Tylosaurus

Kansas designated Tylosaurus kansasensis as its official state marine fossil in 2014, alongside a separate state flying fossil. The species name honors Kansas directly. Its type specimens were found in the Kansas Niobrara Chalk, and the formal species description was published in 2005 based on material from Logan County.

Tylosaurus was a mosasaur, a group of large marine lizards closely related to modern monitor lizards and snakes. It was the largest predator in the Western Interior Seaway, the shallow inland sea that split North America in two during the Late Cretaceous.

Tylosaurus kansasensis reached up to 45 feet in length, making it one of the largest mosasaurs known. It had a long, streamlined body, four paddle-like limbs, and a powerful tail flattened from side to side for propulsion. Its most distinctive feature was a rounded, toothless projection at the tip of its snout, the tylus, which may have been used to ram and stun prey.

The jaws were lined with two rows of teeth on the palate in addition to the outer teeth, giving Tylosaurus a grip that made escape unlikely. Its diet included fish, sharks, smaller mosasaurs, and possibly diving birds like Hesperornis, which shared the same sea. Stomach contents from related specimens confirm it swallowed prey whole or in large pieces.

Tylosaurus was not a dinosaur or a whale but a reptile, the largest of a group that conquered the Cretaceous oceans. It went extinct 66 million years ago at the end-Cretaceous event that also killed the non-avian dinosaurs.

The first Tylosaurus fossils from Kansas were collected in the 1860s and 1870s, when Edward Drinker Cope and O.C. Marsh sent teams into the Niobrara Chalk during the Bone Wars. Cope described the genus Tylosaurus in 1872 from Kansas material, though the species kansasensis was not formally defined until Kansas paleontologist Michael Everhart described it in 2005.

Kansas designated Tylosaurus kansasensis as its state marine fossil in 2014. The choice reflected the species' direct ties to Kansas. Its name, type locality, and most known specimens all come from the state's Niobrara Chalk beds.

The Niobrara Chalk of western Kansas is the type locality for Tylosaurus kansasensis. Logan County, in the northwest part of the state, has produced the type specimen and numerous additional individuals. The chalk outcrops in Logan, Gove, Trego, and neighboring counties are the core of the Kansas mosasaur fossil zone.

Monument Rocks in Gove County is the most famous surface exposure of the Niobrara Chalk. Tylosaurus bones, along with fish skeletons, shark teeth, and the remains of other marine reptiles, erode from these chalk formations and from stream cuts and hillside exposures across the western Kansas plains.

The Sternberg Museum of Natural History in Hays holds multiple Tylosaurus specimens from Kansas, including articulated skeletons. The museum's collection documents more than a century of chalk-bed collecting and provides the primary reference for Kansas mosasaur research.