Tyrannosaurs. They're a type of dinosaur - those were a bunch of giant reptiles that used to be around before the last big extinction event...oh, sixty-six million-ish years ago. A meteor hit the earth and most of the life forms died. It took ages after that for anything interesting to happen there again.

There weren't any humans back then, obviously. Nothing as intelligent as a human, either. But humans just love finding dinosaur bones.