Tylosaurus, whose name means “knobbed lizard”, is a long-lived genus of several long-snouted mosasaurs which ruled the shallow late Cretaceous seas from the Cenomanian to the Maastrichtian stages of the Late Cretaceous, around 92-66 million years ago. The many species of Tylosaurus varied greatly in size, ranging from the small 7-meter-long Tylosaurus nepaeolicus to the giant 13-meter-long or school bus-sized Tylosaurus proriger (shown here), which had a skull length of 1.4-1.5 meters long and preyed upon the large fish, plesiosaurs, turtles and smaller mosasaurs of the Western Interior Seaway alongside the local species of Mosasaurus, and some of them have also been found in the tropical seas surrounding the European archipelago alongside Mosasaurus hoffmani. Moreover, some species of this mosasaur have also evolved unique adaptations for thriving in colder waters to the north of their cosmopolitan range. While the larger species of Tylosaurus were formidable apex predators which would have likely used their snouts to ram into the flanks of their large prey in order to stun them, the smaller species might have more often fed on smaller fish or turtles, and fossil evidence of bite marks found on the snouts of some skulls from this mosasaur have also shown that large individuals of Tylosaurus were highly aggressive or even cannibalistic towards smaller members of their own kind and could have engaged in infraspecific combat, possibly with adult males fighting each other over hunting grounds or mates. Until the release of the 2015 film Jurassic World cemented Mosasaurus to mainstream popularity, this genus was the archetypal mosasaur in educational or non-educational works featuring dinosaurs and other prehistoric life, appearing in a wide variety of media ranging from a book featuring Tarzan and pulp-fiction novels to documentaries such as Sea Monsters: A Walking with Dinosaurs Trilogy and Sea Monsters: A Prehistoric Adventure, albeit without the fork tail that it possessed in life, both of which feature Tylosaurus proriger swimming about in its Niobrara Formation environment alongside Hesperornis, Xiphactinus, an Elasmosaurid with Elasmosaurus in the former and Styxosaurus in the latter, a Protostegid turtle with Archelon in the former and Protostega in the latter, and a few small mosasaurs and sharks. One particular T.proriger specimen found from this area in 1917 by Sternberg and his sons also has the remains of a small plesiosaur preserved in its stomach.
