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 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. Pycnodontiformes Genus Species MemberAge Abundance Notes Micropycnodon M. kansasensis Smoky Hill ChalkLate Coniacian-Satonian A pycnodontiform fish similar but unrelated to modern parrotfish Hadrodus H. marshi Smoky Hill ChalkEarly Campanian Family Hadrodontidae Thurmond and Jones 1981

Pachycormiformes Genus Species Member AbundanceAge Notes Images Protosphyraena A swordfish-like pachycormid P. nitida Late Coniacian P. perniciosa Smoky Hill Chalk Late Coniacian- Early Campanian? P. tenuis Smoky Hill Chalk Santonian- Early Campanian P. gladius Smoky Hill Chalk Named as a new genus, Bonnerichthys BonnerichthysViegas, Jennifer (18 February 2010), SUV-Sized Fish Were Earliest Filter-Feeders, Discovery News, retrieved 1 April 2010 B. gladius Smoky Hill ChalkLate Coniacian- Early Campanian A filter feeding pachycormid

Crossognathiformes Genus Species MemberAbundance Age Notes Images Apsopelix A. anglicus Smoky Hill ChalkLate Coniacian- Early Campanian A crossognathid. Pachyrhizodus P. caninus Smoky Hill ChalkLate Coniacian- Early Campanian A pachyrhizodontid P. leptopsis Smoky Hill Chalk Late Coniacian- Santonian P. minimus Smoky Hill Chalk Late Coniacian- Early Campanian

Ichthyodectiformes Genus Species MemberAbundance Age Notes Images Xiphactinus X. audax Smoky Hill ChalkLate Coniacian- Early Campanian A large ichthyodectid Ichthyodectes I. ctenodon Smoky Hill ChalkLate Coniacian- Early Campanian An ichthyodectid Gillicus G. arcuatus Smoky Hill ChalkLate Coniacian- Early Campanian A saurodontid Saurodon S. leanus Smoky Hill ChalkLate Coniacian- Santonian A saurodontid Saurocephalus S. lanciformis Smoky Hill ChalkEarly Campanian A saurodontidProsaurodonP. pygmaeusSmoky Hill ChalkSantonian

Tselfatiiformes Genus Species Member AbundanceAge Notes Images Thryptodus T. zitteli Smoky Hill ChalkLate Coniacian A plethodid Pentanogmius P. evolutus Smoky Hill ChalkEarly Campanian A plethodid Martinichthys M. brevis Smoky Hill ChalkLate Coniacian A plethodid M. xiphoides Smoky Hill Chalk Late Coniacian Niobrara N. encarsia Smoky Hill ChalkSantonian A plethodid Zanclites Z. xenurus Smoky Hill ChalkSantonian A plethodid

Aulopiformes Genus Species Member AbundanceAge Notes Images Cimolichthys C. nepaholica Smoky Hill ChalkLate Coniacian- Early Campanian A cimolichthyid Enchodus E. dirus Smoky Hill ChalkLate Coniacian- Santonian An enchodontid E. gladiolus Smoky Hill Chalk Late Coniacian- Early Campanian E. petrosus Smoky Hill Chalk Late Coniacian- Early Campanian E. shumardi Smoky Hill Chalk Late Coniacian- Early Campanian Apateodus A. busseni Smoky Hill ChalkEarly Campanian An alepisauriform actinopterygiian related to the modern lancetfish and lizardfishIndeterminateSantonian Stratodus S. apicalis Smoky Hill ChalkLate Coniacian- Early Campanian An alepisauriform actinopterygiian Leptecodon L. rectusEarly Campanian An alepisauriform actinopterygiian

Beryciformes Genus Species Member AbundanceAge Notes Kansius K. sternbergi Smoky Hill ChalkEarly Campanian A beryciform actinopterygiian Trachichthyoides Indeterminate Smoky Hill ChalkSantonian A beryciform actinopterygiian Caproberyx Indeterminate Smoky Hill ChalkSantonian A beryciform actinopterygiian

Other bony fish Genus Species Member AbundanceAge Notes Lepisosteus Indeterminate Late Coniacian A lepisosteid gar Paraliodesmus"Table 13.1: Bony Fish", Everhart (2005), page 245. P. guadagnii Smoky Hill ChalkLate Coniacian- Santonian An amiiform Urenchelys U. abditus Smoky Hill ChalkSantonian An anguilliformFerrifrons F. rugosus A ferrifronsid acanthomorphAethocephalichthys A. hyainarhinos Smoky Hill ChalkLate Coniacian- Early Campanian An actinopterygian of indeterminate classificationFielitz, C.; Stewart, J. D.; & Wiffen, J. 1999. Aethocephalichthys hyainarhinos gen. et sp. nov., a new and enigmatic Late Cretaceous actinopterygian from North America and New Zealand. Mesozoic Fishes 2 – Systematics and Fossil Record, G. Arratia & H.-P. Schultze (eds.): pp. 95-106, 7 figs.Omosoma O. garretti A polymixiid actinopterygiian closely related to the modern BeardfishBelonostomus"Table 13.1: Bony Fish", Everhart (2005), page 244. Indeterminate An aspidorhynchid

Cartilaginous fish

Sharks Genus Species State Member AbundanceAge Notes Images Cretoxyrhina C. mantelli Smoky Hill ChalkLate Coniacian- Early Campanian A large lamniform shark Cretalamna"Table 13.1: Sharks/Rays," Everhart (2005), page 244. Note that Cretalamna is listed here under the widely used lapsus calami Cretolamna. C. appendiculata Smoky Hill ChalkLate Coniacian- Early Campanian A lamniform shark CretolamnaC. appendiculataN/AN/AN/A An extremely widely used lapsus calami for Cretalamna."Introduction", in "Skeletal and Dental Anatomy..." Shimada (2007), page 584 Johnlongia"Table 13.1: Sharks/Rays", Everhart (2005), page 244 Indeterminate Smoky Hill ChalkLate Coniacian An odontaspidid lamniform shark Pseudocorax P. laevis Smoky Hill ChalkLate Coniacian- Santonian A lamniform shark smaller than Cretoxyrhina Squalicorax S. falcatus Smoky Hill ChalkLate Coniacian- Santonian A lamniform S. kaupi Smoky Hill ChalkSantonian- Early Campanian S. pristodontus Smoky Hill ChalkEarly CampanianS.microserratodonLate Coniacian Scapanorhynchus S. raphiodon Smoky Hill ChalkLate Coniacian A mitsukurinid shark similar in appearance to the modern day goblin shark Ptychodus P. anonymus Smoky Hill Chalk A ptychodontid lamniform shark P. martini Smoky Hill ChalkLate ConiacianP. mortoni Smoky Hill ChalkLate Coniacian- Santonian P. occidentalis Smoky Hill Chalk P. polygyrus Smoky Hill Chalk

Other cartilaginous fish Genus Species State Member AbundanceAge Notes ImagesEdaphodon E. laqueatus A callorhinchid chimaeriform related to the modern ratfish Rhinobatos R. incertus Smoky Hill ChalkLate Coniacian- Early Campanian

Reptiles Dinosaurs 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.Everhart, M. J. and K. Ewell. 2006. Shark-bitten dinosaur (Hadrosauridae) vertebrae from the Niobrara Chalk (Upper Coniacian) of western Kansas. Kansas Academy of Science, Transactions, 109 (1-2):27-35. Most dinosaurs in the chalk were nodosaurs. The dinosaurs found here were endemic to Appalachia.

Non-avian Genus Species State Member MaterialAge Notes Images Claosaurus"Table 13.1: Dinosaurs", Everhart (2005), page 246. C. agilis Kansas "Single articulated postcranial skeleton with associated skull fragments.""Table 20.1," in Weishampel, et al. (2004). Page 439.Early Campanian A small hadrosaurid Indeterminate hadrosaurid Santonian A hadrosaurid of indeterminate classification. Possibly Corythosaurus. Niobrarasaurus N. coleii Kansas Smoky Hill Chalk"Partial skeleton.""Table 17.1," in Weishampel, et al. (2004). Page 367.Late Coniacian- Santonian A nodosaurid ankylosaur. Hierosaurus Kansas Smoky Hill Chalk"Osteoderms.""Table 17.1," in Weishampel, et al. (2004). Page 368.Late Coniacian 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 MaterialAge Notes ImagesApatornis"Table 13.1: Birds," Everhart (2005), page 246. A. celer Kansas Nebraska"Dinosaur distribution (Late Cretaceous; North America; Nebraska; Niobrara Chalk Formation)." Weishampel, et al. (2004). Pp. 586. "Postcranial elements.""Table 11.1," in Weishampel, et al. (2004). Page 214.Early Campanian Baptornis B. advenus Smoky Hill Chalk"Fragmentary skull [and] nearly complete postcranium.""Table 11.1," in Weishampel, et al. (2004). Page 215.Early Campanian A baptornithid hesperornithiform Guildavis G. tener Smoky Hill ChalkEarly Campanian Hesperornis Kansas"Partial postcranial skeleton." H. gracilis Kansas"Tarsometatarsus." H. regalis Kansas Smoky Hill ChalkEarly Campanian A large hesperornithid hesperornithiform Iaceornis I. marshi Smoky Hill ChalkEarly Campanian Ichthyornis I. agilis"Dinosaur distribution (Late Cretaceous; North America; Kansas; Niobrara Chalk Formation)." Weishampel, et al. (2004). Pp. 582. Kansas Junior synonym of I. dispar. I. anceps Kansas Junior synonym of I. dispar. I. dispar Kansas Smoky Hill ChalkLate Coniacian- Early Campanian An ichthyornithid I. lentus Kansas I. tener KansasEarly Campanian 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."Early Campanian

Mosasaurs

Mosasaurs 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.Everhart, M. J. 2002. New data on plesiosaur remains found as stomach contents of a Tylosaurus proriger (Squamata; Mosasauridae) from the Niobrara Formation of western Kansas. (Abstract) Transactions of the Kansas Academy of Science 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.Everhart, M. J. 2004. Late Cretaceous interaction between predators and prey. Evidence of feeding by two species of shark on a mosasaur. PalArch, vertebrate palaeontology series 1(1):1-7.