. Knight. Although notable as the first free-standing mount of a theropod dinosaur and often illustrated and photographed, it has never been scientifically described.
The multiplicity of early names complicated later research, with the situation compounded by the terse descriptions provided by Marsh and Cope. Even at the time, authors such as Samuel Wendell Williston suggested that too many names had been coined. For example, Williston pointed out in 1901 that Marsh had never been able to adequately distinguish Allosaurus from Creosaurus. The most influential early attempt to sort out the convoluted situation was produced by Charles W. Gilmore in 1920. He came to the conclusion that the tail vertebra named Antrodemus by Leidy was indistinguishable from those of Allosaurus and that Antrodemus should be the preferred name because, as the older name, it had priority. Antrodemus became the accepted name for this familiar genus for over 50 years, until James Henry Madsen published on the Cleveland-Lloyd specimens and concluded that Allosaurus should be used because Antrodemus was based on material with poor, if any, diagnostic features and locality information. For example, the geological formation that the single bone of Antrodemus came from is unknown. "Antrodemus" has been used informally for convenience when distinguishing between the skull Gilmore restored and the composite skull restored by Madsen. |
Allosaurus | Cleveland-Lloyd discoveries | Cleveland-Lloyd discoveries
thumb|A. fragilis at the Cleveland-Lloyd Dinosaur Quarry museum, Utah
Although sporadic work at what became known as the Cleveland-Lloyd Dinosaur Quarry in Emery County, Utah, had taken place as early as 1927 and the fossil site itself described by William L. Stokes in 1945, major operations did not begin there until 1960. Under a cooperative effort involving nearly 40 institutions, thousands of bones were recovered between 1960 and 1965, led by James Henry Madsen. The quarry is notable for the predominance of Allosaurus remains, the condition of the specimens, and the lack of scientific resolution on how it came to be. The majority of bones belong to the large theropod Allosaurus fragilis (it is estimated that the remains of at least 46 A. fragilis have been found there, out of at a minimum 73 dinosaurs) and the fossils found there are disarticulated and well-mixed. Nearly a dozen scientific papers have been written on the taphonomy of the site, suggesting numerous mutually exclusive explanations for how it may have formed. Suggestions have ranged from animals getting stuck in a bog, becoming trapped in deep mud, falling victim to drought-induced mortality around a waterhole, and getting trapped in a spring-fed pond or seep. Regardless of the actual cause, the great quantity of well-preserved Allosaurus remains has allowed this genus to be known in great detail, making it among the best-known of all theropods. Skeletal remains from the quarry pertain to individuals of almost all ages and sizes, from less than to long, and the disarticulation is an advantage for describing bones usually found fused. Due to being one of Utah's two fossil quarries where numerous Allosaurus specimens have been discovered, Allosaurus was designated as the state fossil of Utah in 1988. |
Allosaurus | Modern study | Modern study
The period since Madsen's monograph has been marked by a great expansion in studies dealing with topics concerning Allosaurus in life (paleobiological and paleoecological topics). Such studies have covered topics including skeletal variation, growth, skull construction, hunting methods, the brain, and the possibility of gregarious living and parental care. Reanalysis of old material (particularly of large 'allosaur' specimens), new discoveries in Portugal, and several very complete new specimens have also contributed to the growing knowledge base. |
Allosaurus | "Big Al" and "Big Al II" | "Big Al" and "Big Al II"
left|thumb|"Big Al" A. jimmadseni skeleton at the Museum of the Rockies
In 1991, "Big Al" (MOR 693), a 95% complete, partially articulated specimen of Allosaurus was discovered, measuring about long. MOR 693 was excavated near Shell, Wyoming, by a joint Museum of the Rockies and University of Wyoming Geological Museum team. This skeleton was discovered by a Swiss team, led by Kirby Siber. Chure and Loewen in 2020 identified the individual as a representative of the species A. jimmadseni. In 1996, the same team discovered a second Allosaurus, "Big Al II". This specimen, the best preserved skeleton of its kind to date, is also referred to A. jimmadseni.
The completeness, preservation, and scientific importance of this skeleton gave "Big Al" its name. The individual itself was below the average size for Allosaurus fragilis, as it was a subadult estimated at only 87% grown. The specimen was described by Breithaupt in 1996. Nineteen of its bones were broken or showed signs of serious infection, which may have contributed to "Big Al's" death. Pathologic bones included five ribs, five vertebrae, and four bones of the feet. Several of its damaged bones showed signs of osteomyelitis, a severe bone infection. A particular problem for the living animal was infection and trauma to the right foot that probably affected movement and may have also predisposed the other foot to injury because of a change in gait. "Big Al" had an infection on the first phalanx on the third toe that was afflicted by an involucrum. The infection was long-lived, perhaps up to six months. "Big Al II" is also known to have multiple injuries. |
Allosaurus | Portuguese discoveries | Portuguese discoveries
thumb|right|Cliffs of Lourinhã Formation outcrops, Portugal
In 1988, during construction works of a warehouse, a skeleton of a large theropod was discovered near the village of Andrés, Leiria District, Portugal. The Andrés quarry is included in the Bombarral Formation ("Grés Superiores"). The lower part of this formation is diachronic with the Alcobaça Formation in the northen Lusitanian Basin, and is dated to the Early Tithonian. This specimen was reported in 1999 as the first occurrence of Allosaurus fragilis outside North America. The specimen, labeled MNHNUL/AND.001, is deposited in the National Museum of Natural History and Science, Lisbon. It consists of a partial skeleton, composed of an incomplete right quadrate, several vertebrae and chevrons, several dorsal ribs and gastralia, a partial pelvis, most of the hind limbs and several indeterminate fragments. In 2003, Miguel Telles Antunes and Octávio Mateus published a review of the dinosaurs from Portugal, where they assigned the Andrés specimen to Allosaurus sp.
The Guimarota coal mine in Leiria, Portugal, produced plenty of remains of micro-vertebrates while it was being explored.Martin, T. & Krebs, B. 2000 Guimarota. A Jurassic ecosystem. Munich: Dr Friedrich Pfeil. The Guimarota beds belong to the Alcobaça Formation, and are dated of the Late Kimmeridgian. In 2005, Oliver Rauhut and Regina Fechner describe the right maxilla of a juvenile theropod (IPFUB Gui Th 4) from the Guimarota mine, that was stored in the collections of the Institute of Geological Sciences of the Free University of Berlin. They attribute the maxilla to Allosaurus sp. based on the large maxillary fenestra and coeval presence of the other Allosaurus specimens. This specimen allowed the authors to conclude that the development of paranasal pneumacity in theropods is heterochronic, with juveniles having more pronouced pneumaticity than adults.
In 2006, a new species of Allosaurus, A. europaeus, was reported based a specimen found in a beach near Vale Frades, Lourinhã, Portugal. The specimen, labeled ML415, is deposited in the Lourinhã Museum, and consists of a partial skull, three cervical vertebrae and cervical ribs. It was found in rocks of the Praia Azul Member of the Lourinhã Formation, which in that sector is dated to the Early Tithonian.
In 2005, the Andrés quarry was reactivated for further prospection, which yielded remains of a diverse vertebrate fauna and new Allosaurus remains. These new remains (such as a partial right frontal, MNHNUL/AND.001/062), along with further preparation of the original Andrés specimen, allowed for a more detailed comparison with other Allosaurus species. The authors concluded that the Andrés specimen is compatible with the diagnosis of A. fragilis, and also disputed the attribution of the Vale Frades specimen to a new species, claiming that the autapomorphies proposed in the diagnosis of A. europaeus can be explained by individual variation. In 2010, new Allosaurus elements from the Andrés quarry are reported, including new cranial remains such as a right quadrate-quadratojudal, two lacrimals, a right dentary, a right frontal, the posterior end of the right mandible and a complete braincase. A second complete left ilium suggests the presence of a second Allosaurus individual in the quarry, larger than the first. The authors once again claim that A. europaeus should be considered a nomen dubium until a more detailed description of the Vale Frades specimen is published.
A detailed description of the remains of the Andrés specimen was published on the doctoral thesis of Elisabete Malafaia.Malafaia, E. (2017). Phylogenetic analysis, paleoenvironmental and paleobiogeographic interpretation of theropod dinosaurs from the Upper Jurassic of the Lusitanian Basin [Doctoral Thesis, Universidade de Lisboa]. https://repositorio.ulisboa.pt/handle/10451/35031 The remains were collected between 1988 and 2010, and include cranial elements (such as the maxilla, nasal, lacrimals, prefrontal, postorbitals, frontals, palatines, quadrate, quadratojugal, squamosal, vomer, braincase, articular, surangulars, prearticular, angulars, supradentary and coronoid, isolated mesial and lateral teeth) and postcranial elements (intercentrum of the atlas, dorsal, sacral and caudal vertebrae, cervical and dorsal ribs, chevrons, coracoid, ilium, pubes, femora, tibiae, fibulae, astragalus and calcaneum, distal tarsal III, second, tird, and fourth metatarsals, and several phalanges). Duplicate elements reported in the thesis include the previously mentioned left ilium, a fragmentary pubic peduncle in articulation with the pubes, and a right frontal, caudal vertebra, and pedal phalanges of a third much smaller individual. The author claims that the Andrés specimens present noticeable differences with both A. fragilis and the type specimen of A. europaeus, but tentatively assigns it to Allosaurus cf. europaeus, pending the discovery of more specimens that allow the comparison between the two.
In 2024, Burigo and Mateus publish a redescription and revised diagnosis of the Vale Frades specimen. The authors report new elements, such as the atlas-axis, coronoid, new teeth and rib fragments, and confirm the validity of the species. A specimen-level phylogenetic analysis using scored cranial characters was performed. The authors claim that the Andrés specimen is attributable to A. europaeus, and that A. europaeus is more closely related to A. jimmadsenni than to A. fragilis. |
Allosaurus | Species | Species
thumb|upright|Diagram comparing skulls of three recognized species; A. fragilis (A), A. jimmadseni (B), A. europaeus (C)
Seven species of Allosaurus have been named: A. anax, A. amplus, A. atrox, A. europaeus, the type species A. fragilis, A. jimmadseni and A. lucasi. Among these (excluding A. anax, which was named in 2024), Daniel Chure and Mark Loewen in 2020 only recognized the species A. fragilis, A. europaeus, and the newly-named A. jimmadseni as being valid species. Some studies have suggested that A. europaeus does not show any unique characters compared to the North American species, though other authors have suggested that the species is valid and has a number of distinguishing characters.
A. fragilis is the type species and was named by Marsh in 1877. It is known from the remains of at least 60 individuals, all found in the Kimmeridgian–Tithonian Upper Jurassic-age Morrison Formation of the United States, spread across Colorado, Montana, New Mexico, Oklahoma, South Dakota, Utah, and Wyoming. Details of the humerus (upper arm) of A. fragilis have been used as diagnostic among Morrison theropods, but A. jimmadseni indicates that this is no longer the case at the species level.
A. jimmadseni has been scientifically described based on two nearly complete skeletons. The first specimen to wear the identification was unearthed in Dinosaur National Monument in northeastern Utah, with the original "Big Al" individual subsequently recognized as belonging to the same species. This species differs from A. fragilis in several anatomical details, including a jugal (cheekbone) with a straight lower margin. Fossils are confined to the Salt Wash Member of the Morrison Formation, with A. fragilis only found in the higher Brushy Basin Member. However, stratigraphic work done by Suzannah Maidment found that both species were actually coeval and were instead segregated by geography, with A. fragilis mostly found in the southern parts of the Morrison Formation, while A. jimmadseni is largely found in the northern parts.
The specific name jimmadseni is named in honor of Madsen, for his contributions to the taxonomy of the genus, notably for his 1976 work.
thumb|left|upright=0.9|Holotype postorbital of A. anax
A. fragilis, A. jimmadseni, A. anax, A. amplus, and A. lucasi are all known from remains discovered in the Kimmeridgian–Tithonian Upper Jurassic-age Morrison Formation of the United States, spread across Colorado, Montana, New Mexico, Oklahoma, South Dakota, Utah and Wyoming. A. fragilis is regarded as the most common, known from the remains of at least 60 individuals. For a while in the late 1980s and early 1990s, it was common to recognize A. fragilis as the short-snouted species, with the long-snouted taxon being A. atrox. However, subsequent analysis of specimens from the Cleveland-Lloyd Dinosaur Quarry, Como Bluff, and Dry Mesa Quarry showed that the differences seen in the Morrison Formation material could be attributed to individual variation. A study of skull elements from the Cleveland-Lloyd site found wide variation between individuals, calling into question previous species-level distinctions based on such features as the shape of the lacrimal horns and the proposed differentiation of A. jimmadseni based on the shape of the jugal. A. anax was described and named in 2024 from several fossils representing various skeleton parts, the holotype being a postorbital numbered as OMNH 1771. This species is characterized by the lack of rugose ornamentation on the postorbital, the dorsal vertebrae with hourglass-shaped centra and pneumatic foramina, and other features of the postorbital, cervical vertebrae, and fibula. The specific name comes from the Ancient Greek ἄναξ (anax, "king", "lord" or "tribal chief"), and is intended to be an updated reference to the now dubious saurischian genus Saurophaganax, to which the fossils were previously attributed.
The Allosaurus material from Portugal has a controversial taxonomic research history. The Andrés Allosaurus specimens, consisting of very complete cranial and post-cranial remains, have been attributed to A. fragilis,Dantas, P., Pérez-Moreno, B., Chure, D., Silva, C. M. da, Santos, V. F., Póvoas, L., Cachão, M., Sanz, J., Pires, C., Bruno, G., Ramalheiro, G., & Galopim De Carvalho, A. M. (1999). O dinossáurio carnívoro Allosaurus fragilis no Jurássico superior português. Al-Madan, 8, 23–28. https://doi.org/10.13140/RG.2.1.3224.1762 A. sp, A. europaeus and A. cf. europaeus. The Vale Frades Allosaurus, consisting of a partial skull and cervical vertebrae and ribs, is the type specimen of A. europaeus, although the validity of that species has been previously questioned. In 2024, a revised diagnosis of A. europaeus was published, confirming the validity of the species. The specific affinities of the Andrés specimens are still unclear.
The issue of species and potential synonyms was historically complicated by the type specimen of Allosaurus fragilis (YPM 1930) being extremely fragmentary, consisting of a few incomplete vertebrae, limb fragments, rib fragments, and a single tooth. Because of this, several scientists have interpreted the type specimen as potentially dubious, meaning the genus Allosaurus itself or at least the species A. fragilis would be a nomen dubium ("dubious name", based on a specimen too incomplete to compare to other specimens or to classify). To address this situation, Gregory S. Paul and Kenneth Carpenter (2010) submitted a petition to the ICZN to have the name A. fragilis officially transferred to the more complete specimen USNM 4734 (as a neotype), a decision that was ratified by the ICZN on December 29, 2023.
Teeth of indeterminate species of Allosaurus have been reported from Tönniesberg and Kahlberg in Saxony, Germany, dating to the upper Kimmeridigian. |
Allosaurus | Synonyms | Synonyms
thumb|Holotype material of Creosaurus atrox
Creosaurus, Epanterias, and Labrosaurus are provisionally regarded as junior synonyms of Allosaurus, though the latter two require new analyses to clarify their specific status. Most of the species that are regarded as synonyms of A. fragilis, or that were misassigned to the genus, are obscure and based on very scrappy remains. One exception is Labrosaurus ferox, named in 1884 by Marsh for an oddly formed partial lower jaw, with a prominent gap in the tooth row at the tip of the jaw, and a rear section greatly expanded and turned down. Later researchers suggested that the bone was pathologic, showing an injury to the living animal, and that part of the unusual form of the rear of the bone was due to plaster reconstruction. It is now regarded as an example of A. fragilis.
In his 1988 book, Predatory Dinosaurs of the World, the freelance artist & author Gregory S. Paul proposed that A. fragilis had tall pointed horns and a slender build compared to a postulated second species A. atrox, as well as not being a different sex due to rarity. Allosaurus atrox was originally named by Marsh in 1878 as the type species of its own genus, Creosaurus, and is based on YPM 1890, an assortment of bones that includes a couple of pieces of the skull, portions of nine tail vertebrae, two hip vertebrae, an ilium, and ankle and foot bones. Although the idea of two common Morrison allosaur species was followed in some semi-technical and popular works, the 2000 thesis on Allosauridae noted that Charles Gilmore mistakenly reconstructed USNM 4734 as having a shorter skull than the specimens referred by Paul to atrox, refuting supposed differences between USNM 4734 and putative A. atrox specimens like DINO 2560, AMNH 600, and AMNH 666.
"Allosaurus agilis", seen in Zittel, 1887, and Osborn, 1912, is a typographical error for A. fragilis. "Allosaurus ferox" is a typographical error by Marsh for A. fragilis in a figure caption for the partial skull YPM 1893 and YPM 1893 has been treated as a specimen of A fragilis. Likewise, "Labrosaurus fragilis" is a typographical error by Marsh (1896) for Labrosaurus ferox. "A. whitei" is a nomen nudum coined by Pickering in 1996 for the complete Allosaurus specimens that Paul referred to A. atrox.
"Madsenius" was coined by David Lambert in 1990, being based on remains from Dinosaur National Monument assigned to Allosaurus or Creosaurus (a synonym of Allosaurus), and was to be described by paleontologist Robert Bakker as "Madsenius trux".Lambert, D. (1990) The Dinosaur Data Book, Facts on File, Oxford, England: 320 pp. However, "Madsenius" is now seen as yet another synonym of Allosaurus because Bakker's action was predicated upon the false assumption of USNM 4734 being distinct from long-snouted Allosaurus due to errors in Gilmore's 1920 reconstruction of USNM 4734.
"Wyomingraptor" was informally coined by Bakker for allosaurid remains from the Morrison Formation of the Late Jurassic. The remains unearthed are labeled as Allosaurus and are housed in the Tate Geological Museum. However, there has been no official description of the remains and "Wyomingraptor" has been dismissed as a nomen nudum, with the remains referable to Allosaurus.Bakker, 1997. Raptor family values: Allosaur parents brought great carcasses into their lair to feed their young. In Wolberg, Sump and Rosenberg (eds). Dinofest International, Proceedings of a Symposium, Academy of Natural Sciences. 51–63. |
Allosaurus | Formerly assigned species and fossils | Formerly assigned species and fossils
thumb|left|Antrodemus valens holotype tail vertebra (above) compared to the same of Allosaurus (below)
Several species initially classified within or referred to Allosaurus do not belong within the genus. A. medius was named by Marsh in 1888 for various specimens from the Early Cretaceous Arundel Formation of Maryland, although most of the remains were removed by Richard Swann Lull to the new ornithopod species Dryosaurus grandis, except for a tooth. It was transferred to Antrodemus by Oliver Hay in 1902, but Hay later clarified that this was an inexplicable error on his part. Gilmore considered the tooth nondiagnostic but transferred it to Dryptosaurus, as D. medius. The referral was not accepted in the most recent review of basal tetanurans, and Allosaurus medius was simply listed as a dubious species of theropod. It may be closely related to Acrocanthosaurus.
Allosaurus valens is a new combination for Antrodemus valens used by Friedrich von Huene in 1932; Antrodemus valens itself may also pertain to Allosaurus fragilis, as Gilmore suggested in 1920.
A. lucaris, another Marsh name, was given to a partial skeleton in 1878. He later decided it warranted its own genus, Labrosaurus, but this has not been accepted, and A. lucaris is also regarded as another specimen of A. fragilis. Allosaurus lucaris, is known mostly from vertebrae, sharing characters with Allosaurus. Paul and Carpenter stated that the type specimen of this species, YPM 1931, was from a younger age than Allosaurus, and might represent a different genus. However, they found that the specimen was undiagnostic, and thus A. lucaris was a nomen dubium.
Allosaurus sibiricus was described in 1914 by A. N. Riabinin on the basis of a bone, later identified as a partial fourth metatarsal, from the Early Cretaceous of Buryatia, Russia. It was transferred to Chilantaisaurus in 1990, but is now considered a nomen dubium indeterminate beyond Theropoda.
Allosaurus meriani was a new combination by George Olshevsky for Megalosaurus meriani Greppin, 1870, based on a tooth from the Late Jurassic of Switzerland.Olshevsky, 1978. The archosaurian taxa (excluding the Crocodylia). Mesozoic Meanderings. 1, 1–50. However, a recent overview of Ceratosaurus included it in Ceratosaurus sp.
Apatodon mirus, based on a scrap of vertebra Marsh first thought to be a mammalian jaw, has been listed as a synonym of Allosaurus fragilis.Olshevsky, G., 1991, A revision of the parainfraclass Archosauria Cope, 1869, excluding the advanced Crocodylia. Mesozoic Meanderings 2, 196 pp However, it was considered indeterminate beyond Dinosauria by Chure, and Mickey Mortimer believes that the synonymy of Apatodon with Allosaurus was due to correspondence to Ralph Molnar by John McIntosh, whereby the latter reportedly found a paper saying that Othniel Charles Marsh admitted that the Apatodon holotype was actually an allosaurid dorsal vertebra.
thumb|upright|Mounted skeletons showing Saurophaganax as an Allosaurus-like taxon attacking Apatosaurus sp., in Oklahoma Museum of Natural History. The latter dinosaur may be closer to the actual identity of Saurophaganax, and the former instead represents A. anax
A. amplexus was named by Gregory S. Paul for giant Morrison allosaur remains, and included in his conception Saurophagus maximus (later Saurophaganax). A. amplexus was originally coined by Cope in 1878 as the type species of his new genus Epanterias, and is based on what is now AMNH 5767, parts of three vertebrae, a coracoid, and a metatarsal. Following Paul's work, this species has been accepted as a synonym of A. fragilis. A 2010 neotype designation by Greogry S. Paul and Kenneth Carpenter, however, suggested that Epanterias holotype is temporally younger than the A. fragilis type specimen, and that it is not the same taxon as the Allosaurus holotype.
A. maximus was a new combination by David K. Smith for Chure's Saurophaganax maximus, a taxon created by Chure in 1995 for giant allosaurid remains from the Morrison of Oklahoma. These remains had been known as Saurophagus, but that name was already in use, leading Chure to propose a substitute. Smith, in his 1998 analysis of variation, concluded that S. maximus was not different enough from Allosaurus to be a separate genus, but did warrant its own species, A. maximus. This reassignment was rejected in a review of basal tetanurans. A 2024 reassessment of fossil material assigned to Saurophaganax suggested that the holotype neural arch of this taxon could not confidently be assigned to a theropod, but that it exhibited some similarities to sauropods. Other Saurophaganax bones could be referred to diplodocid sauropods. As such, the researchers assigned the remaining theropod bones to a new species of Allosaurus, A. anax.
There are also several species left over from the synonymizations of Creosaurus and Labrosaurus with Allosaurus. Creosaurus potens was named by Lull in 1911 for a vertebra from the Early Cretaceous of Maryland. It is now regarded as a dubious theropod. Labrosaurus stechowi, described in 1920 by Janensch based on isolated Ceratosaurus-like teeth from the Tendaguru beds of Tanzania, was listed by Donald F. Glut as a species of Allosaurus, is now considered a dubious ceratosaurian related to Ceratosaurus.Tykoski, Ronald S.; and Rowe, Timothy. (2004). "Ceratosauria", in The Dinosauria (2nd). 47–70. L. sulcatus, named by Marsh in 1896 for a Morrison theropod tooth, which like L. stechowi is now regarded as a dubious Ceratosaurus-like ceratosaur.
thumb|left|A. tendagurensis tibia, Naturkunde Museum Berlin
A. tendagurensis was named in 1925 by Werner Janensch for a partial shin (MB.R.3620) found in the Kimmeridgian-age Tendaguru Formation in Mtwara, Tanzania. Although tabulated as a tentatively valid species of Allosaurus in the second edition of the Dinosauria, subsequent studies place it as indeterminate beyond Tetanurae, either a carcharodontosaurian or megalosaurid. Although obscure, it was a large theropod, possibly around long and in weight.
Kurzanov and colleagues in 2003 designated six teeth from Siberia as Allosaurus sp. (meaning the authors found the specimens to be most like those of Allosaurus, but did not or could not assign a species to them). They were reclassified as an indeterminate theropod. Also, reports of Allosaurus in Shanxi, China go back to at least 1982. These were interpreted as Torvosaurus remains in 2012.
An astragalus (ankle bone) thought to belong to a species of Allosaurus was found at Cape Paterson, Victoria in Early Cretaceous beds in southeastern Australia. It was thought to provide evidence that Australia was a refugium for animals that had gone extinct elsewhere. This identification was challenged by Samuel Welles, who thought it more resembled that of an ornithomimid, but the original authors defended their identification. With fifteen years of new specimens and research to look at, Daniel Chure reexamined the bone and found that it was not Allosaurus, but could represent an allosauroid. Similarly, Yoichi Azuma and Phil Currie, in their description of Fukuiraptor, noted that the bone closely resembled that of their new genus. This specimen is sometimes referred to as "Allosaurus robustus", an informal museum name. It likely belonged to something similar to Australovenator, although one study considered it to belong to an abelisaur. |
Allosaurus | Description | Description
thumb|left|The size range of Allosaurus compared with a human
Allosaurus was a typical large theropod, having a massive skull on a short neck, a long, slightly sloping tail, and reduced forelimbs. Allosaurus fragilis, the best-known species, had an average length of and mass of , with the largest definitive Allosaurus specimen (AMNH 680) estimated at long, with an estimated weight of . In his 1976 monograph on Allosaurus, James H. Madsen mentioned a range of bone sizes which he interpreted to show a maximum length of . As with dinosaurs in general, weight estimates are debatable, and since 1980 have ranged between , , and approximately for modal adult weight (not maximum). John Foster, a specialist on the Morrison Formation, suggests that is reasonable for large adults of A. fragilis, but that is a closer estimate for individuals represented by the average-sized thigh bones he has measured. Using the subadult specimen nicknamed "Big Al", since assigned to the species Allosaurus jimmadseni, researchers using computer modeling arrived at a best estimate of for the individual, but by varying parameters they found a range from approximately to approximately . A separate computational project estimated the adaptive optimum body mass in Allosaurus to be ~2,345 kg. A. europaeus has been measured up to in length and in body mass.
thumb|A. jimmadseni skeletal reconstruction
Several gigantic specimens have been attributed to Allosaurus, but may in fact belong to other genera. The dubious genus Saurophaganax (OMNH 1708) was estimated to reach around in length, and its single species was sometimes included in the genus Allosaurus as Allosaurus maximus. However, a 2024 study concluded that some material assigned to Saurophaganax actually belonged to a diplodocid sauropod with the material confidently assigned to Allosauridae belonging to a new species of Allosaurus, A. anax, and the body mass of this species was tentatively estimated around based on fragmentary material. Another potential specimen of Allosaurus, once assigned to the genus Epanterias (AMNH 5767), may have measured in length. A more recent discovery is a partial skeleton from the Peterson Quarry in Morrison rocks of New Mexico; this large allosaurid was suggested to be a potential specimen of Saurophaganax prior to this taxon's 2024 reassessment.Foster, John. 2007. Jurassic West: the Dinosaurs of the Morrison Formation and Their World. Bloomington, Indiana:Indiana University Press. p. 117.
David K. Smith, examining Allosaurus fossils by quarry, found that the Cleveland-Lloyd Dinosaur Quarry (Utah) specimens are generally smaller than those from Como Bluff (Wyoming) or Brigham Young University's Dry Mesa Quarry (Colorado), but the shapes of the bones themselves did not vary between the sites. A later study by Smith incorporating Garden Park (Colorado) and Dinosaur National Monument (Utah) specimens found no justification for multiple species based on skeletal variation; skull variation was most common and was gradational, suggesting individual variation was responsible. Further work on size-related variation again found no consistent differences, although the Dry Mesa material tended to clump together on the basis of the astragalus, an ankle bone. Kenneth Carpenter, using skull elements from the Cleveland-Lloyd site, found wide variation between individuals, calling into question previous species-level distinctions based on such features as the shape of the horns, and the proposed differentiation of A. jimmadseni based on the shape of the jugal. A study published by Motani et al., in 2020 suggests that Allosaurus was also sexually dimorphic in the width of the femur's head against its length. |
Allosaurus | Skull | Skull
thumb|A. jimmadseni skull with diagram highlighting individual bones
The skull and teeth of Allosaurus were modestly proportioned for a theropod of its size. Paleontologist Gregory S. Paul gives a length of for a skull belonging to an individual he estimates at long. Each premaxilla (the bones that formed the tip of the snout) held five teeth with D-shaped cross-sections, and each maxilla (the main tooth-bearing bones in the upper jaw) had between 14 and 17 teeth; the number of teeth does not exactly correspond to the size of the bone. Each dentary (the tooth-bearing bone of the lower jaw) had between 14 and 17 teeth, with an average count of 16. The teeth became shorter, narrower, and more curved toward the back of the skull. All of the teeth had saw-like edges. They were shed easily, and were replaced continually, making them common fossils. Its skull was light, robust and equipped with dozens of sharp, serrated teeth.
The skull had a pair of horns above and in front of the eyes. These horns were composed of extensions of the lacrimal bones, and varied in shape and size. There were also lower paired ridges running along the top edges of the nasal bones that led into the horns. The horns were probably covered in a keratin sheath and may have had a variety of functions, including acting as sunshades for the eyes, being used for display, and being used in combat against other members of the same species (although they were fragile). There was a ridge along the back of the skull roof for muscle attachment, as is also seen in tyrannosaurids.
Inside the lacrimal bones were depressions that may have held glands, such as salt glands. Within the maxillae were sinuses that were better developed than those of more basal theropods such as Ceratosaurus and Marshosaurus; they may have been related to the sense of smell, perhaps holding something like Jacobson's organs. The roof of the braincase was thin, perhaps to improve thermoregulation for the brain. The skull and lower jaws had joints that permitted motion within these units. In the lower jaws, the bones of the front and back halves loosely articulated, permitting the jaws to bow outward and increasing the animal's gape.Paul, Gregory S. (1988). Predatory Dinosaurs of the World. 91 and Figure 4–5 (93). The braincase and frontals may also have had a joint. |
Allosaurus | Postcranial skeleton | Postcranial skeleton
thumb|left|Life restoration of A. fragilis
Allosaurus had nine vertebrae in the neck, 14 in the back, and five in the sacrum supporting the hips.Madsen, 1976; note that not everyone agrees on where the neck ends and the back begins, and some authors such as Gregory S. Paul interpret the count as 10 neck and 13 back vertebrae. The number of tail vertebrae is unknown and varied with individual size; James Madsen estimated about 50, while Gregory S. Paul considered that to be too many and suggested 45 or less. There were hollow spaces in the neck and anterior back vertebrae. Such spaces, which are also found in modern theropods (that is, the birds), are interpreted as having held air sacs used in respiration. The rib cage was broad, giving it a barrel chest, especially in comparison to less derived theropods like Ceratosaurus.Paul, Gregory S. (1988). Predatory Dinosaurs of the World. 277. Allosaurus had gastralia (belly ribs), but these are not common findings, and they may have ossified poorly. In one published case, the gastralia show evidence of injury during life. A furcula (wishbone) was also present, but has only been recognized since 1996; in some cases furculae were confused with gastralia. The ilium, the main hip bone, was massive, and the pubic bone had a prominent foot that may have been used for both muscle attachment and as a prop for resting the body on the ground. Madsen noted that in about half of the individuals from the Cleveland-Lloyd Dinosaur Quarry, independent of size, the pubes had not fused to each other at their foot ends. He suggested that this was a sexual characteristic, with females lacking fused bones to make egg-laying easier. This proposal has not attracted further attention, however.
thumb|Hand and claws of A. fragilis
The forelimbs of Allosaurus were short in comparison to the hindlimbs (only about 35% the length of the hindlimbs in adults) and had three fingers per hand, tipped with large, strongly curved and pointed claws. The arms were powerful, and the forearm was somewhat shorter than the upper arm (1:1.2 ulna/humerus ratio). The wrist had a version of the semilunate carpal also found in more derived theropods like maniraptorans. Of the three fingers, the innermost (or thumb) was the largest, and diverged from the others. The phalangeal formula is 2-3-4-0-0, meaning that the innermost finger (phalange) has two bones, the next has three, and the third finger has four.Martin, A.J. (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. 560 pp. . The legs were not as long or suited for speed as those of tyrannosaurids, and the claws of the toes were less developed and more hoof-like than those of earlier theropods. Each foot had three weight-bearing toes and an inner dewclaw, which Madsen suggested could have been used for grasping in juveniles. There was also what is interpreted as the splint-like remnant of a fifth (outermost) metatarsal, perhaps used as a lever between the Achilles tendon and foot.Paul, Gregory S. (1988). Predatory Dinosaurs of the World. 113; note illustrations of Allosaurus on 310 and 311 as well; Madsen (1976) interpreted these bones as possible upper portions of the inner metatarsal. |
Allosaurus | Skin | Skin
Skin impressions from Allosaurus have been described. One impression, from a juvenile specimen, measures 30 cm² and is associated with the anterior dorsal ribs/pectoral region. The impression shows small scales measuring 1–3 mm in diameter. A skin impression from the "Big Al Two" specimen, associated with the base of the tail, measures 20 cm × 20 cm and shows large scales measuring up to 2 cm in diameter. However, it has been noted that these scales are more similar to those of sauropods, and due to the presence of non-theropod remains associated with the tail of "Big Al Two" there is a possibility that this skin impression is not from Allosaurus.
Another Allosaurus fossil features a skin impression from the mandible, showing scales measuring 1–2 mm in diameter. The same fossil also preserves skin measuring 20 × 20 cm from the ventral side of the neck, showing scutate scales measuring 0.5 cm wide and 11 cm long. A small skin impression from an Allosaurus skull has been reported but never described. |
Allosaurus | Classification | Classification
thumb|right|upright=0.9|Life restoration of A. anax
Allosaurus was an allosaurid, a member of a family of large theropods within the larger group Carnosauria. The family name Allosauridae was created for this genus in 1878 by Othniel Charles Marsh, but the term was largely unused until the 1970s in favor of Megalosauridae, another family of large theropods that eventually became a wastebasket taxon. This, along with the use of Antrodemus for Allosaurus during the same period, is a point that needs to be remembered when searching for information on Allosaurus in publications that predate James Madsen's 1976 monograph. Major publications using the name "Megalosauridae" instead of "Allosauridae" include Gilmore, 1920, von Huene, 1926, Romer, 1956 and 1966, Steel, 1970, and Walker, 1964.
Following the publication of Madsen's influential monograph, Allosauridae became the preferred family assignment, but it too was not strongly defined. Semi-technical works used Allosauridae for a variety of large theropods, usually those that were larger and better-known than megalosaurids. Typical theropods that were thought to be related to Allosaurus included Indosaurus, Piatnitzkysaurus, Piveteausaurus, Yangchuanosaurus, Acrocanthosaurus, Chilantaisaurus, Compsosuchus, Stokesosaurus, and Szechuanosaurus. Given modern knowledge of theropod diversity and the advent of cladistic study of evolutionary relationships, none of these theropods is now recognized as an allosaurid, although several, like Acrocanthosaurus and Yangchuanosaurus, are members of closely related families.
thumb|Illustrations showing the skull of A. jimmadseni from the side (A), top (B), and back (C)
thumb|A. jimmadseni specimen "Big Al II" (SMA 0005)
Below is a cladogram based on the analysis of Benson et al. in 2010.
Allosauridae is one of four families in Allosauroidea; the other three are Neovenatoridae, Carcharodontosauridae and Sinraptoridae. Allosauridae has at times been proposed as ancestral to the Tyrannosauridae (which would make it paraphyletic), one example being Gregory S. Paul's Predatory Dinosaurs of the World,Paul, Gregory S. (1988). "The allosaur-tyrannosaur group", Predatory Dinosaurs of the World. 301–347. but this has been rejected, with tyrannosaurids identified as members of a separate branch of theropods, the Coelurosauria. Allosauridae is the smallest of the carnosaur families, with only Saurophaganax and a currently unnamed French allosauroid accepted as possible valid genera besides Allosaurus in the most recent review. Another genus, Epanterias, is a potential valid member, but it and Saurophaganax may turn out to be large examples of Allosaurus. Some reviews have kept the genus Saurophaganax and included Epanterias with Allosaurus.
The controversial Saurophaganax, initially recognized as a large Allosaurus-like theropod, has had a controversial taxonomic history. In 2019, Rauhut and Pol noted that its taxonomic placement within Allosauroidea is unstable, being recovered as a sister taxon of Metriacanthosauridae or Allosauria, or even as the basalmost carcharodontosaurian. Supplementary information In 2024, Saurophaganax was reassessed as a dubious, chimeric taxon with the holotype being so fragmentary that it could only be confidently referred to the Saurischia, and some specimens more likely belonging to a diplodocid sauropod. |
Allosaurus | Paleobiology | Paleobiology |
Allosaurus | Life history | Life history
thumb|left|Skeletons at different growth stages on display, the Natural History Museum of Utah
The wealth of Allosaurus fossils, from nearly all ages of individuals, allows scientists to study how the animal grew and how long its lifespan may have been. Remains may reach as far back in the lifespan as eggs—crushed eggs from Colorado have been suggested as those of Allosaurus. Based on histological analysis of limb bones, bone deposition appears to stop at around 22 to 28 years, which is comparable to that of other large theropods like Tyrannosaurus. From the same analysis, its maximum growth appears to have been at age 15, with an estimated growth rate of about 150 kilograms (330 lb) per year.
Medullary bone tissue (endosteally derived, ephemeral, mineralization located inside the medulla of the long bones in gravid female birds) has been reported in at least one Allosaurus specimen, a shin bone from the Cleveland-Lloyd Quarry. Today, this bone tissue is only formed in female birds that are laying eggs, as it is used to supply calcium to shells. Its presence in the Allosaurus individual has been used to establish sex and show it had reached reproductive age. However, other studies have called into question some cases of medullary bone in dinosaurs, including this Allosaurus individual. Data from extant birds suggested that the medullary bone in this Allosaurus individual may have been the result of a bone pathology instead. However, with the confirmation of medullary tissue indicating sex in a specimen of Tyrannosaurus, it may be possible to ascertain whether or not the Allosaurus in question was indeed female.
thumb|Restoration of a juvenile Allosaurus
The discovery of a juvenile specimen with a nearly complete hindlimb shows that the legs were relatively longer in juveniles, and the lower segments of the leg (shin and foot) were relatively longer than the thigh. These differences suggest that younger Allosaurus were faster and had different hunting strategies than adults, perhaps chasing small prey as juveniles, then becoming ambush hunters of large prey upon adulthood. The thigh bone became thicker and wider during growth, and the cross-section less circular, as muscle attachments shifted, muscles became shorter, and the growth of the leg slowed. These changes imply that juvenile legs has less predictable stresses compared with adults, which would have moved with more regular forward progression. Conversely, the skull bones appear to have generally grown isometrically, increasing in size without changing in proportion. |
Allosaurus | Feeding | Feeding
thumb|left|Bitten Stegosaurus plate close-up, showing how well the damage matches the front of an Allosaurus "mouth"
Most paleontologists accept Allosaurus as an active predator of large animals. There is dramatic evidence for allosaur attacks on Stegosaurus, including an Allosaurus tail vertebra with a partially healed puncture wound that fits a Stegosaurus tail spike, and a Stegosaurus neck plate with a U-shaped wound that correlates well with an Allosaurus snout. Sauropods seem to be likely candidates as both live prey and as objects of scavenging, based on the presence of scrapings on sauropod bones fitting allosaur teeth well and the presence of shed allosaur teeth with sauropod bones.Fastovsky, David E.; and Smith, Joshua B. (2004). "Dinosaur Paleoecology", in The Dinosauria (2nd ed.). 614–626. However, as Gregory Paul noted in 1988, Allosaurus was probably not a predator of fully grown sauropods, unless it hunted in packs, as it had a modestly sized skull and relatively small teeth, and was greatly outweighed by contemporaneous sauropods. Another possibility is that it preferred to hunt juveniles instead of fully grown adults. Research in the 1990s and the first decade of the 21st century may have found other solutions to this question. Robert T. Bakker, comparing Allosaurus to Cenozoic saber-toothed carnivorous mammals, found similar adaptations, such as a reduction of jaw muscles and increase in neck muscles, and the ability to open the jaws extremely wide. Although Allosaurus did not have saber teeth, Bakker suggested another mode of attack that would have used such neck and jaw adaptations: the short teeth in effect became small serrations on a saw-like cutting edge running the length of the upper jaw, which would have been driven into prey. This type of jaw would permit slashing attacks against much larger prey, with the goal of weakening the victim.
thumb|A. fragilis showing its maximum possible gape, based on Bakker (1998) and Rayfield et al. (2001)
Similar conclusions were drawn by another study using finite element analysis on an Allosaurus skull. According to their biomechanical analysis, the skull was very strong but had a relatively small bite force. By using jaw muscles only, it could produce a bite force of 805 to 8,724 N, but the skull could withstand nearly 55,500 N of vertical force against the tooth row. The authors suggested that Allosaurus used its skull like a machete against prey, attacking open-mouthed, slashing flesh with its teeth, and tearing it away without splintering bones, unlike Tyrannosaurus, which is thought to have been capable of damaging bones. They also suggested that the architecture of the skull could have permitted the use of different strategies against different prey; the skull was light enough to allow attacks on smaller and more agile ornithopods, but strong enough for high-impact ambush attacks against larger prey like stegosaurids and sauropods. Their interpretations were challenged by other researchers, who found no modern analogs to a hatchet attack and considered it more likely that the skull was strong to compensate for its open construction when absorbing the stresses from struggling prey. The original authors noted that Allosaurus itself has no modern equivalent, that the tooth row is well-suited to such an attack, and that articulations in the skull cited by their detractors as problematic actually helped protect the palate and lessen stress. Another possibility for handling large prey is that theropods like Allosaurus were "flesh grazers" which could take bites of flesh out of living sauropods that were sufficient to sustain the predator so it would not have needed to expend the effort to kill the prey outright. This strategy would also potentially have allowed the prey to recover and be fed upon in a similar way later. An additional suggestion notes that ornithopods were the most common available dinosaurian prey, and that Allosaurus may have subdued them by using an attack similar to that of modern big cats: grasping the prey with their forelimbs, and then making multiple bites on the throat to crush the trachea. This is compatible with other evidence that the forelimbs were strong and capable of restraining prey. Studies done by Stephen Lautenschager et al. from the University of Bristol also indicate Allosaurus could open its jaws quite wide and sustain considerable muscle force. When compared with Tyrannosaurus and the therizinosaurid Erlikosaurus in the same study, it was found that Allosaurus had a wider gape than either; the animal was capable of opening its jaws to a 92-degree angle at maximum. The findings also indicate that large carnivorous dinosaurs, like modern carnivores, had wider jaw gapes than herbivores.
left|thumb|Allosaurus and Stegosaurus skeletons, the Denver Museum of Nature and Science
A biomechanical study published in 2013 by Eric Snively and colleagues found that Allosaurus had an unusually low attachment point on the skull for the longissimus capitis superficialis neck muscle compared to other theropods such as Tyrannosaurus. This would have allowed the animal to make rapid and forceful vertical movements with the skull. The authors found that vertical strikes as proposed by Bakker and Rayfield are consistent with the animal's capabilities. They also found that the animal probably processed carcasses by vertical movements in a similar manner to falcons, such as kestrels: The animal could have gripped prey with the skull and feet, then pulled back and up to remove flesh. This differs from the prey-handling envisioned for tyrannosaurids, which probably tore flesh with lateral shakes of the skull, similar to crocodilians. In addition, Allosaurus was able to "move its head and neck around relatively rapidly and with considerable control", at the cost of power.
Other aspects of feeding include the eyes, arms, and legs. The shape of the skull of Allosaurus limited potential binocular vision to 20° of width, slightly less than that of modern crocodilians. As with crocodilians, this may have been enough to judge prey distance and time attacks. The arms, compared with those of other theropods, were suited for both grasping prey at a distance or clutching it close, and the articulation of the claws suggests that they could have been used to hook things. Finally, the top speed of Allosaurus has been estimated at per hour.
A paper on the cranio-dental morphology of Allosaurus and how it worked has deemed the hatchet jaw attack unlikely, reinterpreting the unusually wide gape as an adaptation to allow Allosaurus to deliver a muscle-driven bite to large prey, with the weaker jaw muscles being a trade-off to allow for the widened gape.
thumb|right|Restoration of Barosaurus rearing to defend itself against a pair of A. fragilis
Sauropod carrion may also have been important to large theropods in the Morrison Formation. Forensic techniques indicate that sauropod carcasses were targeted by Allosaurus at all stages of decomposition, indicating that late-stage decay pathogens were not a significant deterrent. A survey of sauropod bones from the Morrison Formation also reported widespread bite marks on sauropod bones in low-economy regions, which suggests that large theropods scavenged large sauropods when available, with the scarcity of such bite marks on the remains of smaller bones being potentially attributable to much more complete consumption of smaller or adolescent sauropods and on ornithischians, which would have been more commonly taken as live prey. A single dead adult Barosaurus or Brachiosaurus would have had enough calories to sustain multiple large theropods for weeks or months, though the vast majority of the Morrison's sauropod fossil record consisted of much smaller-bodied taxa such as Camarasaurus lentus or Diplodocus.
It has also been argued that disabled individuals such as Big Al and Big Al II were physically incapable of hunting due to their numerous injuries but were able to survive nonetheless as scavengers of giant sauropod-falls, Interestingly, a recent review of paleopathologies in theropods may support this conclusion. The researchers found a positive association between allosaurids and fractures to the appendicular skeleton, while tyrannosaurs had a statistically negative association with these types of injuries. The fact that allosaurs were more likely to survive and heal even when severe fractures limited their locomotion abilities can be explained, in part, by different resource accessibility paradigms for the two groups, as allosauroids generally lived in sauropod-inhabited ecosystems, some of which, including the Morrison, have been interpreted as arid and highly water-stressed environments; however, the water-stressed nature of the Morrison has been heavily criticized in several more recent works on the basis of fossil evidence for the presence of extensive forest cover and aquatic ecosystems. |
Allosaurus | Social behavior | Social behavior
thumb|left|The holotype dentary of Labrosaurus ferox, which may have been injured by the bite of another A. fragilis
It has been speculated since the 1970s that Allosaurus preyed on sauropods and other large dinosaurs by hunting in groups.
Such a depiction is common in semitechnical and popular dinosaur literature. Robert T. Bakker has extended social behavior to parental care, and has interpreted shed allosaur teeth and chewed bones of large prey animals as evidence that adult allosaurs brought food to lairs for their young to eat until they were grown, and prevented other carnivores from scavenging on the food. However, there is actually little evidence of gregarious behavior in theropods, and social interactions with members of the same species would have included antagonistic encounters, as shown by injuries to gastralia and bite wounds to skulls (the pathologic lower jaw named Labrosaurus ferox is one such possible example). Such head-biting may have been a way to establish dominance in a pack or to settle territorial disputes.
Although Allosaurus may have hunted in packs, it has been argued that Allosaurus and other theropods had largely aggressive interactions instead of cooperative interactions with other members of their own species. The study in question noted that cooperative hunting of prey much larger than an individual predator, as is commonly inferred for theropod dinosaurs, is rare among vertebrates in general, and modern diapsid carnivores (including lizards, crocodiles, and birds) rarely cooperate to hunt in such a way. Instead, they are typically territorial and will kill and cannibalize intruders of the same species, and will also do the same to smaller individuals that attempt to eat before they do when aggregated at feeding sites. According to this interpretation, the accumulation of remains of multiple Allosaurus individuals at the same site; e.g., in the Cleveland–Lloyd Quarry, are not due to pack hunting, but to the fact that Allosaurus individuals were drawn together to feed on other disabled or dead allosaurs, and were sometimes killed in the process. This could explain the high proportion of juvenile and subadult allosaurs present, as juveniles and subadults are disproportionally killed at modern group feeding sites of animals like crocodiles and Komodo dragons. The same interpretation applies to Bakker's lair sites. There is some evidence for cannibalism in Allosaurus, including Allosaurus shed teeth found among rib fragments, possible tooth marks on a shoulder blade, and cannibalized allosaur skeletons among the bones at Bakker's lair sites. On the other hand, pathological analysis done by Foth et al. argued evidence of surviving serious injuries may support gregariousness in Allosaurus. |
Allosaurus | Brain and senses | Brain and senses
thumb|right|Endocast (cast of the brain cavity) of Allosaurus
The brain of Allosaurus, as interpreted from spiral CT scanning of an endocast, was more consistent with crocodilian brains than those of the other living archosaurs, birds. The structure of the vestibular apparatus indicates that the skull was held nearly horizontal, as opposed to strongly tipped up or down. The structure of the inner ear was like that of a crocodilian, indicating that Allosaurus was more adapted to hear lower frequencies and would have had difficulty hearing subtle sounds. The olfactory bulbs were large and well suited for detecting odors, but were typical for an animal of its size. |
Allosaurus | Paleopathology | Paleopathology
thumb|Mounted A. fragilis skeleton (USNM 4734), which has several healed injuries
In 2001, Bruce Rothschild and others published a study examining evidence for stress fractures and tendon avulsions in theropod dinosaurs and the implications for their behavior. Since stress fractures are caused by repeated trauma rather than singular events they are more likely to be caused by the behavior of the animal than other kinds of injury. Stress fractures and tendon avulsions occurring in the forelimb have special behavioral significance since while injuries to the feet could be caused by running or migration, resistant prey items are the most probable source of injuries to the hand. Allosaurus was one of only two theropods examined in the study to exhibit a tendon avulsion, and in both cases the avulsion occurred on the forelimb. When the researchers looked for stress fractures, they found that Allosaurus had a significantly greater number of stress fractures than Albertosaurus, Ornithomimus or Archaeornithomimus. Of the 47 hand bones the researchers studied, three were found to contain stress fractures. Of the feet, 281 bones were studied and 17 were found to have stress fractures. The stress fractures in the foot bones "were distributed to the proximal phalanges" and occurred across all three weight-bearing toes in "statistically indistinguishable" numbers. Since the lower end of the third metatarsal would have contacted the ground first while an allosaur was running, it would have borne the most stress. If the allosaurs' stress fractures were caused by damage accumulating while walking or running this bone should have experience more stress fractures than the others. The lack of such a bias in the examined Allosaurus fossils indicates an origin for the stress fractures from a source other than running. The authors conclude that these fractures occurred during interaction with prey, like an allosaur trying to hold struggling prey with its feet. The abundance of stress fractures and avulsion injuries in Allosaurus provide evidence for "very active" predation-based rather than scavenging diets.Rothschild, B., Tanke, D. H., and Ford, T. L., 2001, Theropod stress fractures and tendon avulsions as a clue to activity: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 331–336.
The left scapula and fibula of an Allosaurus fragilis specimen cataloged as USNM 4734 are both pathological, both probably due to healed fractures. The specimen USNM 8367 preserved several pathological gastralia which preserve evidence of healed fractures near their middle. Some of the fractures were poorly healed and "formed pseudoarthroses". A specimen with a fractured rib was recovered from the Cleveland-Lloyd Quarry. Another specimen had fractured ribs and fused vertebrae near the end of the tail. An apparent subadult male Allosaurus fragilis was reported to have extensive pathologies, with a total of fourteen separate injuries. The specimen MOR 693 had pathologies on five ribs, the sixth neck vertebra, the third, eighth, and thirteenth back vertebrae, the second tail vertebra and its chevron, the gastralia right scapula, manual phalanx I left ilium metatarsals III and V, the first phalanx of the third toe and the third phalanx of the second. The ilium had "a large hole...caused by a blow from above". The near end of the first phalanx of the third toe was afflicted by an involucrum.
Additionally, a subadult Allosaurus individual that suffered from spondyloarthropathy has been discovered in Dana Quarry in Wyoming. This finding represents the first known fossil evidence of spondyloarthropathy occurring in a theropod.
thumb|Skeletal restoration of "Big Al II" showing bones with pathologies
Other pathologies reported in Allosaurus include:
Willow breaks in two ribs
Healed fractures in the humerus and radius
Distortion of joint surfaces in the foot, possibly due to osteoarthritis or developmental issues
Osteopetrosis along the endosteal surface of a tibia.
Distortions of the joint surfaces of the tail vertebrae, possibly due to osteoarthritis or developmental issues
"[E]xtensive 'neoplastic' ankylosis of caudals", possibly due to physical trauma, as well as the fusion of chevrons to centra
Coossification of vertebral centra near the end of the tail
Amputation of a chevron and foot bone, both possibly a result of bites
"[E]xtensive exostoses" in the first phalanx of the third toe
Lesions similar to those caused by osteomyelitis in two scapulae
Bone spurs in a premaxilla, ungual, and two metacarpals
Exostosis in a pedal phalanx possibly attributable to an infectious disease
A metacarpal with a round depressed fracture |
Allosaurus | Paleoecology | Paleoecology
thumb|left|Locations in the Morrison Formation (yellow) where Allosaurus remains have been found
Allosaurus was the most common large theropod in the vast tract of Western American fossil-bearing rock known as the Morrison Formation, accounting for 70 to 75% of theropod specimens, and as such was at the top trophic level of the Morrison food chain. The Morrison Formation is interpreted as a semiarid environment with distinct wet and dry seasons, and flat floodplains. Vegetation varied from river-lining forests of conifers, tree ferns, and ferns (gallery forests), to fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum.
The Morrison Formation has been a rich fossil hunting ground. The flora of the period has been revealed by fossils of green algae, fungi, mosses, horsetails, ferns, cycads, ginkgoes, and several families of conifers. Animal fossils discovered include bivalves, snails, ray-finned fishes, frogs, salamanders, turtles, sphenodonts, lizards, terrestrial and aquatic crocodylomorphs, several species of pterosaur, numerous dinosaur species, and early mammals such as docodonts, multituberculates, symmetrodonts, and triconodonts. Dinosaurs known from the Morrison include the theropods Ceratosaurus, Ornitholestes, Tanycolagreus, and Torvosaurus, the sauropods Haplocanthosaurus, Camarasaurus, Cathetosaurus, Brachiosaurus, Suuwassea, Apatosaurus, Brontosaurus, Barosaurus, Diplodocus, Supersaurus, Amphicoelias, and Maraapunisaurus, and the ornithischians Camptosaurus, Dryosaurus, and Stegosaurus. Allosaurus is commonly found at the same sites as Apatosaurus, Camarasaurus, Diplodocus, and Stegosaurus. The Late Jurassic formations of Portugal where Allosaurus is present are interpreted as having been similar to the Morrison, but with a stronger marine influence. Many of the dinosaurs of the Morrison Formation are the same genera as those seen in Portuguese rocks (mainly Allosaurus, Ceratosaurus, Torvosaurus, and Stegosaurus), or have a close counterpart (Brachiosaurus and Lusotitan, Camptosaurus and Draconyx).
thumb|alt=Allosaurus and Ceratosaurus fighting|Dry season at the Mygatt-Moore Quarry showing Ceratosaurus (center) and Allosaurus fighting over the desiccated carcass of another theropod
Allosaurus coexisted with fellow large theropods Ceratosaurus and Torvosaurus in both the United States and Portugal. The three appear to have had different ecological niches, based on anatomy and the location of fossils. Ceratosaurus and Torvosaurus may have preferred to be active around waterways, and had lower, thinner bodies that would have given them an advantage in forest and underbrush terrains, whereas Allosaurus was more compact, with longer legs, faster but less maneuverable, and seems to have preferred dry floodplains. Ceratosaurus, better known than Torvosaurus, differed noticeably from Allosaurus in functional anatomy by having a taller, narrower skull with large, broad teeth. Allosaurus was itself a potential food item to other carnivores, as illustrated by an Allosaurus pubic foot marked by the teeth of another theropod, probably Ceratosaurus or Torvosaurus. The location of the bone in the body (along the bottom margin of the torso and partially shielded by the legs), and the fact that it was among the most massive in the skeleton, indicates that the Allosaurus was being scavenged.
A bone assemblage in the Upper Jurassic Mygatt-Moore Quarry preserves an unusually high occurrence of theropod bite marks, most of which can be attributed to Allosaurus and Ceratosaurus, while others could have been made by Torvosaurus given the size of the striations. While the position of the bite marks on the herbivorous dinosaurs is consistent with predation or early access to remains, bite marks found on Allosaurus material suggest scavenging, either from the other theropods or from another Allosaurus. The unusually high concentration of theropod bite marks compared to other assemblages could be explained either by a more complete utilization of resources during a dry season by theropods, or by a collecting bias in other localities. |
Allosaurus | References | References |
Allosaurus | External links | External links
Specimens, discussion, and references pertaining to Allosaurus fragilis at The Theropod Database
Utah State Fossil, Allosaurus (), from Pioneer: Utah's Online Library
Restoration of MOR 693 ("Big Al") and muscle and organ restoration at Scott Hartman's Skeletal Drawing website
List of the many possible Allosaurus species... ()
Category:Allosauridae
Category:Dinosaur genera
Category:Kimmeridgian dinosaurs
Category:Tithonian dinosaurs
Category:Lourinhã Formation
Category:Morrison Formation
Category:Dinosaurs of the United States
Category:Fossil taxa described in 1877
Category:Taxa named by Othniel Charles Marsh |
Allosaurus | Table of Content | mergefrom, Discovery and history, Early discoveries and research, Cleveland-Lloyd discoveries, Modern study, "Big Al" and "Big Al II", Portuguese discoveries, Species, Synonyms, Formerly assigned species and fossils, Description, Skull, Postcranial skeleton, Skin, Classification, Paleobiology, Life history, Feeding, Social behavior, Brain and senses, Paleopathology, Paleoecology, References, External links |
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