Paleobiota of the Niobrara Formation

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[5]	C. mantelli[5]		Smoky Hill Chalk[5]		A large lamniform shark about 7m long
Cretalamna[6]	C. appendiculata[6]		Smoky Hill Chalk[6]		A lamniform shark about 2 to 3 meters long	Cretalamna appendiculata tooth from Israel
Cretolamna[5]	C. appendiculata[5]	N/A	N/A	N/A	An extremely widely used lapsus calami for Cretalamna.[7]
Johnlongia[5]	Indeterminate[5]		Smoky Hill Chalk[5]		An odontaspidid lamniform shark
Pseudocorax[5]	P. laevis[5]		Smoky Hill Chalk[5]		A lamniform shark smaller than Cretoxyrhina
Squalicorax[5]	S. falcatus[5]		Smoky Hill Chalk[5]		A lamniform shark about 5m long	Squalicorax falcatus tooth from Israel
	S. kaupi[5]		Smoky Hill Chalk[5]			Squalicorax kaupi tooth from Israel
	S. pristodontus[5]		Smoky Hill Chalk[5]
Scapanorhynchus[5]	S. raphiodon[5]		Smoky Hill Chalk[5]		A mitsukurinid shark similar in appearance to the modern day goblin shark	Scapanorhynchus raphiodon
Ptychodus[5]	P. anonymus[5]		Smoky Hill Chalk[5]		A ptychodontid hybodontoid shark
	P. martini[5]		Smoky Hill Chalk[5]
	P. mortoni[5]		Smoky Hill Chalk[5]
	P. occidentalis[5]		Smoky Hill Chalk[5]
	P. polygyrus[5]		Smoky Hill Chalk[5]

Other cartilaginous fish

Genus	Species	State	Member	Abundance	Notes	Images
Edaphodon	E. laqueatus				A callorhinchid chimaeriform related to the modern ratfish	Rhinobatos fossil
Rhinobatos[5]	R. incertus[5]		Smoky Hill Chalk[5]

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.[8]

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.[9][10] Most dinosaurs in the chalk were nodosaurs. The dinosaurs found here were endemic to Appalachia.[11]

Non-avian

Genus	Species	State	Member	Material	Notes	Images
Claosaurus[12]	C. agilis[12]	Kansas[13]	Smoky Hill Chalk[12]	"Single articulated postcranial skeleton with associated skull fragments."[14]	A small hadrosaurid about 3.5m long.	Claosaurus agilis
Indeterminate hadrosaurid[15]					A hadrosaurid of indeterminate classification about 9m in length. Possibly Corythosaurus.[15]
Niobrarasaurus[12]	N. coleii[12]	Kansas[13]	Smoky Hill Chalk[12]	"Partial skeleton."[16]	A nodosaurid ankylosaur.
Hierosaurus[12]	H. sternbergi[12]	Kansas[13]	Smoky Hill Chalk[12]	"Osteoderms."[17]	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[18]	A. celer[18]	Kansas[13] Nebraska[19]	Smoky Hill Chalk[18]	"Postcranial elements."[20]		Hesperornis regalis Ichthyornis dispar
Baptornis[18]	B. advenus[18]		Smoky Hill Chalk[18]	"Fragmentary skull [and] nearly complete postcranium."[21]	A baptornithid hesperornithiform about 1m long
Guildavis[18]	G. tener[18]		Smoky Hill Chalk[18]
Hesperornis[18]	H. crassipes[13]	Kansas[13]		"Partial postcranial skeleton."[21]
	H. gracilis[13]	Kansas[13]		"Tarsometatarsus."[21]
	H. regalis[18]	Kansas[13]	Smoky Hill Chalk[18]		A large hesperornithid hesperornithiform about 2m in length.
Iaceornis[18]	I. marshi[18]		Smoky Hill Chalk[18]
Ichthyornis[18]	I. agilis[13]	Kansas[13]			Junior synonym of I. dispar.[13]
	I. anceps[13]	Kansas[13]			Junior synonym of I. dispar.[13]
	I. dispar[18]	Kansas[13]	Smoky Hill Chalk[18]		An ichthyornithid about 60 cm long.
	I. lentus[13]	Kansas[13]
	I. tener[13]	Kansas[13]
	I. validus[13]	Kansas[13]			Junior synonym of I. dispar.[13]
	I. victor[13]	Kansas[13]			Junior synonym of I. dispar.[13]
Parahesperornis[18]	P. alexi[18]	Kansas[13]	Smoky Hill Chalk[18]	"Partial skull [and] complete postcranium."[21]

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[22]	C. undulatoplicatus[22]	Smoky Hill Chalk[22]			Volviceramus, Durania, and Pseudoperna.
Durania[22]	D. maxima[22]	Smoky Hill Chalk[22]
Haploscapha[23]		Fort Hays Limestone[23]
Inoceramus[23]		Fort Hays Limestone[23]
Ostrea[23]		Fort Hays Limestone[23]
Platyceramus[22]	P. platinus[22]	Smoky Hill Chalk[22]
Pseudoperna[22]	P. congesta[22]	Smoky Hill Chalk[22]
Volviceramus[22]	V. grandis[22]	Smoky Hill Chalk[22]

Cephalopods

Genus	Species	Member	Abundance	Notes	Images
Baculites[22]		Smoky Hill Chalk[22]			Baculites Enchoteuthis
Clioscaphites[22]		Smoky Hill Chalk[22]
Rugaptychus[22]		Smoky Hill Chalk[22]
Spinaptychus[22]		Smoky Hill Chalk[22]
Tusoteuthis[22]	T. longa	Smoky Hill Chalk[22]		A nomen dubium.[24]
Enchoteuthis	E. melanae	Smoky Hill Chalk		Most material formerly referred to Tusoteuthis now belongs to this taxon.[24]
	E. cobbani	Smoky Hill Chalk
Niobrarateuthis	N. bonneri	Smoky Hill Chalk

Tylosaurus proriger specimen which was found with a plesiosaur in its stomach[25]

Mosasaurs are the most common marine reptiles in the Niobrara Chalk and the most successful ones in the sea at the time. Four different genre 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.[26] 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.[27]

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.[28] 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
Tylosaurus[29]	T. nepaeolicus[29]	Smoky Hill Chalk[29]		A large tylosaurine, with the largest T. proriger reaching about 13 metres in length.	Tylosaurus nepaeolicus Anterolateral view of Platecarpus tympaniticus skull at the Peabody Museum of Natural History. Clidastes propython
	T. proriger[29]	Smoky Hill Chalk[29]
Platecarpus[29]	P. tympaniticus[29]	Smoky Hill Chalk[29]		A plioplatecarpine about 4.3m long
Plesioplatecarpus	P. planifrons[29]	Smoky Hill Chalk[29]
Clidastes[30]	C. liodontus[30]	Smoky Hill Chalk[30]		A nomen dubium.[31]
	C. prophython[30]	Smoky Hill Chalk[30]		A small mosasaurine about 4m long
Eonatator	E. sternbergii	Smoky Hill Chalk[30]		A small halisaurine only 2.5m long
Ectenosaurus[29]	E. clidastoides[29]	Smoky Hill Chalk[29]
	E. everhartorum[32]	Smoky Hill Chalk
Selmasaurus[33]	S. johnsoni	Smoky Hill Chalk

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.[34] 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[35]	P. latipinnis[35]		Smoky Hill Chalk[35]	84.5-81.5 Ma ago[36]	A polycotylid.	Styxosaurus snowii Elasmosaurus platyurus
Dolichorhynchops[35]	D. osborni[35]		Smoky Hill Chalk[35]	84.5-81.5 Ma ago[36]	A polycotylid about 3m in length. also present in the Pierre Shale Formation
Brimosaurus[37]	B. grandis	Kansas[37]	Fort Hays Limestone[37]		A nomen dubium.
Styxosaurus[35]	S. snowii[35]		Smoky Hill Chalk[35]	85-81.5 Ma ago[36]	A large elasmosaurid about 12m in length, also present in the Pierre Shale Formation
Elasmosaurus[35]	"E." sternbergi[35]		Smoky Hill Chalk[35]	84.5-81.5 Ma ago	Most likely not referable to Elasmosaurus.

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.[38]

Genus	Species	Member	Time span	Notes	Images
Nyctosaurus[39]	N. gracilis[39]	Smoky Hill Chalk[39]	85–84.5 Ma ago[36]	A nyctosaurid ornithocheiroid.	Nyctosaurus sp.
Pteranodon[39]	P. longiceps[39]	Smoky Hill Chalk[39]	86–84.5 Ma ago[36]	A large and very abundant pteranodontid ornithocheiroid.
Geosternbergia[40]	G. sternbergi	Smoky Hill Chalk	86–84.5 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.

Sea turtles have been found from the Niobrara Chalk that reached large sizes. The biggest, Archelon, attained a length of up to 4m, and was about 4.87m from flipper to flipper, 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[41]	B. barberi[41]	Smoky Hill Chalk[41]			Protostega gigas
Chelosphargis[41]	C. advena[41]	Smoky Hill Chalk[41]
Ctenochelys[41]	C. stenopora[41]	Smoky Hill Chalk[41]
Porthochelys[41]	P. laticeps[41]	Smoky Hill Chalk[41]		A toxichelid cryptodire
Protostega[41]	P. gigas[41]	Smoky Hill Chalk[41]		A protostegid cryptodire about 3m long
Toxochelys[41]	T. latiremis[41]	Smoky Hill Chalk[41]		A chelonioid cryptodire about 2m long

• 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. ISBN 0-520-24209-2.

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