There's a new T. rex in town, but this one didn't hunt on land. It ruled the ancient seas.

Scientists have described a new species of mosasaur, a member of a marine reptile group that lived at the same time as dinosaurs during the Cretaceous period (145 million to 66 million years ago). The newly named species fits into an already known genus: Tylosaurus. But its new species name, Tylosaurus rex — T. rex, for short — sets it apart from the other mosasaur species in the group.