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Paleobiota of the Niobrara Formation

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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[edit]

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[edit]


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


Genus Species Member Abundance Notes


H. marshi[1] Smoky Hill Chalk[1] Family Hadrodontidae Thurmond and Jones 1981


Genus Species Member Abundance Notes Images
Protosphyraena[1] P. bentonianum A swordfish-like pachycormid
Protosphyraena perniciosa
Bonnerichthys gladius
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] Named as a new genus, Bonnerichthys
Bonnerichthys[2] B. gladius Smoky Hill Chalk[3] A filter feeding pachycormid


Genus Species Member Abundance Notes Images
Apsopelix[3] A. anglicus[3] Smoky Hill Chalk[3] A crossognathid.
Pachyrhizodus sp.
Pachyrhizodus[3] P. caninus[3] Smoky Hill Chalk[3] A pachyrhizodontid
P. leptopsis[3] Smoky Hill Chalk[3]
P. minimus[3] Smoky Hill Chalk[3]


Genus Species Member Abundance Notes Images
Xiphactinus[3] X. audax[3] Smoky Hill Chalk[3] A large ichthyodectid
Xiphactinus audax
Ichthyodectes ctenodon
Gillicus arcuatus
Saurodon leanus
Ichthyodectes[3] I. ctenodon[3] Smoky Hill Chalk[3] An ichthyodectid
Gillicus[3] G. arcuantus[3] Smoky Hill Chalk[3] A saurodontid
Saurodon[3] S. leanus[3] Smoky Hill Chalk[3] A saurodontid
Saurocephalus[3] S. lanciformis[3] Smoky Hill Chalk[3] A saurodontid


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


Genus Species Member Abundance Notes Images
Cimolichthys[3] C. nepaholica[3] Smoky Hill Chalk[3] A cimolichthyid
Cimolichthys nepaholica
Enchodus petrosus


E. dirus[3] Smoky Hill Chalk[3] An enchodontid
E. gladiolus[3] Smoky Hill Chalk[3]
E. petrosus[3] Smoky Hill Chalk[3]
E. shumardi[3] Smoky Hill Chalk[3]
Apateodus[3] Indeterminate[3] Smoky Hill Chalk[3] An alepisauriform actinopterygiian related to the modern lancetfish and lizardfish
Stratodus[3] S. apicalis[3] Smoky Hill Chalk[3] An alepisauriform actinopterygiian
Leptecodon[3] L. rectus[citation needed] An alepisauriform actinopterygiian


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

Other bony fish[edit]

Genus Species Member Abundance Notes


Indeterminate[1] Smoky Hill Chalk[1] A lepisosteid gar
Paraliodesmus[3] P. guadagnii[3] Smoky Hill Chalk[3] An amiiform
Urenchelys[3] U. abditus[3] Smoky Hill Chalk[3] An anguilliform
Ferrifrons F. rugosus A ferrifronsid acanthomorph
Aethocephalichthys[3] A. hyainarhinos[3] Smoky Hill Chalk[3] An actinopterygian of indeterminate classification[4]
Omosoma O. garretti A polymixiid actinopterygiian closely related to the modern Beardfish
Belonostomus[1] Indeterminate[1] An aspidorhynchid

Cartilaginous fish[edit]

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 State Member Abundance Notes Images


C. mantelli[5] Smoky Hill Chalk[5] A large lamniform shark


C. appendiculata[6] Smoky Hill Chalk[6] A lamniform shark
Cretalamna appendiculata tooth from Israel


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
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 lamniform 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[edit]

Genus Species State Member Abundance Notes Images

Edaphodon[citation needed]

E. laqueatus[citation needed]

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]


Genus Species State Member Material Notes Images


C. agilis[12]

Kansas[13] Smoky Hill Chalk[12]

"Single articulated postcranial skeleton with associated skull fragments."[14]

A small hadrosaurid
Claosaurus agilis
Indeterminate hadrosaurid[15] A hadrosaurid of indeterminate classification. Possibly Corythosaurus.[15]


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.


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] 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
Guildavis[18] G. tener[18] Smoky Hill Chalk[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
Iaceornis[18] I. marshi[18] Smoky Hill Chalk[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
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.


Genus Species Member Abundance Notes Images


C. undulatoplicatus[22]

Smoky Hill Chalk[22]
Volviceramus, Durania, and Pseudoperna.


D. maxima[22]

Smoky Hill Chalk[22]


Fort Hays Limestone[23]


Fort Hays Limestone[23]
Ostrea[23] Fort Hays Limestone[23]


P. platinus[22]

Smoky Hill Chalk[22]


P. congesta[22]

Smoky Hill Chalk[22]


V. grandis[22] Smoky Hill Chalk[22]


Genus Species Member Abundance Notes Images


Smoky Hill Chalk[22]
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


Genus Species State Member Abundance Notes
"Unitacrinus"[22] "U. socialis"[22] N/A N/A N/A Common lapsus calami of Uintacrinus


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. 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.[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


C. liodontus[29] Smoky Hill Chalk[29]
C. prophython[29] Smoky Hill Chalk[29]


E. clidastoides[30] Smoky Hill Chalk[30]
E. everhartorum[31] Smoky Hill Chalk
E. tlemonectes[32] Smoky Hill Chalk
Eonatator E. sternbergii Smoky Hill Chalk[33][29] A small halisaurine
Platecarpus[30] P. tympaniticus[30] Smoky Hill Chalk[30] A plioplatecarpine
Tylosaurus nepaeolicus
Anterolateral view of Platecarpus tympaniticus skull at the Peabody Museum of Natural History.
Clidastes propython
Plesioplatecarpus P. planifrons[30] Smoky Hill Chalk[30]


T. nepaeolicus[30]

Smoky Hill Chalk[30] A large tylosaurine, with the largest T. proriger reaching about 13 metres in length.
T. proriger[30] Smoky Hill Chalk[30]
Selmasaurus[34] 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.[35] 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


P. latipinnis[36] Smoky Hill Chalk[36] 84.5-81.5 Ma ago[37] A polycotylid.
Styxosaurus snowii
Elasmosaurus platyurus
Dolichorhynchops[36] D. osborni[36] Smoky Hill Chalk[36] 84.5-81.5 Ma ago[37] A polycotylid. also present in the Pierre Shale Formation
Brimosaurus[38] B. grandis Kansas[38] Fort Hays Limestone[38] A nomen dubium.
Styxosaurus[36] S. snowii[36] Smoky Hill Chalk[36] 85-81.5 Ma ago[37] A large elasmosaurid, also present in the Pierre Shale Formation
Elasmosaurus[36] "E." sternbergi[36] Smoky Hill Chalk[36] 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.[39]

Genus Species Member Time span Notes Images


N. gracilis[40]

Smoky Hill Chalk[40] 85–84.5 Ma ago[37] A nyctosaurid ornithocheiroid.
Nyctosaurus sp.


P. longiceps[40] Smoky Hill Chalk[40] 86–84.5 Ma ago[37] A large and very abundant pteranodontid ornithocheiroid.


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, 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


B. barberi[42]

Smoky Hill Chalk[42]
Protostega gigas
Chelosphargis[42] C. advena[42] Smoky Hill Chalk[42]


C. stenopora[42]

Smoky Hill Chalk[42]
Porthochelys[42] P. laticeps[42] Smoky Hill Chalk[42] A toxichelid cryptodire
Protostega[42] P. gigas[42] Smoky Hill Chalk[42] A protostegid cryptodire
Toxochelys[42] T. latiremis[42] Smoky Hill Chalk[42] A chelonioid cryptodire


  1. ^ a b c d e f g h i j k l m n o p q r s t "Table 13.1: Bony Fish", Everhart (2005), page 244.
  2. ^ Viegas, Jennifer (18 February 2010), SUV-Sized Fish Were Earliest Filter-Feeders, Discovery News, retrieved 1 April 2010
  3. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai aj ak al am an ao ap aq ar as at au av aw ax ay az ba bb bc bd be bf bg bh bi bj bk bl bm bn bo bp bq br bs bt bu bv bw bx by bz ca cb "Table 13.1: Bony Fish", Everhart (2005), page 245.
  4. ^ 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.
  5. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag ah ai "Table 13.1: Sharks/Rays", Everhart (2005), page 244
  6. ^ a b c "Table 13.1: Sharks/Rays," Everhart (2005), page 244. Note that Cretalamna is listed here under the widely used lapsus calami Cretolamna.
  7. ^ "Introduction", in "Skeletal and Dental Anatomy..." Shimada (2007), page 584
  8. ^ "Niobrarasaurus". Oceansofkansas.com. Retrieved 2016-04-13.
  9. ^ "Shark bit dino". Oceansofkansas.com. Retrieved 2016-04-13.
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  11. ^ Brownstein, Chase D. (February 2018). "The biogeography and ecology of the Cretaceous non-avian dinosaurs of Appalachia". Palaeontologia Electronica. 21 (1.5A): 1–56. doi:10.26879/801. Retrieved 21 March 2021.
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  14. ^ "Table 20.1," in Weishampel, et al. (2004). Page 439.
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  20. ^ "Table 11.1," in Weishampel, et al. (2004). Page 214.
  21. ^ a b c d "Table 11.1," in Weishampel, et al. (2004). Page 215.
  22. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa "Table 13.1: Invertebrates," Everhart (2005), page 244.
  23. ^ a b c d e f "Material: YPM 1640," in "The Occurrence of Elasmosaurids..." Everhart (2006), page 172.
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  32. ^ Kiernan, Caitlin R.; Ebersole, Jun A. (2023). "Two new plioplatecarpine mosasaurs (Mosasauridae; Plioplatecarpinae) of the genus Ectenosaurus from the Upper Cretaceous of North America". PaleoBios. 40 (13). doi:10.5070/P9401362375. ISSN 0031-0298.
  33. ^ Bardet N, Suberbiola P, Iarochene M, Bouya B, Amaghzaz M (2005). "A new species of Halisaurus from the Late Cretaceous phosphates of Morocco, and the phylogenetical relationships of the Halisaurinae (Squamata: Mosasauridae)". Zoological Journal of the Linnean Society. 143 (3): 447–472. doi:10.1111/j.1096-3642.2005.00152.x.
  34. ^ Polcyn, M. J., and Everhart, M. J., 2008, Description and phylogenetic analysis of a new species of Selmasaurus (Mosasauridae: Plioplatecarpinae) from the Niobrara Chalk of western Kansas: In: Proceedings of the Second Mosasaur Meeting, edited by Everhart, M. J, Fort Hays Studies, Special Issue number 3, p. 13-28.
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  37. ^ a b c d e 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
  38. ^ a b c "Material: YPM 1640," in "The Occurrence of Elasmosaurids..." Everhart (2006), page 173.
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  41. ^ "Geosternbergia". Pteros. Pteros. Retrieved 28 August 2022.
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  • 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.