5.4" Mosasaur (Platecarpus) Rib Section - Kansas

This is a 5.4" long, rib section of a Mosasaur, Platecarpus. It comes from the Late Cretaceous, Smoky Hill Chalk in Gove County, Kansas. There are two repaired cracks through this rib section.



Platecarpus is an extinct aquatic lizard belonging to the mosasaur family. Fossils have been found in the United States as well as a possible specimen in Belgium and Africa. It reached lengths of up to 14 feet long, half of that length being it's tail. Platecarpus probably fed on fish, squid, and ammonites. Like other mosasaurs, it was initially thought to have swum in an eel-like fashion, although a recent study suggests that it swam more like modern sharks.

The Smoky Hill Chalk Member of the Niobrara Chalk formation is a Cretaceous conservation Lagerstätte, or fossil rich geological formation, known primarily for its exceptionally well-preserved marine reptiles. It outcrops in parts of northwest Kansas, its most famous localities for fossils, and in southeastern Nebraska. Large well-known fossils excavated from the Smoky Hill Chalk include marine reptiles such as plesiosaurs, large bony fish such as Xiphactinus, mosasaurs, flying reptiles or pterosaurs (namely Pteranodon), flightless marine birds such as Hesperornis, and turtles. Many of the most well-known specimens of the marine reptiles were collected by dinosaur hunter Charles H. Sternberg and his son George.