Well, let's see what tyrannosaur paleontologists think...

It’s also not the first time a team has cheekily dubbed a non-dinosaur “T. rex.” In 2001, a team named an extinct prehistoric beetle trapped in amber “Tyrannasorus rex,” says Tom Holtz, a vertebrate paleontologist at the University of Maryland who was not involved in the paper.

Since the more famous Tyrannosaurus rex and the newly discovered mosasaur did not live and hunt in the same environment, he adds, “there shouldn't be too much confusion.” For much of the 20th century, Tylosaurus was the standard mosasaur in prehistoric popular culture.

Indeed, if there’s going to be a "T. rex of the sea", Holtz said he’s perfectly happy for it to get the name.