Ilustração de Tylosaurus attacks a Styxosaurus in Cetaceous waters.

Tylosaurus attacks a Styxosaurus in Cetaceous waters. Tylosaurus was a North American Mosasaur, a sea reptile related to modern monitor lizards, that hunted the Western Interior Seaway throughout most of the late Cretaceous (89-72 million years ago). Among the largest Mosasaurs it can get as long as 50 feet. Styxosaurus is a long necked plesiosaur that grew up to 50 feet long, with nearly half that length being neck, they were not as heavily built as mosasaurs and would sometimes end up as a Tylosaurs prey.