Not so very long ago, the Americas were home to giant mammals: monstrous-sized beavers, ground sloths weighing over 4,000 pounds, the well-known woolly mammoths and saber-tooth cats, and many more.
These megafauna, which is ancient Greek for “large animals,” thrived in the geological period called the Pleistocene epoch, which spans 1.8 million to 12,000 years ago. (For perspective, most of the dinosaurs went extinct around 65 million years ago.) The Pleistocene era ended with the end of the last ice age, along with the sudden extinction of most of the American megafauna.
Although it’s unclear what’s responsible for the mass extinctions, two main factors are suspected: dramatic climate change at the end of the ice age and arrival of humans.
Ancestors of modern Native Americans, the Clovis people, arrived in North America around 12,000 years ago, crossing the Bering Straight. They may have played a part in these extinctions directly, such as through hunting, or indirectly, such as through spreading new diseases and/or disrupting established ecosystems. These factors or others caused the extinction of around 30 genera of megafauna in North America and 45 genera in South America between 10,000 to 12,000 years ago. The megafauna spanned a huge range of sizes and shapes; this article can only highlight a few, but to encounter more of these giants personally, this author recommends a trip to the La Brea Tar Pits in Los Angeles.
Although often depicted as huge wolves in popular culture, the dire wolf (Canis dirus) was actually smaller than some living northern timber wolves, reaching five feet long and weighing around 110 pounds. Making up for their relatively small size, they had massive teeth and hunted in large packs. The dire wolves spread across North and Central America, coexisting with the smaller grey wolves (Canis Lupus), and were predominant hunters in California; remains of thousands have been recovered at the La Brea Tar Pits.
Though today we think of them as a very small group of animals, rodents larger than wolves were common not so long ago. Only one existing species helps remind us what these giants were like: The largest living rodent, the capybara (Hydrochoerus hydrochaeris) looks like a four-foot-long, 140-pound guinea pig. However, unlike guinea pigs, capybaras are semi-aquatic and have webbed feet. Although they’re native to South America, you can catch them swimming at the Santa Barbara Zoo. Until 11,000 years ago, capybaras weighing around 200 to 250 pounds (Neochoerus pinckneyi) roamed the Americas.
Another colossal rodent was the giant beaver (Castoroides ohioensis). Building huge lodges in North America, these beavers reached up to nine feet long. Minus the two-foot-long tail, their bodies were comparable in size to that of a black bear.
Large cats were well-represented Pleistocene megafauna as well. The North American lion (Panthera leo atrox) was a quarter again as big as any existing large Eurasian cat. However, “lion” may be a misnomer; it may be closer to a gigantic jaguar. Spread across the Americas, these cats were common in California; around 100 have been recovered from the La Brea Tar Pits.
Multiple types of saber-tooth cats (subfamily Machairodontinae) hunted in America too. The “scimitar cat” is a smaller, lesser-popularized saber-tooth cat (genus Homotherium, literally “man’s beast”). This cat, about the size of a lion but with a hyena-like build, weighed up to 600 pounds. As their name implies, scimitar cats not only had impressive five-inch-long canines, but those teeth had razor-sharp edges. They once lived throughout Africa, Eurasia, and North America. The more popularized saber-tooth cats of the Americas (genus Smilodon) included three species, all of a compact, muscular build. The largest species (Smilodon populator), at four feet tall and seven feet long, may have weighed over 800 pounds. This mass was topped off with distinctive seven-inch-long canines.
A variety of hoofed animals also roamed ancient America, including several horse species. The extinct Western horse (Equus occidentalis) was similar in size to a modern Arabian horse, but heavier in build, while the smaller, 500-pound Equus conversidens was just one of many petite horse species. Around 11,000 years ago all horses disappeared from the American continents, but were reintroduced by Spanish explorers in the 1500s A.D.
The large, moose-like deer (Cervalces scotti), at an impressive 1,000 pounds, was larger than modern moose. The woodland musk-ox (Bootherium bombifrons), the only ox that evolved and stayed in North America, was even more massive. Large camels (genus Camelops) also once called America home; some were seven feet tall at the shoulder, slightly taller than modern camels, and weighed just over 2,000 pounds.
Claiming the title for the largest mammalian land carnivore of the time was the giant short-faced bear (Arctodus simus). The largest males were probably just over five feet at the shoulders, and eleven and a half feet tall when standing on their hind legs. Weighing an amazing 2,500 pounds, they’re the largest bear ever to exist.
With some members even larger than these amazing bears, over 80 genera of Pleistocene ground sloths existed. Although three-toed and two-toed tree sloths still exist, these are much smaller than their ancient relatives. Giant ground sloths had huge stout claws and great crushing ability. Smaller giant ground sloths, weighing a mere 1,400 pounds, were browsers (family Megatheriidae) and ate leafy material, reaching for high branches on their hind limbs. Grazing ground sloths (family Mylodontidae) preferred open stretches of grassy land. These massive sloths were over six feet tall, and weighed around 4,400 pounds. Another family (Megalonychidae) is famous for being first described by Thomas Jefferson in 1794, as he discovered giant remains in western Virginia caves (the species was consequently named Megalonyx jeffersoni). Some members weighed nearly 3,000 pounds.
Related to the ground sloths, giant armadillos the size of cars once inhabited these lands. Unlike modern insect-eating armadillos, these giants ate plants. Two families of giant armadillos existed, each having tortoise-like armor; bone segments formed a huge shell around their back. Members of one family (Pampatheriidae) were relatively small, weighing 440 pounds, while the largest members of the other family (Glyptodontidae) weighed around 4,400 pounds.
Even larger still, the American mastodon (Mammut americanum) resembled a furry elephant, and is often mistaken for the woolly mammoth. Mastodons browsed cold North American woodlands and weighed an awesome 12,000 pounds. They have a distinct large hole in their skulls, which is their nasal cavity. It’s theorized that discovery of these remains by ancient Greeks and others may have inspired myths about the giant Cyclops.
Largest of all, some legendary Woolly Mammoth (genus Mammuthus) bulls may have weighed 20,000 pounds. For comparison, the current largest land mammal is the African elephant, with bulls usually around 13,000 pounds. The mammoths spread across North America and Eurasia, eating tundra grass. They had meter-thick fur with a thick undercoat the mastodon may not have had, as well as longer, more curved tusks. Ancient cultures often believed their remains to be the bones of giants. Only in the last few centuries have scientists recognized them as a species distinct from Asian elephants, which they are quite similar to. Many specimens have been found nearly intact due to their having left their bodies in frozen areas; enough DNA has been recovered to sequence their genome.
Although we may never know exactly what caused the massive extinction of so many prehistoric behemoths, their existence and unlikely rapid demise reminds us of the importance of present conservation efforts. Today we can only catch a glimpse of what these giants were like, watching some of their lucky little cousins that still scurry across the lands.
For more on Pleistocene megafauna of America, see Chester Stock’s Rancho La Brea: A Record of Pleistocene Life in California, W. David Lambert and Crawford S. Holling’s “Causes of Ecosystem Transformation at the End of the Pleistocene: Evidence from Mammal Body-Mass Distributions,” Gary Haynes’ “American Megafaunal Extinctions at the End of the Pleistocene” Wikipedia’s “Megafauna,” Wikipedia’s “Pleistocene Megafauna,” Wikipedia’s “New World Pleistocene Extinctions.”
Biology Bytes author Teisha Rowland is a science writer, blogger at All Things Stem Cell, and graduate student in molecular, cellular, and developmental biology at UCSB, where she studies stem cells. Send any ideas for future columns to her at email@example.com.
Katika karne ya kwanza, Amerika ilikuwa na mamalia wakubwa kama vile beavers, sloths, na mammoths, na wengine wengi. "Megafauna, neno la Kigiriki la kale linalomaanisha ""wanyama wakubwa,"" ilitokea katika kipindi cha kijiolojia kinachoitwa Pleistocene, ambacho kilianza miaka milioni 1.8 hadi 12,000 iliyopita." Kwa mfano, dinosaurs walipotea miaka milioni 65 hivi iliyopita. Enzi ya Pleistocene ilikoma na mwisho wa enzi ya barafu ya mwisho, pamoja na kutoweka ghafula kwa megafauna nyingi za Amerika. Ingawa haijulikani ni nini kinachosababisha kutoweka kwa jamii nyingi, kuna sababu mbili kuu zinazodhaniwa: mabadiliko makubwa ya hali ya hewa mwishoni mwa enzi ya barafu na kuwasili kwa wanadamu. Wenyeji wa Amerika ya Kaskazini, watu wa Clovis, waliwasili Amerika Kaskazini karibu miaka 12,000 iliyopita, wakivuka Bering Strait. Huenda ikawa walihusika katika kutoweka kwa wanyama hao moja kwa moja, kama vile kwa kuwinda, au kwa njia isiyo ya moja kwa moja, kama vile kwa kueneza magonjwa mapya na kuharibu mazingira yaliyopo. Katika miaka ya hivi karibuni, jamii ya megafauna ya Amerika ya Kaskazini imekufa kwa karibu miaka 10,000 hadi 12,000 iliyopita. Megafauna ilikuwa na ukubwa na maumbo mbalimbali; makala hii inaweza tu kuonyesha chache, lakini kukutana zaidi ya majitu haya binafsi, mwandishi anapendekeza safari ya La Brea Tar Pits katika Los Angeles. Ingawa mara nyingi huonyeshwa kama mbwa mwitu mkubwa katika utamaduni maarufu, mbwa mwitu mbaya (Canis dirus) kwa kweli alikuwa mdogo kuliko mbwa mwitu wa kaskazini wanaoishi, kufikia urefu wa futi tano na uzito wa karibu pauni 110. Ili kulipia ukubwa wao mdogo, walikuwa na meno makubwa na waliwinda katika makundi makubwa. Mbwa-mwitu wa kawaida walienea katika Amerika ya Kaskazini na Kati, wakiishi pamoja na mbwa-mwitu wa kijivu (Canis lupus), na walikuwa wawindaji wakuu huko California; mabaki ya maelfu yamepatikana katika La Brea Tar Pits. Ingawa leo tunawaona kuwa kundi dogo sana la wanyama, wanyama wadudu wakubwa kuliko mbwa-mwitu walikuwa wa kawaida si muda mrefu uliopita. "Kuna aina moja tu ya nyigu inayoweza kutukumbusha jinsi majitu hayo yalivyokuwa: ""Hydrochaerus hydrochaeris"" (kapibara) - nyigu mkubwa zaidi aliye hai - anaonekana kama nguruwe wa Guinea mwenye urefu wa meta moja na uzito wa pauni 140." Hata hivyo, tofauti na nguruwe wa Guinea, capybaras huishi nusu majini na wana miguu yenye utando. Ingawa wao ni wenyeji wa Amerika Kusini, unaweza kuwapata wakigelea katika bustani ya wanyama ya Santa Barbara. Kabla ya miaka 11,000 iliyopita, capybaras wenye uzito wa karibu pauni 200 hadi 250 (Neochoreus pinkeye) walizunguka Amerika. Mdudu mwingine mkubwa alikuwa beaver mkubwa (Castoroides ohioensis). Wakiwa wakijenga vibanda vikubwa huko Amerika Kaskazini, beavers hao walifikia urefu wa meta tisa. Isipokuwa mkia wao wenye urefu wa meta mbili, miili yao ilikuwa na ukubwa unaolingana na ule wa dubu mweusi. Paka wakubwa pia walikuwa sehemu kubwa ya wanyama wakubwa wa Pleistocene. Simba wa Amerika Kaskazini (Panthera leo atrox) alikuwa na ukubwa wa robo ya paka yeyote mkubwa wa Eurasia aliyewahi kuishi. Hata hivyo, huenda neno "simba" likawa lisilofaa; huenda likakaribia zaidi jaguar mkubwa. Wakiwa wametangazwa katika Amerika, paka hao walikuwa wa kawaida huko California; karibu 100 wamepatikana katika mashimo ya lami ya La Brea. Aina nyingi za paka wenye meno ya upanga (familia ndogo ya Machairodontinae) zilivuliwa pia huko Amerika. "Paka wa scimitar" ni paka mdogo, asiyejulikana sana wa meno ya upanga (jinsia ya Homotherium, kihalisi "mnyama wa mwanadamu"). Paka huyo alikuwa na ukubwa wa simba lakini alikuwa na umbo la mnyama anayeitwa hyena, na alikuwa na uzito wa kilo 300. Kama jina lake linavyodokeza, paka hao walikuwa na meno marefu sana, na pia meno yao yalikuwa na ncha kali kama mashine ya kunyoa. Wakati mmoja waliishi kotekote Afrika, Eurasia, na Amerika Kaskazini. Paka wenye meno ya upanga wa Amerika (jamii ya Smilodon) walijulikana zaidi walitia ndani spishi tatu, zote zilikuwa na umbo dogo, lenye misuli. Aina kubwa zaidi (Smilodon populator), yenye urefu wa meta nne na urefu wa mita saba, huenda ilizidi pauni 800. Mkusanyiko huo uliongezwa na meno ya kipekee yenye urefu wa inchi saba. Wanyama mbalimbali wenye manyoya pia walitembea-tembea katika Amerika ya kale, kutia ndani spishi kadhaa za farasi. Farasi wa Magharibi (Equus occidentalis) alikuwa na ukubwa sawa na farasi wa Kiarabu wa kisasa, lakini alikuwa mzito zaidi, wakati farasi mdogo wa Kiarabu (Equus conversidens) alikuwa mmoja tu wa aina nyingi za farasi wadogo. Katika miaka ya 1500 na 1500, farasi walipotea katika Amerika, lakini walianzishwa tena na watafiti wa Kihispania. Nyati aina ya Cervalces scotti, ambayo ni aina ya mwerezi, ilikuwa na uzito wa kilogramu 1,000 na ilikuwa kubwa kuliko mwerezi wa leo. Ng'ombe-dume wa msitu (Bootherium bombifrons), ng'ombe-dume pekee aliyebadilika na kubaki Amerika Kaskazini, alikuwa mkubwa hata zaidi. "Kama vile ngamia wakubwa (kabila la Camelops) walivyoitwa Amerika wakati mmoja; baadhi yao walikuwa na urefu wa futi saba kwenye bega, mrefu kidogo kuliko ngamia wa kisasa, na walipima zaidi ya pauni 2,000.""" Dubu mkubwa mwenye uso mfupi (Arctodus simus) ndiye aliyedai kuwa mnyama mkubwa zaidi wa nchi kavu wa wakati huo. Wanaume wakubwa zaidi walikuwa labda zaidi ya futi tano kwenye mabega, na futi moja na nusu kwa urefu waliposimama juu ya miguu yao ya nyuma. Kwa kuwa wana uzito wa kilo 2,500, wao ndio dubu wakubwa zaidi kuwahi kuishi. Kwa kuwa baadhi ya wanyama hao walikuwa wakubwa kuliko dubu hao, kulikuwa na jamii zaidi ya 80 za wanyama hao. Ingawa viumbe hao wenye vidole vitatu na viwili bado wapo, wao ni wadogo sana kuliko watu wao wa kale. Vipepeo wakubwa wa ardhini walikuwa na makucha makubwa na uwezo mkubwa wa kuvunja. Vipepeo wadogo wa ardhi wenye uzito wa pauni 1,400 tu walikuwa wavuvi (familia ya Megatheriidae) na walikula majani, wakifikia matawi marefu kwenye viungo vyao vya nyuma. Wanyama hao waliopenda malisho (familia ya Mylodontidae) walipenda maeneo ya wazi yenye nyasi. Wanyama hao walikuwa na urefu wa zaidi ya meta mbili na uzito wa karibu pauni 4,400. Megalonychidae ni familia ya wanyama wa aina ya Megalonychidae, ambayo ilitambuliwa na Thomas Jefferson mnamo 1794, wakati alipogundua mabaki makubwa ya wanyama katika mapango ya magharibi mwa Virginia. Baadhi ya washiriki hao walikuwa na uzito wa karibu pauni 3,000! Wenye ukoo na viumbe wa chini ya ardhi, armadillo wakubwa wenye ukubwa wa magari wakati mmoja waliishi katika maeneo hayo. Tofauti na armadillo wa kisasa wanaokula wadudu, majitu hayo yalikula mimea. Kulikuwa na familia mbili za armadillo wakubwa, kila mmoja akiwa na silaha kama za kasa; sehemu za mifupa zilifanyiza ganda kubwa kwenye mgongo wao. Wanyama wa familia moja (Pampatheriidae) walikuwa wadogo sana, wakizidi pauni 440 wakati wale wa familia nyingine (Glyptodontidae) walikuwa wazito wa pauni 4,400 hivi. Mammoth wa Amerika (Mammut americanum) ni aina ya tembo mwenye manyoya mengi, na mara nyingi huonwa kimakosa kuwa mamothi mwenye manyoya mengi. Mastodon alikuwa mnyama wa kawaida katika misitu ya Amerika Kaskazini na alikuwa na uzito wa kilo 12,000 hivi. Wana shimo kubwa katika fuvu lao la kichwa, ambalo ni shimo la pua yao. Inadhaniwa kwamba ugunduzi wa mabaki hayo na Wagiriki wa kale na wengine huenda ulichochea hekaya kuhusu Cyclops mkubwa. Mnyama huyo wa kipekee, Mammoth Woolly, alikuwa na uzito wa kilo 20,000. Kwa kulinganisha, mnyama mkubwa zaidi duniani ni tembo wa Afrika, ambaye kwa kawaida ana uzito wa karibu pauni 13,000. Mamoths hao walienea kotekote Amerika Kaskazini na Eurasia, wakila nyasi za tundra. Mastodon alikuwa na manyoya yenye unene wa mita moja na manyoya mengi ya chini ambayo huenda mastodon hakuwa nayo, na pia alikuwa na meno marefu na yenye umbo la mviringo. Mara nyingi tamaduni za kale ziliamini kwamba mabaki yao yalikuwa mifupa ya majitu. Ni katika karne chache zilizopita tu ambapo wanasayansi wametambua kwamba tembo ni spishi tofauti na tembo wa Asia, ambao wanafanana sana nao. Spishi nyingi zimepatikana karibu zikiwa zimeharibika kwa sababu wameacha miili yao katika maeneo ya barafu; DNA ya kutosha imepatikana ili kuorodhesha genome yao. Ingawa huenda tusijue kamwe hasa ni nini kilichosababisha kutoweka kwa wingi kwa wanyama wengi wa kale, kuwepo kwao na kutoweka kwao kwa haraka kunatukumbusha umuhimu wa jitihada za sasa za kuwalinda. Leo tunaweza tu kupata ufahamu wa jinsi majitu haya yalivyokuwa, tukitazama baadhi ya binamu zao wa bahati ndogo ambao bado wanakimbia katika nchi. "Kama ilivyoelezwa katika makala ya ""Megafauna ya Amerika ya Pleistocene"" na ""Rancho LaBrea: Rekodi ya Maisha ya Pleistocene huko California"" na ""Wikipedia: Sababu za Mabadiliko ya Ecosystem mwishoni mwa Pleistocene: Ushahidi kutoka kwa Usambazaji wa Mwili wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama wa Mnyama.""" 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