Grayscale photo of Uintacrinus, a cretaceous stalkless crinoid, slowing the calices and arms.

Fossils of the Great Plains

Simple map showing the Great Plains region of the South Central United States, including portions of Texas, Oklahoma, and Kansas.

Page snapshot: Introduction to the fossils of the Great Plains region of the south-central United States.


Topics covered on this page: Mesozoic fossils; Triassic and Jurassic fossils; Cretaceous fossils of Kansas; Cretaceous fossils of Oklahoma and Texas; Cenozoic fossils; Resources.

Credits: Most of the text on this page comes from "Fossils of the South Central US" by Warren D. Allmon and Alex F. Wall, chapter 3 in the The Teacher-Friendly Guide to the Geology of the South Central USedited by Mark D. Lucas, Robert M. Ross, and Andrielle N. Swaby (published in 2015 by the Paleontological Research Institution; currently out of print). The book was adapted for the web by Elizabeth J. Hermsen and Jonathan R. Hendricks in 2022. Changes include formatting and revisions to the text and images. Credits for individual images are given in figure captions.

Updates: Page last updated February 16, 2022.

Image above: Close up of a group of crinoids (Uintacrinus socialis) from the Cretaceous Niobrara Chalk, Kansas. Photo by James St. John (flickr, Creative Commons Attribution 2.0 Generic license, image cropped and resized).

Mesozoic fossils

The Great Plains of Texas, Oklahoma, and Kansas are dominated by mid to late Mesozoic- and Cenozoic-aged rocks. Little of the bedrock in the region is older than 145 million years.

Triassic and Jurassic

The Triassic rocks of Texas crop out along the border between the Great Plains and Central Lowland regions. A variety of early dinosaurs are found in here, along with phytosaurs (extinct animals that look like crocodiles, although the two groups are not related) and synapsids (mammal-like reptiles). Triassic fossils from this region are covered on the Fossils of the Central Lowland and Interior Highlands page.

The Jurassic is not well represented in this region. However, the western panhandle of Oklahoma includes a small but important exposure of terrestrial shales and sandstones, which contain turtles, crocodiles, freshwater fish, and Oklahoma’s state fossil, the large allosaur Saurophaganax.


Photograph of a skeleton of Postosuchus on display at a museum. The animal was predatory, bipedal and had a relatively large head.

Postosuchus kirkpatricki, a Triassic archosaur first described from material found at the Post Quarry site, Garza County, Texas. Photo of a specimen on display at the Museum of Texas Tech University by Dallas Krentzel (Wikimedia Commons, Creative Commons Attribution 2.0 Generic license, image cropped and resized).


2-Panel figure of Saurophaganax. Panel 1: Photo of a mounted skeleton on display in a museum. Panel 2: Illustration reconstructing what the predatory dinosaur may have looked like in life.

Saurophaganax maximusLeft: Mounted skeleton at the Oklahoma Museum of Natural History. Image from "Friday phalanges: Megaraptor vs. Saurophaganax" by Matt Wedel (SV-Pow, Creative Commons Attribution 3.0 Unported license, image cropped and resized). Right: Reconstruction of what Saurphaganax may have looked like in by Mario Lanzas (Wikimedia Commons, Creative Commons Attribution-Share Alike 4.0 International license, image cropped).


Cretaceous

Cretaceous fossils of Kansas

The Cretaceous rocks of Kansas contain abundant remains of late Mesozoic marine life, including some of the best fossils in the world from this time period. Fossils of marine invertebrates indicate that a warm, shallow sea covered the western part of the state, while terrestrial plant fossils and coal seams in central Kansas represent near-shore wetlands. These wetlands mark the shore of the great Western Interior Seaway, which divided North America into two landmasses as it extended from the Gulf of Mexico to the Arctic Ocean. The flat floor of this inland sea provided the basis for the modern topography of the Interior Plains.


Map of the Western Interior Seaway. The map showing the seaway extending across North America from the Gulf of Mexico to the Arctic Ocean. Laramidia occurs to the west of the seaway and Appalachia to the east. The Hudson Seaway branches off the Western Interior Seaway to the northeast, covering modern-day Manitoba and Hudson Bay.

Extent of the Western Interior Seaway during the Cretaceous Period. Image from Cretaceous Atlas of Ancient Life: Western Interior Seaway (Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International license).


Photograph of a three-lobed leaf attributed to Sassafras from the Late Cretaceous of Kansas.

Leaf of a sycamore tree (Platanus), Early Cretaceous, Dakota Sandstone, Saline County, Kansas. Photo of YPM PB 040687 by Tsveta Ivanova, 2020 (Yale Peabody Museum of Natural History/YPM, CC0 1.0 Universal/Public Domain Dedication, accessed via GBIF.org).


Photos of fossil leaves from the Dakota Formation of Kanas, including cordate of oval floating leaves of aquatic plants and a compound leaf from a tree or shrub with three leaflets.

Angiosperm (flowering plant) leaf fossils from the Lower Cretaceous Dakota Formation, Barton County, Kansas. Left: Leaves of aquatic plants, including Aquatifolia fluitans (1, 2, scale bar = 5 millimeters) and Brasenites kansense (3, 4, scale bar = 1 centimeter). Right: Compound leaf of Sapindopsis powelliana (scale bar = 1 centimeter) Source: Figures 5 and 16 from H. Wang and D. L. Dilcher (2018) Palaeontologia Electronica 21.3.34A (Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International license).


Some spectacular fossils, notably ammonites, occur in the Late Cretaceous Carlile Shale that occurs in a northeast-to-southwest oriented exposure in central Kansas. The most well-known Cretaceous fossils, however, are found in western Kansas chalk, a carbonate rock made up primarily of the fossils of microscopic marine algae called coccolithophores. Today, chalk accumulates mainly in the deep sea. During the Cretaceous, when sea levels were much higher than today, chalk accumulated in shallow inland seas in both North America and Europe; these shallow seas were only about 100–300 meters (328–984 feet) deep. The Cretaceous period is named for the abundance of chalk that accumulated during this time (the Latin word for chalk is creta).


Photos showing a side and end view of an ammonite with a typical coiled shell.
Photos showing outer views and long sections of the shell of a loosely coiled ammonite.
Panoramic photograph of Monument Rocks in Kansas.

Outcroppings of the Cretaceous Niobrara Formation at Monument Rocks in western Kansas. Photograph by Vincent Parsons (FlickrCreative Commons Attribution-NonCommercial 2.0 Generic license; image cropped and resized).


In the Western Interior Seaway, chalk formed in marine environments with relatively little wave or current energy, and on seafloors where dissolved oxygen concentrations were low. This led to conditions that were not particularly favorable for bottom-living organisms, but that were exceptionally good for preserving whatever died there.

The Niobrara Chalk Formation of Kansas—especially its Smoky Hill Chalk Member (a member is a subdivision of a formation)—is famous for its spectacularly preserved marine vertebrates, including mosasaurs, plesiosaurs, giant turtles, sharks, and other fishes (such as the enormous Xiphactinus). It also preserves pterosaurs (an extinct group of flying reptiles), and diving birds. Interestingly, coprolites (fossilized feces) are also fairly common.

The few benthic (seafloor-dwelling) organisms that were able to tolerate the low oxygen levels include the stalkless crinoid Uintacrinus as well as rudist and inoceramid bivalves. Other invertebrates include ammonoids and gastropods. 


Photograph of the skeleton of the mosasaur Platecarpus. Mosasaurs have four paddle-like feet and large heads with pointed teeth. They also have long tails.

Skeleton of Platecarpus tympaniticus, a mosasaur from the Niobrara Chalk of Logan County, Kansas. Scale bar is 0.5 meters (about 1.6 feet), specimen is 5.67 meters (about 18.6 feet) long. Photo of specimen LACM 128319, specimen in the collections of the Natural History Museum of Los Angeles County, fig. 1 from J. Lindgren, M. W. Caldwell, T. Konishi, and L. M. Chiappe (2010) PLoS ONE 5(8): E11998 (Creative Commons Attribution license).


Photo of the narrow, elongated skull of the mosasaur Clidastes with many pointed teeth.

Skull of Clidastes liodontus, a mosasaur from the Niobrara Chalk of Logan County, Kansas. Photo of specimen NMNH V11719, National Museum of Natural History, Paleobiology Department, Smithsonian Institution (public domain).


Photo of the mounted skeleton of the plesiosaur Dolichorhynchops on display. The skeleton has an elongated skull and four large flipper-like feet. The neck is somewhat elongated.

Skeleton of Dolichorhynchops osborni, a plesiosaur from the Niobrara Chalk of Logan County, Kansas. Photo of Sternberg Museum (Fort Hayes, Kansas) display specimen FHSMVP 404 by Jonathan R. Hendricks ([email protected], Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License).


Photo of the skull of the elasmosaur Styxosaurus. Elasmosaurs had long necks and four paddle-like legs. The skull has pointed teeth that overlap the jaws when the mouth is shut.
2-panel image, photos of skeletons of the giant Cretaceous sea turtle Protostega. Panel 1: View showing the back of the turtle. Panel 2: Underside of a turtle.

Two views of Protostega gigas, from above (left) and below (right). This turtle could grow up to about 3.7 meters (12 feet) long and weigh up to about 900 kilograms (2000 pounds)! The specimen on the left is from the Niobrara Chalk in Gove County, Kansas. The specimen on the right is a reproduction (no locality for the original given, but probably Niobrara Chalk). Photo credit, left image: RaviSarma (Wikimedia Commons, Creative Commons Attribution-ShareAlike 3.0 unported license, image cropped and resized). Photo credit, right image: McDinosaurhunter (Wikimedia Commons, Creative Commons Attribution-ShareAlike 3.0 unported license, image cropped and resized).


Photo of a chunk of rock from the Niobrara Formation with many shark teeth embedded in the surface.

Shark teeth and fish bones, Niobrara Formation, Kansas. Photo by James St. John (flickr, Creative Commons Attribution 2.0 Generic license, image cropped and resized).


Photograph of the skeleton of the giant predatory fish Xipactinus on display in a museum. Inside the ribs of the skeleton is the skeleton of another smaller fish.

Large fish (Xiphactinus audax) with a small fish preserved in its gut. This famous "fish-within-a-fish" specimen was excavated by the fossil collector George Sternberg from the Niobrara Chalk, Gove County, Kansas, in 1952. It is on display at the Sternberg Museum in Fort Hayes, Kansas. Photo of FSHVP 333 from Cretaceous Atlas of Ancient Life: Western Interior Seaway (Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License).


Photo of a specimen of pteranodon, a pterosaur, with a long, beak-like mouth, short crest, long neck, and wing bones.

A pterosaur (Pteranodon occidentalis) from the Cretaceous Niobrara Chalk, Logan County, Kansas. Source: Smithsonian National Museum of Natural History specimen USNM V12167 (public domain).


Photo of a skeleton of Hesperornis, a Cretaceous diving bird, on display at a museum.

A bird (Hesperornis regalis) from the Cretaceous Niobrara Chalk, Logan County, Kansas. Source: Smithsonian National Museum of Natural History specimen USNM V4978 (public domain).


Photos of a slab of Uintacrinus, a Cretaceous stalkless crinoid. Each animal consists of a calyx and arms.
Photo of a group of rudist bivalves. The bivalves look like a chunk of rock with large circular holes on the upper side.

Rudist bivalves (Durania maxima) from the Niobrara Chalk (Smoky Hill Member), Kansas. Rudists are a group of bizarre reef-forming bivalves. This specimen includes 21 different animals. In life, each would have had a "lid" formed by the second part (valve) of the shell. Photo of Sternberg Museum (Fort Hayes, Kansas) display specimen FHSMIP 1136 by Jonathan R. Hendricks ([email protected], Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License).


2-panel image showing photos of Cretaceous oyster shells. Panel 1: A single giant oyster on display. Panel 2: Small oyster shells encrusting the shell of a larger oyster.

Oysters from the Niobrara Chalk, Kansas. Left: A giant oyster (Platyceramus platinus). Specimen on display at the Denver Museum of Nature and Science (Colorado), photo by Jonathan R. Hendricks ([email protected], Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License). Right: A portion of a giant oyster (Platyceramus platinus) shell encrusted with smaller oysters (Pseudoperna cogesta) taken in the field at the Castle Rock chalk badlands. Photo by and information from James St. John (flickr, Creative Commons Attribution 2.0 Generic license, image cropped and resized).


Cretaceous fossils of Oklahoma and Texas

In Texas, extensive Cretaceous outcrops are preserved in the Edwards Plateau. There, limestone units produce a host of marine invertebrate fossils. Ammonoids, gastropods, bivalves (including reef-forming rudists), echinoderms, corals, and petrified wood (in layers formed on or near land) may also be found. Rare fossil fish, dinosaur, pterosaur, and various marine reptile bones have been found along the Great Plains side of the Balcones Escarpment.


Photographs showing four views (top, bottom, front, and back or hinge) of a fossil bivalve from the Cretaceous of Texas. The shell is relatively smooth.

The bivalve Arctica compacta from the Upper Cretaceous Buda Limestone Formation, Travis County, Texas. Photo of UT 40526 from the Cretaceous Atlas of Ancient Life, Western Interior Seaway (Creative Commons Attribution NonCommercial-ShareAlike 4.0 International license, image modified).


Two views of an ammonoid (both from the side) for the Late Cretaceous Edwards Plateau region of Texas. This ammonoid has a loosely spiraling shell.

The ammonoid Hypoturrilites tuberculatus from the Upper Cretaceous Buda Limestone Formation, Travis County, Texas. Photo of UT 42852 from the Cretaceous Atlas of Ancient Life, Western Interior Seaway (Creative Commons Attribution NonCommercial-ShareAlike 4.0 International license, image modified).


Two views of a fossil echinoderm from the Late Cretaceous of the Edwards Plateau region of Texas. The animal is ovoid with bilateral symmetry. When viewed from above, five furrows are visible radiating from a central point.

The most famous fossil remains in this area, however, are dinosaur trackways found in more than a dozen locations on and north of the Edwards Plateau. The variety of footprints is attributed to theropods, ornithiscians, and sauropods, though the precise species are impossible to know. Some of the theropod footprints may have been made by Acrocanthosaurus, one of the largest known carnivorous dinosaurs. Skeletal remains of Acrocanthosaurus have been found in Lower Cretaceous rocks in Oklahoma, Texas, and Wyoming (see a picture of an Acrocanthosaurus skeleton on the South-central U.S.: Fossils of the Coastal Plain page).


Map showing locations of dinosaur trackway sites in Texas. These sites are clustered in the central and southern parts of the state.

Sites in Texas where dinosaur footprints are known. Map by Wade-Greenberg-Brand, originally published in The Teacher-Friendly Guide to the Earth Science of the South Central US.


Photograph of a three-toed dinosaur footprint from the Cretaceous of Texas with water in the low areas of the print.

The therpod dinosaur track, Dinosaur Valley State Park, Glen Rose, Texas. Photo by Diane Turner (Wikimedia Commons, Creative Commons Attribution 2.0 Generic license, image cropped and resized).


Digital fly-through of a trackway on the Paluxy River that was excavated by Roland T. Bird in 1940. This trackway is interpreted as preserving a chase, with a predatory theropod dinosaur chasing a saurpod (long-necked herbivorous dinosaur). The trackway was about 9 meters (about 29.5 feet) long. This movie was made using historical photos; after the photos were taken, the tracks were removed and distributed to museums. Move S1 from P. L. Falkingham, K. T. Bates, and J. O. Farlow (2014) PLoS ONE 9(4): e93247 (via Figshare, Creative Commons Attribution 4.0 International license).

Cenozoic fossils

In the Late Cretaceous, the Western Interior Seaway retreated and the Rocky Mountains rose to the west; streams carried gravel, sand, and silt that eroded from these newly formed mountains. The sediments filled wide, shallow valleys to create a broad, gently dipping plain that contains a variety of terrestrial and freshwater fossils, including gastropods, clams, algae, and the occasional plant.

By the middle Eocene, the environment became wetter and cooler. Mammals were the dominant animals on land, including a mix of extinct, extirpated, and extant animals that would look out of place in North America today. The Miocene-Pliocene Ogallala Group of Kansas and Oklahoma has produced abundant remains of rodents, horses, and land tortoises, among others.

Pleistocene deposits of central Texas have yielded the bones of sloths and glyptodonts, among other forms.


Photo of a skeleton of an extinct North American rhino from the Miocene of Kansas on display in a museum.

An extinct North American rhinoceros (Teleoceras fossiger), Miocene, Kansas. Photo by James St. John (flickr, Creative Commons Attribution 2.0 Generic license, image resized).


Photos showing two views of a gomphothere skull from the Miocene of Texas. Gomphotheres are related to elephants, but they have a projecting lower jaw. An overall view and a detail of the lower jaw and upper tusks are shown.

Skull of a gomphothere, an extinct animal related to elephants, from the Miocene, Clarendon region, Texas. Photos of specimen on display in the Cleveland Museum of Natural History, Ohio. Left photo and right photo by James St. John (flickr, Creative Commons Attribution 2.0 Generic license, images cropped and resized).

Resources

Resources from the Paleontological Research Institution & partners

Cretaceous Atlas of Ancient Life, Western Interior Seaway (Colorado, Iowa, Kansas, Montana, Nebraska, New Mexico, North Dakota, Oklahoma, South Dakota, Texas, Utah, Wyoming): https://www.cretaceousatlas.org/geology/

Digital Atlas of Ancient Life Virtual Collection: https://www.digitalatlasofancientlife.org/vc/ (Virtual fossil collection featuring 3D models of fossil specimens sorted by group)

Digital Encyclopedia of Ancient Life: https://www.digitalatlasofancientlife.org/learn/

[email protected]: Quick guide to common fossils: https://earthathome.org/quick-faqs/quick-guide-common-fossils/


Go to the full list of resources about fossils in the south-central U.S.

Go to the full list of general resources about fossils