Paleobiota of the Niobrara Formation

Color	Explanation
Light grey	A "regular" taxon which the scientific consensus does not regard as a dubious, synonymous, undescribed, or otherwise taxonomically questionable name.
Dark grey	A taxon or parataxon that is misidentified, dubious, synonymous, undescribed, or otherwise taxonomically questionable name.
Peach	An ichnotaxon, a parataxon representing a specific kind of trace fossil.
Light blue	An ootaxon, a parataxon representing a specific kind of fossil egg.
Light green	A morphotaxon, a parataxon representing a single stage or anatomical part of a plant or plant-like organism. Examples include fossil pine cones, fungal spores, and leaves.

Summarize Timeline Top Qs Fact Check

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.

Genus	Species	Member	Age	Abundance	Notes
Micropycnodon[1]	M. kansasensis[1]	Smoky Hill Chalk[1]	Late Coniacian-Satonian[1]		A pycnodontiform fish similar but unrelated to modern parrotfish

Genus	Species	Member	Abundance	Age	Notes
Hadrodus[1]	H. marshi[1]	Smoky Hill Chalk[1]		Early Campanian[1]	Family Hadrodontidae Thurmond and Jones 1981

Genus	Species	Member	Abundance	Age	Notes	Images
Protosphyraena[1]	P. bentonianum				A swordfish-like pachycormid
	P. nitida[1]	Smoky Hill Chalk[1]		Late Coniacian[1]
	P. perniciosa[1]	Smoky Hill Chalk[1]		Late Coniacian- Early Campanian?[1]
	P. tenuis[1]	Smoky Hill Chalk[1]		Santonian- Early Campanian[1]
	P. gladius[1]	Smoky Hill Chalk[1]			Named as a new genus, Bonnerichthys
Bonnerichthys[2]	B. gladius	Smoky Hill Chalk[3]		Late Coniacian- Early Campanian[1]	A filter feeding pachycormid

Genus	Species	Member	Abundance	Age	Notes	Images
Apsopelix[3]	A. anglicus[3]	Smoky Hill Chalk[3]		Late Coniacian- Early Campanian[1]	A crossognathid.
Pachyrhizodus[3]	P. caninus[3]	Smoky Hill Chalk[3]		Late Coniacian- Early Campanian[1]	A pachyrhizodontid
	P. leptopsis[3]	Smoky Hill Chalk[3]		Late Coniacian- Santonian[1]
	P. minimus[3]	Smoky Hill Chalk[3]		Late Coniacian- Early Campanian[1]

Genus	Species	Member	Abundance	Age	Notes	Images
Xiphactinus[3]	X. audax[3]	Smoky Hill Chalk[3]		Late Coniacian- Early Campanian[1]	A large ichthyodectid
Ichthyodectes[3]	I. ctenodon[3]	Smoky Hill Chalk[3]		Late Coniacian- Early Campanian[1]	An ichthyodectid
Gillicus[3]	G. arcuatus[3]	Smoky Hill Chalk[3]		Late Coniacian- Early Campanian[1]	A saurodontid
Saurodon[3]	S. leanus[3]	Smoky Hill Chalk[3]		Late Coniacian- Santonian[1]	A saurodontid
Saurocephalus[3]	S. lanciformis[3]	Smoky Hill Chalk[3]		Early Campanian[1]	A saurodontid
Prosaurodon[1]	P. pygmaeus[1]	Smoky Hill Chalk[1]		Santonian[1]

Genus	Species	Member	Abundance	Age	Notes	Images
Thryptodus[3]	T. zitteli[3]	Smoky Hill Chalk[3]		Late Coniacian[1]	A plethodid
Pentanogmius[3]	P. evolutus[3]	Smoky Hill Chalk[3]		Early Campanian[1]	A plethodid
Martinichthys[3]	M. brevis[3]	Smoky Hill Chalk[3]		Late Coniacian[1]	A plethodid
	M. xiphoides[3]	Smoky Hill Chalk[3]		Late Coniacian[1]
Niobrara[3]	N. encarsia[3]	Smoky Hill Chalk[3]		Santonian[1]	A plethodid
Zanclites[3]	Z. xenurus[3]	Smoky Hill Chalk[3]		Santonian[1]	A plethodid

Genus	Species	Member	Abundance	Age	Notes	Images
Cimolichthys[3]	C. nepaholica[3]	Smoky Hill Chalk[3]		Late Coniacian- Early Campanian[1]	A cimolichthyid
Enchodus[3]	E. dirus[3]	Smoky Hill Chalk[3]		Late Coniacian- Santonian[1]	An enchodontid
	E. gladiolus[3]	Smoky Hill Chalk[3]		Late Coniacian- Early Campanian[1]
	E. petrosus[3]	Smoky Hill Chalk[3]		Late Coniacian- Early Campanian[1]
	E. shumardi[3]	Smoky Hill Chalk[3]		Late Coniacian- Early Campanian[1]
Apateodus[3]	A. busseni[1]	Smoky Hill Chalk[3]		Early Campanian[1]	An alepisauriform actinopterygiian related to the modern lancetfish and lizardfish
	Indeterminate[3]			Santonian[1]
Stratodus[3]	S. apicalis[3]	Smoky Hill Chalk[3]		Late Coniacian- Early Campanian[1]	An alepisauriform actinopterygiian
Leptecodon[3]	L. rectus[citation needed]			Early Campanian[1]	An alepisauriform actinopterygiian

Genus	Species	Member	Abundance	Age	Notes
Kansius[3]	K. sternbergi[3]	Smoky Hill Chalk[3]		Early Campanian[1]	A beryciform actinopterygiian
Trachichthyoides[3]	Indeterminate[3]	Smoky Hill Chalk[3]		Santonian[1]	A beryciform actinopterygiian
Caproberyx[3]	Indeterminate[3]	Smoky Hill Chalk[3]		Santonian[1]	A beryciform actinopterygiian

Genus	Species	Member	Abundance	Age	Notes
Lepisosteus[1]	Indeterminate[1]	Smoky Hill Chalk[1]		Late Coniacian[1]	A lepisosteid gar
Paraliodesmus[3]	P. guadagnii[3]	Smoky Hill Chalk[3]		Late Coniacian- Santonian[1]	An amiiform
Urenchelys[3]	U. abditus[3]	Smoky Hill Chalk[3]		Santonian[1]	An anguilliform
Ferrifrons	F. rugosus				A ferrifronsid acanthomorph
Aethocephalichthys[3]	A. hyainarhinos[3]	Smoky Hill Chalk[3]		Late Coniacian- Early Campanian[1]	An actinopterygian of indeterminate classification[4]
Omosoma	O. garretti				A polymixiid actinopterygiian closely related to the modern Beardfish
Belonostomus[1]	Indeterminate[1]				An aspidorhynchid

Genus	Species	State	Member	Abundance	Age	Notes	Images
Cretoxyrhina[5]	C. mantelli[5]		Smoky Hill Chalk[5]		Late Coniacian- Early Campanian[5]	A large lamniform shark
Cretalamna[6]	C. appendiculata[6]		Smoky Hill Chalk[6]		Late Coniacian- Early Campanian[5]	A lamniform shark
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]		Late Coniacian[5]	An odontaspidid lamniform shark
Pseudocorax[5]	P. laevis[5]		Smoky Hill Chalk[5]		Late Coniacian- Santonian[5]	A lamniform shark smaller than Cretoxyrhina
Squalicorax[5]	S. falcatus[5]		Smoky Hill Chalk[5]		Late Coniacian- Santonian[5]	A lamniform
	S. kaupi[5]		Smoky Hill Chalk[5]		Santonian- Early Campanian[5]
	S. pristodontus[5]		Smoky Hill Chalk[5]		Early Campanian[5]
	S.microserratodon[5]				Late Coniacian[5]
Scapanorhynchus[5]	S. raphiodon[5]		Smoky Hill Chalk[5]		Late Coniacian[5]	A mitsukurinid shark similar in appearance to the modern day goblin shark
Ptychodus[5]	P. anonymus [5]		Smoky Hill Chalk[5]			A ptychodontid lamniform shark
	P. martini[5]		Smoky Hill Chalk[5]		Late Coniacian[5]
	P. mortoni[5]		Smoky Hill Chalk[5]		Late Coniacian- Santonian[5]
	P. occidentalis[5]		Smoky Hill Chalk[5]
	P. polygyrus[5]		Smoky Hill Chalk[5]

Genus	Species	State	Member	Abundance	Age	Notes	Images
Edaphodon[citation needed]	E. laqueatus[citation needed]					A callorhinchid chimaeriform related to the modern ratfish
Rhinobatos[5]	R. incertus[5]		Smoky Hill Chalk[5]		Late Coniacian- Early Campanian[5]

Summarize Timeline Top Qs Fact Check

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]

Genus	Species	State	Member	Material	Age	Notes	Images
Claosaurus[12]	C. agilis[12]	Kansas[13]	Smoky Hill Chalk[12]	"Single articulated postcranial skeleton with associated skull fragments."[14]	Early Campanian[12]	A small hadrosaurid
Indeterminate hadrosaurid[15]					Santonian[12]	A hadrosaurid of indeterminate classification. Possibly Corythosaurus.[15]
Niobrarasaurus[12]	N. coleii[12]	Kansas[13]	Smoky Hill Chalk[12]	"Partial skeleton."[16]	Late Coniacian- Santonian[12]	A nodosaurid ankylosaur.
Hierosaurus[12]	H. sternbergi[12]	Kansas[13]	Smoky Hill Chalk[12]	"Osteoderms."[17]	Late Coniacian[12]	A nodosaurid ankylosaur.

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	Age	Notes	Images
Apatornis[18]	A. celer[18]	Kansas[13] Nebraska[19]	Smoky Hill Chalk[18]	"Postcranial elements."[20]	Early Campanian[18]
Baptornis[18]	B. advenus[18]		Smoky Hill Chalk[18]	"Fragmentary skull [and] nearly complete postcranium."[21]	Early Campanian[18]	A baptornithid hesperornithiform
Guildavis[18]	G. tener[18]		Smoky Hill Chalk[18]		Early Campanian[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]		Early Campanian[18]	A large hesperornithid hesperornithiform
Iaceornis[18]	I. marshi[18]		Smoky Hill Chalk[18]		Early Campanian[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]		Late Coniacian- Early Campanian[18]	An ichthyornithid
	I. lentus[13]	Kansas[13]
	I. tener[13]	Kansas[13]			Early Campanian[18]
	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]	Early Campanian[18]

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.^[23] 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.^[24]

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.^[25] Juveniles would likely have been vulnerable to predation by the many large mid-ocean predators present in the ecosystem.

Genus	Species	Member	Abundance	Age	Notes	Images
Clidastes[26]	C. liodontus[26]	Smoky Hill Chalk[26]
	C. propython[26]	Smoky Hill Chalk[26]		Late Coniacian- Early Campanian[26]
Ectenosaurus[27]	E. clidastoides[27]	Smoky Hill Chalk[27]		Santonian[27]
	E. everhartorum[28]	Smoky Hill Chalk
	E. tlemonectes[29]	Smoky Hill Chalk		Late Coniacian?[30]
Eonatator	E. sternbergii	Smoky Hill Chalk[31][26]		Early Campanian[27]	A small halisaurine
Platecarpus[27]	P. tympaniticus[27]	Smoky Hill Chalk[27]			A plioplatecarpine
Plesioplatecarpus	P. planifrons[27]	Smoky Hill Chalk[27]		Late Coniacian- Santonian[26]
Tylosaurus[27]	T. nepaeolicus[27]	Smoky Hill Chalk[27]		Late Coniacian[27]	A large tylosaurine, with the largest T. proriger reaching about 13 metres in length.
	T. proriger[27]	Smoky Hill Chalk[27]		Santonian- Early Campanian[27]
Selmasaurus[32]	S. johnsoni	Smoky Hill Chalk		Santonian[26]

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.^[33] 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	Age	Notes	Images
Polycotylus[34]	P. latipinnis[34]		Smoky Hill Chalk[34]	84.5-81.5 Ma ago[35]	Early Campanian[34]	A polycotylid.
Dolichorhynchops[34]	D. osborni[34]		Smoky Hill Chalk[34]	84.5-81.5 Ma ago[35]	Early Campanian[34]	A polycotylid. also present in the Pierre Shale Formation
Brimosaurus[36]	B. grandis	Kansas[36]	Fort Hays Limestone[36]			A nomen dubium.
Styxosaurus[34]	S. snowii[34]		Smoky Hill Chalk[34]	85-81.5 Ma ago[35]	Santonian?- Early Campanian[34]	A large elasmosaurid, also present in the Pierre Shale Formation
Elasmosaurus[34]	"E." sternbergi[34]		Smoky Hill Chalk[34]	84.5-81.5 Ma ago	Early Campanian[34]	Most likely not referable to Elasmosaurus.

Two genera 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.^[37]

Genus	Species	Member	Time span	Age	Notes	Images
Nyctosaurus[38]	N. gracilis[38]	Smoky Hill Chalk[38]	85–84.5 Ma[35]	Santonian- Early Campanian[38]	A nyctosaurid ornithocheiroid
Pteranodon[38]	P. longiceps[38]	Smoky Hill Chalk[38]	86–84.5 Ma[35]	Santonian- Early Campanian[38]	A large and very abundant pteranodontid ornithocheiroid
	P. sternbergi	Smoky Hill Chalk	86–84.5 Ma	Late Coniacian[38]	Considered to be a distinct genus Geosternbergia by a few paleontologists, although most regard it as a species of Pteranodon

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	Age	Notes	Images
Bothremys[39]	B. barberi[39]	Smoky Hill Chalk[39]		Early Campanian[39]
Chelosphargis[39]	C. advena[39]	Smoky Hill Chalk[39]		Late Coniacian[39]	archelon-a giant sea turtle
Ctenochelys[39]	C. stenopora[39]	Smoky Hill Chalk[39]		Santonian[39]
Kansastega[40]	K. copei[39]				A protostegid cryptodire formerly a synonym of Protostega gigas
Porthochelys[39]	P. laticeps[39]	Smoky Hill Chalk[39]		Late Coniacian[39]	A toxichelid cryptodire
Protostega[39]	P. gigas[39]	Smoky Hill Chalk[39]		Early Campanian[39]	A protostegid cryptodire
Toxochelys[39]	T. latiremis[39]	Smoky Hill Chalk[39]		Late Coniacian- Early Campanian[39]	A chelonioid cryptodire