Tylosaurus

Tylosaurus was a ferocious marine lizard that powered itself through the water with sweeping motions of its long body and fish-like tail. At a massive 46 ft long, it was about the size of a humpback whale and one of the largest mosasaurs. It lived in the Western Interior Seaway of North America during the Late Cretaceous, from about 75 to 85 million years ago.