‘That’s a lot of teeth’: 2.5 billion T rex walked the earth, researchers find

Experts calculate the total number of the dinosaurs that lived over 127,000 generations

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

Using calculations based on body size, sexual maturity and the creatures' energy needs, a team at the University of California, Berkeley, figured out just how many T rex lived over 127,000 generations, according to a study in the journal Science on Thursday. It's a first-of-its-kind number, but just an estimate with a margin of error that is the size of a T rex.