Paleobiota of the Niobrara Formation

Pachyrhizodus caninus skeletons (casts)

Pseudoperna congesta fossil osyters 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 the 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

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.

Bony fish

Other bony fish

Genus	Species	Member	Abundance	Notes
Lepisosteus[1]	Indeterminate[1]	Smoky Hill Chalk[1]		A lepisosteid gar
Paraliodesmus[2]	P. guadagnii[2]	Smoky Hill Chalk[2]		Amiiformes
Urenchelys[2]	U. abditus[2]	Smoky Hill Chalk[2]		Anguilliformes
Ferrifrons	F. rugosus			A ferrifronsid acanthomorph
Aethocephalichthys[2]	A. hyainarhinos[2]	Smoky Hill Chalk[2]		An actinopterygian of indeterminate classification[3]
Omosoma	O. garretti			A polymixiid actinopterygiian closely related to the modern Beardfish
Belonostomus[1]	Indeterminate[1]			Aspidorhynchiformes

Semionotiforms

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

Pycnodontiforms

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

Tsefeltiiforms

Genus	Species	Member	Abundance	Notes
Bananogmius	B. evolutus			A bananogmiid albuliform elopiform
Thryptodus[2]	T. zitteli[2]	Smoky Hill Chalk[2]		A tselfatiiform
Pentanogmius[2]	P. evolutus[2]	Smoky Hill Chalk[2]		A tselfatiiform

Salmoniforms

Genus	Species	Member	Abundance	Notes
Cimolichthys[2]	C. nepaholica[2]	Smoky Hill Chalk[2]		A cimolichthyid salmoniform protacanthopterygiian
Enchodus[2]	E. dirus[2]	Smoky Hill Chalk[2]		An enchodontid salmoniform protacanthopterygiian
	E. gladiolus[2]	Smoky Hill Chalk[2]
	E. petrosus[2]	Smoky Hill Chalk[2]
	E. shumardi[2]	Smoky Hill Chalk[2]

Alepisauriforms

Genus	Species	Member	Abundance	Notes
Apateodus[2]	Indeterminate[2]	Smoky Hill Chalk[2]		An alepisauriform actinopterygiian related to the modern lancetfish and lizardfish
Stratodus[2]	S. apicalis[2]	Smoky Hill Chalk[2]		An alepisauriform actinopterygiian
Leptecodon[2]	L. rectus			An alepisauriform actinopterygiian

Beryciforms

Genus	Species	Member	Abundance	Notes
Kansius[2]	K. sternbergi[2]	Smoky Hill Chalk[2]		A beryciform actinopterygiian
Trachichthyoides[2]	Indeterminate[2]	Smoky Hill Chalk[2]		A beryciform actinopterygiian
Caproberyx[2]	Indeterminate[2]	Smoky Hill Chalk[2]		A beryciform actinopterygiian

Pachycormiforms

Genus	Species	Member	Abundance	Notes	Images
Protosphyraena[1]	P. bentonianum			A primitive swordfish about 3m in length.	Protosphyraena perniciosa Xiphactinus audax Ichthyodectes ctenodon Gillicus arcuatus Saurodon leanus
	P. nitida[1]	Smoky Hill Chalk[1]
	P. perniciosa[1]	Smoky Hill Chalk[1]
	P. tenuis[1]	Smoky Hill Chalk[1]
	P. gladius[1]	Smoky Hill Chalk[1]		A misidentified pachycormid
Xiphactinus[2]	X. audax[2]	Smoky Hill Chalk[2]		A large ichthyodectid pachycormiform about 5m in length
Ichthyodectes[2]	I. ctenodon[2]	Smoky Hill Chalk[2]		An ichthyodectid pachycormiform about 2m in length
Gillicus[2]	G. arcuantus[2]	Smoky Hill Chalk[2]		An ichthyodectid pachycormiform about 2m in length
Saurodon[2]	S. leanus[2]	Smoky Hill Chalk[2]		A saurodontine ichthyodectid pachycormiform
Saurocephalus[2]	S. lanciformis[2]	Smoky Hill Chalk[2]		A saurodontine ichthyodectid pachycormiform
Prosaurodon[2]	P. pygmaeus[2]	Smoky Hill Chalk[2]

Crossognathiforms

Genus	Species	Member	Abundance	Notes	Images
Apsopelix[2]	A. anglicus[2]	Smoky Hill Chalk[2]		A crossognathiform about 12 cm in length
Martinichthys[2]	M. brevis[2]	Smoky Hill Chalk[2]		A crossognathiform
Niobrara[2]	N. encarsia[2]	Smoky Hill Chalk[2]		A crossognathiform
Zanclites[2]	Z. xenurus[2]	Smoky Hill Chalk[2]		A crossognathiform
Pachyrhizodus[2]	P. caninus[2]	Smoky Hill Chalk[2]		A crossognathiform
	P. leptopsis[2]	Smoky Hill Chalk[2]
	P. minimus[2]	Smoky Hill Chalk[2]

Cartilaginous fish

Fish are by far the most common fossils found from the formation, with remains of pehistoric 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[4]	C. mantelli[4]		Smoky Hill Chalk[4]		A large lamniform shark about 7m long
Cretalamna[5]	C. appendiculata[5]		Smoky Hill Chalk[5]		A lamniform shark about 2 to 3 meters long	Cretalamna appendiculata tooth from Israel
Cretolamna[4]	C. appendiculata[4]	N/A	N/A	N/A	An extremely widely used lapsus calami for Cretalamna.[6]
Johnlongia[4]	Indeterminate[4]		Smoky Hill Chalk[4]		An odontaspidid lamniform shark
Pseudocorax[4]	P. laevis[4]		Smoky Hill Chalk[4]		A lamniform shark smaller than Cretoxyrhina
Squalicorax[4]	S. falcatus[4]		Smoky Hill Chalk[4]		A lamniform shark about 5m long	Squalicorax falcatus tooth from Israel
	S. kaupi[4]		Smoky Hill Chalk[4]			Squalicorax kaupi tooth from Israel
	S. pristodontus[4]		Smoky Hill Chalk[4]
Scapanorhynchus[4]	S. raphiodon[4]		Smoky Hill Chalk[4]		A mitsukurinid shark similar in appearance to the modern day goblin shark	Scapanorhynchus raphiodon
Ptychodus[4]	P. anonymus[4]		Smoky Hill Chalk[4]		A ptychodontid hybodontoid shark
	P. martini[4]		Smoky Hill Chalk[4]
	P. mortoni[4]		Smoky Hill Chalk[4]
	P. occidentalis[4]		Smoky Hill Chalk[4]
	P. polygyrus[4]		Smoky Hill Chalk[4]

Other cartilaginous fish

Genus	Species	State	Member	Abundance	Notes	Images
Edaphodon	E. laqueatus				A callorhinchid chimaeriform related to the modern ratfish	Rhinobatos fossil
Rhinobatos[4]	R. incertus[4]		Smoky Hill Chalk[4]

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.^[7]

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.^[8][9] Most dinosaurs in the chalk were nodosaurs.

Non-avian

Genus	Species	State	Member	Material	Notes	Images
Claosaurus[10]	C. agilis[10]	Kansas[11]	Smoky Hill Chalk[10]	"Single articulated postcranial skeleton with associated skull fragments."[12]	A small hadrosaurid about 3.5m long.	Claosaurus agilis
Indeterminate hadrosaurid					A hadrosaurid of indeterminate classification about 9m in length. Possibly Corythosaurus
Niobrarasaurus[10]	N. coleii[10]	Kansas[11]	Smoky Hill Chalk[10]	"Partial skeleton."[13]	A nodosaurid ankylosaur.
Hierosaurus[10]	H. sternbergi[10]	Kansas[11]	Smoky Hill Chalk[10]	"Osteoderms."[14]	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[15]	A. celer[15]	Kansas[11] Nebraska[16]	Smoky Hill Chalk[15]	"Postcranial elements."[17]		Hesperornis regalis Ichthyornis dispar
Baptornis[15]	B. advenus[15]		Smoky Hill Chalk[15]	"Fragmentary skull [and] nearly complete postcranium."[18]	A baptornithid hesperornithiform about 1m long
Guildavis[15]	G. tener[15]		Smoky Hill Chalk[15]
Hesperornis[15]	H. crassipes[11]	Kansas[11]		"Partial postcranial skeleton."[18]
	H. gracilis[11]	Kansas[11]		"Tarsometatarsus."[18]
	H. regalis[15]	Kansas[11]	Smoky Hill Chalk[15]		A large hesperornithid hesperornithiform about 2m in length.
Iaceornis[15]	I. marshi[15]		Smoky Hill Chalk[15]
Ichthyornis[15]	I. agilis[11]	Kansas[11]			Junior synonym of I. dispar.[11]
	I. anceps[11]	Kansas[11]			Junior synonym of I. dispar.[11]
	I. dispar[15]	Kansas[11]	Smoky Hill Chalk[15]		An ichthyornithid about 60 cm long.
	I. lentus[11]	Kansas[11]
	I. tener[11]	Kansas[11]
	I. validus[11]	Kansas[11]			Junior synonym of I. dispar.[11]
	I. victor[11]	Kansas[11]			Junior synonym of I. dispar.[11]
Parahesperornis[15]	P. alexi[15]	Kansas[11]	Smoky Hill Chalk[15]	"Partial skull [and] complete postcranium."[18]

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[19]	C. undulatoplicatus[19]	Smoky Hill Chalk[19]			Volviceramus, Durania, and Pseudoperna.
Durania[19]	D. maxima[19]	Smoky Hill Chalk[19]
Haploscapha[20]		Fort Hays Limestone[20]
Inoceramus[20]		Fort Hays Limestone[20]
Ostrea[20]		Fort Hays Limestone[20]
Platyceramus[19]	P. platinus[19]	Smoky Hill Chalk[19]
Pseudoperna[19]	P. congesta[19]	Smoky Hill Chalk[19]
Volviceramus[19]	V. grandis[19]	Smoky Hill Chalk[19]

Cephalopods

Genus	Species	Member	Abundance	Notes	Images
Baculites[19]		Smoky Hill Chalk[19]			Baculites Tusoteuthis
Clioscaphites[19]		Smoky Hill Chalk[19]
Rugaptychus[19]		Smoky Hill Chalk[19]
Spinaptychus[19]		Smoky Hill Chalk[19]
Tusoteuthis[19]		Smoky Hill Chalk[19]

Echinoderms

Genus	Species	State	Member	Abundance	Notes
"Unitacrinus"[19]	"U. socialis"[19]	N/A	N/A	N/A	Common lapsus calami of Uintacrinus
Uintacrinus

Mosasaurs

Tylosaurus proriger specimen which was found with a plesiosaur in its stomach^[21]

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.^[22] 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.^[23]

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.^[24] Juveniles would have been vulnerable to predation by the many large mid-ocean predators, so it is likely that mosasaurs lived in groups rather than solitarily. Also, viviparous species tend to have much fewer offspring than egg-laying ones, so if there were few young that were born, they were most likely to have sought protection within groups in order to reach adulthood and thereby maintain the population of mosasaurs.

Genus	Species	Member	Abundance	Notes	Images
Tylosaurus[25]	T. nepaeolicus[25]	Smoky Hill Chalk[25]		A large tylosaurine about 15m long.	Tylosaurus proriger Anterolateral view of Platecarpus tympaniticus skull at the Peabody Museum of Natural History. Clidastes propython
	T. proriger[25]	Smoky Hill Chalk[25]
Platecarpus[25]	P. planifrons[25]	Smoky Hill Chalk[25]		A plioplatecarpine about 4.3m long
	P. tympaniticus[25]	Smoky Hill Chalk[25]
Clidastes[26]	C. liodontus[26]	Smoky Hill Chalk[26]		A small mosasaurine about 4m long
	C. prophython[26]	Smoky Hill Chalk[26]
Eonatator	E. sternbergii			A small halisaurine only 2.5m long
Halisaurus[25]	H. sternbergi[25]	Smoky Hill Chalk[25]
Ectenosaurus[25]	E. clidastoides[25]	Smoky Hill Chalk[25]

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.^[27] Plesiosaurs are rare in the formation and were therefore likely uncommon in the seas 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[28]	P. latipinnis[28]		Smoky Hill Chalk[28]	84.5-81.5 Ma ago[29]	A polycotylid.	Dolichorhynchops osborni Styxosaurus snowii Elasmosaurus platyurus
Dolichorhynchops[28]	D. osborni[28]		Smoky Hill Chalk[28]	84.5-81.5 Ma ago[29]	A polycotylid about 3m in length. also present in the Pierre Shale Formation
Thalassonomosaurus[20]	T. nobilis[20]	Kansas[20]	Fort Hays Limestone[20]
Brimosaurus[30]		Kansas[30]	Fort Hays Limestone[30]
Styxosaurus[28]	S. snowii[28]		Smoky Hill Chalk[28]	85-81.5 Ma ago[29]	A large elasmosaurid about 12m in length, also present in the Pierre Shale Formation
Elasmosaurus[28]	E. nobilis[20]	Kansas[20]	Fort Hays Limestone[20]		A large elasmosaurid about 14m in length.
	E. platyurus
	E. sternbergi[28]		Smoky Hill Chalk[28]

Pterosaurs

Two genre of pterosaurs are present in the formation. Both belong to the Pteranodontidae family of the suborder Pterodactyloidea. 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. Landing on all four limbs would have required both large pterosaurs to fold their wings back, thus reducing lift and making it a very difficult and improbable way of landing safely.^[31] One of the pterosaurs, Nyctosaurus, lacked all but the fourth phalanx of the hand, which is the extended finger that supports the wing membrane, meaning that quadrupedal locomotion on the ground would have been limited compared to other pterosaurs that were proficient at walking based on fossilized trackways that show both limbs in use on the ground.

Genus	Species	Member	Time span	Notes	Images
Nyctosaurus[32]	N. gracilis[32]	Smoky Hill Chalk[32]	85–84.5 Ma ago[29]	A pteranodontid Ornithocheiroid.	Nyctosaurus sp.
Pteranodon[32]	P. longiceps[32]	Smoky Hill Chalk[32]	86–84.5 Ma ago[29]	A large pteranodontid Ornithocheiroid with a wingspan of about 9m. Also present in the Pierre Shale.
	P. sternbergi[32]	Smoky Hill Chalk[32]	88–85 Ma ago[29]

Turtles

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[33]	B. barberi[33]	Smoky Hill Chalk[33]			Protostega gigas
Chelosphargis[33]	C. advena[33]	Smoky Hill Chalk[33]
Ctenochelys[33]	C. stenopora[33]	Smoky Hill Chalk[33]
Porthochelys[33]	P. laticeps[33]	Smoky Hill Chalk[33]		A toxichelid cryptodire
Protostega[33]	P. gigas[33]	Smoky Hill Chalk[33]		A protostegid cryptodire about 3m long
Toxochelys[33]	T. latiremis[33]	Smoky Hill Chalk[33]		A chelonioid cryptodire about 2m long

Footnotes

1. "Table 13.1: Bony Fish", Everhart (2005), page 244.
2. "Table 13.1: Bony Fish", Everhart (2005), page 245.
3. Fielitz, 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.
4. "Table 13.1: Sharks/Rays", Everhart (2005), page 244
5. "Table 13.1: Sharks/Rays," Everhart (2005), page 244. Note that Cretalamna is listed here under the widely used lapsus calami Cretolamna.
6. "Introduction", in "Skeletal and Dental Anatomy..." Shimada (2007), page 584
7. "Niobrarasaurus". Oceansofkansas.com. Retrieved 2016-04-13.
8. "Shark bit dino". Oceansofkansas.com. Retrieved 2016-04-13.
9. 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.
10. "Table 13.1: Dinosaurs", Everhart (2005), page 246.
11. "Dinosaur distribution (Late Cretaceous; North America; Kansas; Niobrara Chalk Formation)." Weishampel, et al. (2004). Pp. 582.
12. "Table 20.1," in Weishampel, et al. (2004). Page 439.
13. "Table 17.1," in Weishampel, et al. (2004). Page 367.
14. "Table 17.1," in Weishampel, et al. (2004). Page 368.
15. "Table 13.1: Birds," Everhart (2005), page 246.
16. "Dinosaur distribution (Late Cretaceous; North America; Nebraska; Niobrara Chalk Formation)." Weishampel, et al. (2004). Pp. 586.
17. "Table 11.1," in Weishampel, et al. (2004). Page 214.
18. "Table 11.1," in Weishampel, et al. (2004). Page 215.
19. "Table 13.1: Invertebrates," Everhart (2005), page 244.
20. "Material: YPM 1640," in "The Occurrence of Elasmosaurids..." Everhart (2006), page 172.
21. "Tylosaur food". Oceansofkansas.com. 2004-09-26. Retrieved 2016-04-13.
22. 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
23. 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.
24. Everhart, M. J. 2002. Remains of immature mosasaurs (Squamata; Mosasauridae) from the Niobrara Chalk (Late Cretaceous) argue against nearshore nurseries. (Abstract) Journal of Vertebrate Paleontology 22(suppl. to 3):52A.
25. "Table 13.1: Mosasaurs", Everhart (2005), page 246.
26. "Table 13.1: Mosasaurs", Everhart (2005), page 245.
27. "Field Guide, Part 3; Marine reptiles". Oceansofkansas.com. 2011-01-25. Retrieved 2016-04-13.
28. "Table 13.1: Plesiosaurs," Everhart (2005), page 245.
29. Carpenter, K. (2003). "Vertebrate Biostratigraphy of the Smoky Hill Chalk (Niobrara Formation) and the Sharon Springs Member (Pierre Shale)." High-Resolution Approaches in Stratigraphic Paleontology, 21: 421-437. doi:10.1007/978-1-4020-9053-0
30. "Material: YPM 1640," in "The Occurrence of Elasmosaurids..." Everhart (2006), page 173.
31. "Pteranodons". Oceansofkansas.com. 2011-01-21. Retrieved 2016-04-13.
32. "Table 13.1: Pterosaurs," Everhart (2005), page 246.
33. "Table 13.1: Turtles," Everhart (2005), page 245.

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. ISBN 0-520-24209-2.