One Tyrannosaurus rex seems scary enough. Now picture 2.5 billion of them. That's how many of the fierce dinosaurs probably roamed Earth over the course of a couple million years, a new study finds.
One Tyrannosaurus rex seems scary enough. Now picture 2.5 billion of them. That's how many of the fierce dinosaurs probably roamed Earth over the course of a couple million years, a new study finds.