Tylosaurus

Tylosaurus (Greek τυλος/tylos 'protuberance, knob' + Greek σαυρος/sauros 'lizard') was a mosasaur, a large, predatory marine reptile closely related to modern monitor lizards and to snakes, from the Late Cretaceous. A distinguishing characteristic of Tylosaurus is its elongated, cylindrical premaxilla (snout) from which it takes its name. Unlike other mosasaurs, Tylosaurus did not have teeth all the way forward on its premaxilla, as the bony protuberance was free of teeth. Tylosaurus also have 24 to 26 teeth in the upper jaw, 20 to 22 teeth on the palate, 26 teeth on the lower jaw, 29 to 30 vertebrate between the skull and hip, 6 to 7 vertebrae in the hip, 33 to 34 vertebrae in the tail with chevrons, and a further 56 to 58 vertebrae making up the tip of the tail. Early restorations showing Tylosaurus with a dorsal crest were based on misidentified tracheal cartilage, but when the error was discovered, depicting mosasaurs with such crests was already a trend. Its skin had many small scales. Along with plesiosaurs, sharks, fish, and other mosasaurs, Tylosaurus was a dominant predator of the Western Interior Seaway during the Late Cretaceous. The genus was among the largest of the mosasaurs (along with Mosasaurus hoffmannii), with the possibly conspecific Hainosaurus bernardi reaching lengths up to 12.2 meters (40 ft), and T. pembinensis reaching comparable sizes. T. proriger, the largest species of Tylosaurus, reached lengths of about 14 m (46 ft). 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 Sea Monsters: A Prehistoric Adventure, and a book by the same name (Everhart, 2007). A photograph of a Tylosaurus skull was taken by George F. Sternberg about 1926 after he collected and prepared the specimen. It was discovered in the Smoky Hill Chalk of Logan County, Kansas. Sternberg offered the specimen to the Smithsonian and included a photograph in his letter to Charles Gilmore. Copies of the original photos are in the archives of the Sternberg Museum of Natural History (FHSM). The specimen is FHSM VP-3, the exhibit specimen in the same museum. A 34 feet (10 m) long Tylosaurus found in Kansas by Alan Komrosky in 2009 is now on display at the Museum of World Treasures in Wichita, Kansas.