Mosasaur
Mosasaurs (from Latin "Mosa" meaning the 'Meuse river', and Greek σαύρος "sauros" meaning 'lizard') are an extinct group of large marine reptiles containing 38 genera in total. Their first fossil remains were discovered in a limestone quarry at Maastricht on the Meuse in 1764. Mosasaurs probably evolved from an extinct group of aquatic lizards known as aigialosaurs in the Early Cretaceous. During the last 20 million years of the Cretaceous period (Turonian-Maastrichtian ages), with the extinction of the ichthyosaurs and pliosaurs, mosasaurs became the dominant marine predators. They became extinct as a result of the K-Pg event at the end of the Cretaceous period, about 66 million years ago.
Tylosaurus
Like many other mosasaurs, the early history of this taxon is complex and involves the infamous rivalry between two early American paleontologists, Edward Drinker Cope and Othniel Charles Marsh. Originally, the name ""Macrosaurus" proriger" was proposed by Cope for a fragmentary skull and thirteen vertebrae collected from near Monument Rocks in western Kansas in 1868. It was placed in the collections of the Harvard Museum of Comparative Zoology. Only a year later, Cope redescribed the same material in greater detail and referred it, instead, to the English mosasaur taxon "Liodon". Then, in 1872, Marsh named a more complete specimen as a new genus, "Rhinosaurus" ("nose lizard"), but soon discovered that this name had already been used for a different animal. Cope suggested that "Rhinosaurus" be replaced by yet another new name, "Rhamposaurus" which also proved to be preoccupied. Marsh finally erected "Tylosaurus" later in 1872, to include the original Harvard material as well as additional, more complete specimens which had also been collected from Kansas. A giant specimen of "T. proriger", recovered in 1911 by C. D. Bunker near Wallace, Kansas is one of the largest skeletons of "Tylosaurus" ever found. It is currently on display at the University of Kansas Museum of Natural history.
In 1918, Charles H. Sternberg found a "Tylosaurus", with the remains of a plesiosaur in its stomach. The specimen is currently mounted in the United States National Museum (Smithsonian) and the plesiosaur remains are stored in the collections. Although these important specimens were briefly reported by C. H. Sternberg (1922), the information was lost to science until 2001. This specimen was rediscovered and described by Everhart (2004a). It is the basis for the story line in the 2007 National Geographic IMAX movie "", and a book by the same name (Everhart, 2007).