Paleobiota of the Niobrara Formation
Introduction ''Pachyrhizodus caninus'' skeletons (casts)Pseudoperna congesta fossil oysters encrusting a large Platyceramus platinus  bivalve shell, Smoky Hill Chalk member of Niobrara Formation . Photo in place at Castle Rock chalk badlands, Kansas.During the time of the deposition of the Niobrara Chalk, much life inhabited the seas of the Western Interior Seaway. By this time in the Late Cretaceous many new lifeforms appeared such as mosasaurs, which were to be some of the last of the aquatic lifeforms to evolve before the end of the Mesozoic. Life of the Niobrara Chalk is comparable to that of the Dakota Formation, although the Dakota Formation, which was deposited during the Cenomanian, predates the chalk by about 10 million years.
Table key
Bony fish ===Pycnodontiformes=== Genus Species Member Abundance Notes ''Micropycnodon'' ''M. kansasensis'' Smoky Hill Chalk A pycnodontiform fish similar but unrelated to modern parrotfish===Semionotiformes=== Genus Species Member Abundance Notes ''Hadrodus'' ''H. marshi'' Smoky Hill Chalk Family Hadrodontidae Thurmond and Jones 1981===Pachycormiformes=== Genus Species Member Abundance Notes Images ''Protosphyraena''  A swordfish-like pachycormid Protosphyraena perniciosa''Bonnerichthys gladius'' ''P. nitida''   ''P. perniciosa'' Smoky Hill Chalk  ''P. tenuis'' Smoky Hill Chalk  ''P. gladius'' Smoky Hill Chalk Named as a new genus, Bonnerichthys ''Bonnerichthys'' ''B. gladius'' Smoky Hill Chalk A filter feeding pachycormid===Crossognathiformes=== Genus Species Member Abundance Notes Images ''Apsopelix'' ''A. anglicus'' Smoky Hill Chalk A crossognathid.Pachyrhizodus sp.'' ''Pachyrhizodus'' ''P. caninus'' Smoky Hill Chalk A pachyrhizodontid ''P. leptopsis'' Smoky Hill Chalk  ''P. minimus'' Smoky Hill Chalk ===Ichthyodectiformes=== Genus Species Member Abundance Notes Images ''Xiphactinus'' ''X. audax'' Smoky Hill Chalk A large ichthyodectid ''Xiphactinus audax''''Ichthyodectes ctenodon''''Gillicus arcuatus''''Saurodon leanus'' ''Ichthyodectes'' ''I. ctenodon'' Smoky Hill Chalk An ichthyodectid ''Gillicus'' ''G. arcuantus'' Smoky Hill Chalk A saurodontid ''Saurodon'' ''S. leanus'' Smoky Hill Chalk A saurodontid ''Saurocephalus'' ''S. lanciformis'' Smoky Hill Chalk A saurodontid===Tselfatiiformes=== Genus Species Member Abundance Notes Images ''Thryptodus'' ''T. zitteli'' Smoky Hill Chalk A plethodid Pentanogmius evolutus'' ''Pentanogmius'' ''P. evolutus'' Smoky Hill Chalk A plethodid ''Martinichthys'' ''M. brevis'' Smoky Hill Chalk A plethodid ''M. xiphoides'' Smoky Hill Chalk  ''Niobrara'' ''N. encarsia'' Smoky Hill Chalk A plethodid ''Zanclites'' ''Z. xenurus'' Smoky Hill Chalk A plethodid===Aulopiformes=== Genus Species Member Abundance Notes Images ''Cimolichthys'' ''C. nepaholica'' Smoky Hill Chalk A cimolichthyid Cimolichthys nepaholica''Enchodus petrosus'' ''Enchodus'' ''E. dirus'' Smoky Hill Chalk An enchodontid ''E. gladiolus'' Smoky Hill Chalk  ''E. petrosus'' Smoky Hill Chalk  ''E. shumardi'' Smoky Hill Chalk  ''Apateodus'' Indeterminate Smoky Hill Chalk An alepisauriform actinopterygiian related to the modern lancetfish and lizardfish ''Stratodus'' ''S. apicalis'' Smoky Hill Chalk An alepisauriform actinopterygiian ''Leptecodon'' ''L. rectus'' An alepisauriform actinopterygiian===Beryciformes=== Genus Species Member Abundance Notes ''Kansius'' ''K. sternbergi'' Smoky Hill Chalk A beryciform actinopterygiian ''Trachichthyoides'' Indeterminate Smoky Hill Chalk A beryciform actinopterygiian ''Caproberyx'' Indeterminate Smoky Hill Chalk A beryciform actinopterygiian===Other bony fish=== Genus Species Member Abundance Notes ''Lepisosteus'' Indeterminate  A lepisosteid gar ''Paraliodesmus'' ''P. guadagnii'' Smoky Hill Chalk An amiiform ''Urenchelys'' ''U. abditus'' Smoky Hill Chalk An anguilliform''Ferrifrons'' ''F. rugosus'' A ferrifronsid acanthomorph''Aethocephalichthys'' ''A. hyainarhinos'' Smoky Hill Chalk An actinopterygian of indeterminate classification''Omosoma'' ''O. garretti'' A polymixiid actinopterygiian closely related to the modern Beardfish''Belonostomus'' Indeterminate An aspidorhynchid
Cartilaginous fish Fish are by far the most common fossils found from the formation, with remains of prehistoric sharks, ray-finned fishes, and lobe-finned fishes in abundance. As well as smaller fish, many large predatory fish were present in the seas at that time, most notably ''Xiphactinus''. Several fish were of close relation to modern day fish including primitive coelacanths, slime heads, lancetfish, gars, swordfish, and salmonids.===Sharks=== Genus Species State Member Abundance Notes Images ''Cretoxyrhina'' ''C. mantelli'' Smoky Hill Chalk A large lamniform shark ''Cretalamna'' ''C. appendiculata'' Smoky Hill Chalk A lamniform shark''Cretalamna appendiculata'' tooth from Israel ''Cretolamna''''C. appendiculata''N/AN/AN/A An extremely widely used ''lapsus calami'' for ''Cretalamna''. ''Johnlongia'' Indeterminate Smoky Hill Chalk An odontaspidid lamniform shark ''Pseudocorax'' ''P. laevis'' Smoky Hill Chalk A lamniform shark smaller than ''Cretoxyrhina'' ''Squalicorax'' ''S. falcatus'' Smoky Hill Chalk A lamniform''Squalicorax falcatus'' tooth from Israel ''S. kaupi'' Smoky Hill Chalk ''Squalicorax kaupi'' tooth from Israel ''S. pristodontus'' Smoky Hill Chalk  ''Scapanorhynchus'' ''S. raphiodon'' Smoky Hill Chalk A mitsukurinid shark similar in appearance to the modern day goblin sharkScapanorhynchus raphiodon'' ''Ptychodus'' ''P. anonymus'' Smoky Hill Chalk A ptychodontid hybodontoid shark ''P. martini'' Smoky Hill Chalk  ''P. mortoni'' Smoky Hill Chalk  ''P. occidentalis'' Smoky Hill Chalk  ''P. polygyrus'' Smoky Hill Chalk ===Other cartilaginous fish=== Genus Species State Member Abundance Notes Images''Edaphodon'' ''E. laqueatus'' A callorhinchid chimaeriform related to the modern ratfish ''Rhinobatos'' fossil ''Rhinobatos'' ''R. incertus'' Smoky Hill Chalk
Dinosaurs An artist's restoration of a dinosaur carcass that has been carried out to sea and some scavenging ''Squalicorax'' sharks. Nonavian dinosaurs have been found in the Niobrara Chalk despite it being located hundreds of miles out to sea at the time. The most reasonable theory is that the carcasses drifted out to sea. It is unlikely that the bodies were carried out by outgoing tides along the shorelines where they died, but rather it is more probable that the dinosaurs were carried offshore by floodwaters during a storm. In the shallow waters the bodies would have begun to decompose and bacteria within the carcass would have produced gasses that would have accumulated in the gut, thereby making the body buoyant. Next, the prevailing winds and currents would have carried it out to sea, where it would eventually settle to the bottom and be buried in sediment.A few caudal vertebrae from a hadrosaur have been found with bite marks and have been eroded, suggesting at one point they were digested. A single tooth belonging to ''Squalicorax'' was found in situ under the vertebrae. This suggested the shark consumed the posterior end of the tail of a floating hadrosaur carcass and had partially digested it before fossilization. Most dinosaurs in the chalk were nodosaurs. The dinosaurs found here were endemic to Appalachia.===Non-avian=== Genus Species State Member Material Notes Images ''Claosaurus'' ''C. agilis'' Kansas "Single articulated postcranial skeleton with associated skull fragments." A small hadrosaurid Claosaurus agilis'' Indeterminate hadrosaurid  A hadrosaurid of indeterminate classification. Possibly ''Corythosaurus.'' ''Niobrarasaurus'' ''N. coleii'' Kansas Smoky Hill Chalk"Partial skeleton." A nodosaurid ankylosaur. ''Hierosaurus''  Kansas Smoky Hill Chalk"Osteoderms." A nodosaurid ankylosaur.===Birds===Three genre of birds are present in the formation, although rare. They were unrelated to modern birds, as they still retained teeth. ''Baptornis'' and ''Hesperornis'' were large flightless aquatic birds suited for diving. ''Ichthyornis'' was a seabird that resembled the gulls and petrels of today. Both probably preyed on small fish and were preyed upon by sharks, large bony fish such as ''Xiphactinus'', and mosasaurs. Genus Species State Member Material Notes Images''Apatornis'' ''A. celer''* Kansas* Nebraska "Postcranial elements." Hesperornis regalis''Ichthyornis dispar'' ''Baptornis'' ''B. advenus'' Smoky Hill Chalk"Fragmentary skull and nearly complete postcranium." A baptornithid hesperornithiform ''Guildavis'' ''G. tener'' Smoky Hill Chalk  ''Hesperornis''  Kansas"Partial postcranial skeleton." ''H. gracilis'' Kansas"Tarsometatarsus." ''H. regalis'' Kansas Smoky Hill Chalk A large hesperornithid hesperornithiform ''Iaceornis'' ''I. marshi'' Smoky Hill Chalk  ''Ichthyornis'' ''I. agilis''  Kansas   Junior synonym of ''I. dispar''. ''I. anceps''  Kansas   Junior synonym of ''I. dispar''. ''I. dispar'' Kansas Smoky Hill Chalk An ichthyornithid ''I. lentus'' Kansas  ''I. tener'' Kansas  ''I. validus''  Kansas   Junior synonym of ''I. dispar''. ''I. victor'' Kansas   Junior synonym of ''I. dispar''. ''Parahesperornis'' ''P. alexi'' Kansas Smoky Hill Chalk"Partial skull and complete postcranium."
Invertebrates Clams, oysters, crinoids, ammonites, and squid are all common in the Niobrara Chalk and must have constituted the majority of life at the time. Evidence of sponges, annelid worms, and crustaceans are less common and are usually found as trace fossils.===Bivalves=== Genus Species Member Abundance Notes Images ''Cladoceramus'' ''C. undulatoplicatus'' Smoky Hill Chalk ''Volviceramus'', ''Durania'', and ''Pseudoperna''. ''Durania'' ''D. maxima'' Smoky Hill Chalk ''Haploscapha''  Fort Hays Limestone ''Inoceramus''  Fort Hays Limestone ''Ostrea''  Fort Hays Limestone ''Platyceramus'' ''P. platinus'' Smoky Hill Chalk ''Pseudoperna'' ''P. congesta'' Smoky Hill Chalk ''Volviceramus'' ''V. grandis'' Smoky Hill Chalk===Cephalopods=== Genus Species Member Abundance Notes Images ''Baculites''  Smoky Hill Chalk ''Baculites'' ''Enchoteuthis'' ''Clioscaphites'' Smoky Hill Chalk ''Rugaptychus''  Smoky Hill Chalk ''Spinaptychus''  Smoky Hill Chalk ''Tusoteuthis'' ''T. longa'' Smoky Hill Chalk  A ''nomen dubium''. ''Enchoteuthis'' ''E. melanae'' Smoky Hill Chalk Most material formerly referred to ''Tusoteuthis'' now belongs to this taxon. ''E. cobbani'' Smoky Hill Chalk ''Niobrarateuthis'' ''N. bonneri'' Smoky Hill Chalk===Echinoderms=== Genus Species State Member Abundance Notes  "Unitacrinus"  "U. socialis"  N/A  N/A  N/A  Common ''lapsus calami'' of ''Uintacrinus'' ''Uintacrinus''
Mosasaurs Tylosaurus proriger'' specimen which was found with a plesiosaur in its stomachMosasaurs are the most common marine reptiles in the Niobrara Chalk and the most successful ones in the sea at the time. Several different genera representing the four different subfamilies of Mosasauridae: the Tylosaurinae, Plioplatecarpinae, Mosasaurinae, and Halisaurinae, were present in Niobrara. They were the dominant carnivorous marine reptiles and ate cephalopods, fish, turtles, pterosaurs, birds, and even plesiosaurs. There is evidence of them consuming other smaller mosasaurs. Despite this, mosasaurs often fell prey to some of the large sharks at the time, such as ''Cretoxyrhina''.The presence of young mosasaurs in the formation suggests that mosasaurs were viviparous and gave birth hundreds of miles out to sea, as Niobrara was in the middle of the Western Interior Seaway at the time. Juveniles would likely have been vulnerable to predation by the many large mid-ocean predators present in the ecosystem. Genus Species Member Abundance Notes Images''Clidastes'' ''C. liodontus'' Smoky Hill Chalk ''C. prophython'' Smoky Hill Chalk''Ectenosaurus'' ''E. clidastoides'' Smoky Hill Chalk ''E. everhartorum'' Smoky Hill Chalk''E. tlemonectes''Smoky Hill Chalk ''Eonatator'' ''E. sternbergii'' Smoky Hill Chalk A small halisaurine ''Platecarpus'' ''P. tympaniticus'' Smoky Hill Chalk A plioplatecarpineTylosaurus nepaeolicus''Anterolateral view of ''Platecarpus tympaniticus'' skull at the Peabody Museum of Natural History.Clidastes propython'' ''Plesioplatecarpus'' ''P. planifrons'' Smoky Hill Chalk''Tylosaurus''''T. nepaeolicus'' Smoky Hill Chalk A large tylosaurine, with the largest ''T. proriger'' reaching about 13 metres in length. ''T. proriger'' Smoky Hill Chalk  ''Selmasaurus'' ''S. johnsoni'' Smoky Hill Chalk
Plesiosaurs Plesiosaurs are present from two different families within Plesiosauroidea in the Niobrara Chalk: the Polycotylidae, or short-necked plesiosaurs, and the Elasmosauridae, or long-necked plesiosaurs. Polycotylids superficially resemble pliosaurs, which are not present within the formation, but are unrelated. They were fast swimmers, unlike the Elasmosaurs that used their long necks to catch fish. Plesiosaurs are rare in the formation and were therefore likely uncommon in the Western Interior Seaway at the time. Specimens become much more numerous in the Pierre Shale situated above the chalk. Genus Species State Member Time span Notes Images ''Polycotylus'' ''P. latipinnis'' Smoky Hill Chalk 84.5-81.5 Ma ago A polycotylid.Styxosaurus snowii''Elasmosaurus platyurus'' ''Dolichorhynchops'' ''D. osborni'' Smoky Hill Chalk 84.5-81.5 Ma ago A polycotylid. also present in the Pierre Shale Formation ''Brimosaurus'' ''B. grandis'' Kansas  A ''nomen dubium''. ''Styxosaurus'' ''S. snowii'' Smoky Hill Chalk 85-81.5 Ma ago A large elasmosaurid, also present in the Pierre Shale Formation''Elasmosaurus'' ''"E." sternbergi'' Smoky Hill Chalk 84.5-81.5 Ma ago Most likely not referable to ''Elasmosaurus''.
Pterosaurs Two genre of pterosaurs are present in the formation, both within Pterodactyloidea: the pteranodontid ''Pteranodon'' (sometimes broken into several genera like ''Geosternbergia'' and ''Dawndraco'', though this is dubious) and the nyctosaurid ''Nyctosaurus''. They are large pterosaurs with elongated cranial crests. The pterosaurs of Niobrara probably spent most of their time at sea and rarely went on land, with ''Nyctosaurus'' being a probably fully pelagic animal. ''Pteranodon'' probably foraged on the ocean surface, while ''Nyctosaurus'' was a frigatebird-like aerial predator. Genus Species Member Time span Notes Images ''Nyctosaurus'' ''N. gracilis'' Smoky Hill Chalk A nyctosaurid ornithocheiroid. Nyctosaurus sp.'' ''Pteranodon''  Smoky Hill Chalk86–84.5 Ma ago  A large and very abundant pteranodontid ornithocheiroid. ''Geosternbergia''  Smoky Hill Chalk86–84.5 Ma ago   A species of Pterosaur that is regarded by a few Paleontologists to be a species of Pteranodon, though most regard it as a distinct species.
Turtles Sea turtles have been found from the Niobrara Chalk that reached large sizes. The biggest, ''Archelon'', was considerably larger than its distant relative, the leatherback sea turtle, which is the largest of the sea turtles alive today. The sea turtles most likely fed on ammonites, squid, and other cephalopods. Genus Species Member Abundance Notes Images ''Bothremys'' ''B. barberi'' Smoky Hill ChalkProtostega gigas'' ''Chelosphargis'' ''C. advena'' Smoky Hill Chalk  ''Ctenochelys'' ''C. stenopora'' Smoky Hill Chalk  ''Porthochelys'' ''P. laticeps'' Smoky Hill Chalk A toxichelid cryptodire ''Protostega'' ''P. gigas'' Smoky Hill Chalk A protostegid cryptodire ''Toxochelys'' ''T. latiremis'' Smoky Hill Chalk A chelonioid cryptodire
Footnotes
References * Everhart, Michael J. ''Oceans Of Kansas: A Natural History Of The Western Interior Sea'' (Life of the Past). Bloomington: Indiana University Press, 2005.322 pp. * Everhart, Michael J. 2006. "The Occurrence of Elasmosaurids (Reptilia: Plesiosauria) in the Niobrara Chalk of Western Kansas"; ''Paludicila''; 5(4) pp. 170–183* Shimada, K. 2007. "Skeletal and dental anatomy of lamniform shark, Cretalamna appendiculata from Upper Cretaceous Niobrara Chalk of Kansas". ''Journal of Vertebrate Paleontology'', 27(3):584–602. * Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds. ): ''The Dinosauria'', 2nd, Berkeley: University of California Press. 861 pp. .