Size and Weight:
The 35-foot-long, seven-ton Tylosaurus was about as well-adapted to terrorizing sea creatures as any marine reptile could be, sporting a narrow, hydrodynamic body, a blunt, powerful head suited to ramming prey, agile flippers and a maneuverable fin on the end of its long tail. This late Cretaceous creature was one of the largest of all mosasaurs--the family of aquatic reptiles that succeeded the ichthyosaurs, pliosaurs and plesiosaurs of the earlier Mesozoic Era and are distantly related to modern snakes and monitor lizards.
Like one of those plesiosaurs, Elasmosaurus, Tylosaurus figured in the famous 19th-century feud between the famous paleontologists Othniel C. Marsh and Edward Drinker Cope (commonly known as the "Bone Wars.") Squabbling over a set of incomplete Tylosaurus fossils, Marsh suggested the name Rhinosaurus ("nose lizard," a great missed opportunity if ever there was one) while Cope touted Rhamposaurus instead. It was left to a third famous paleontologist, Charles Sternberg, to make the most dazzling Tylosaurus discovery of all, a specimen with the fossilized remains of an unidentified plesiosaur in its stomach.