Found within 75 million year old rock among the Book Cliffs – near Green River, Utah – the tyrannosaur is only represented by part of a hindlimb. That’s not very much to go on, but as paleontologists Tracy Thomson, Randall Irmis, and Mark Loewen suggest in an in-press Cretaceous Research paper, the anatomy and location of those petrified pieces may provide important clues about a major evolutionary pattern among North America’s Cretaceous dinosaurs.

If you were able to take a road trip from New Mexico to Alberta, Canada around 75 million years ago, the communities of dinosaurs you’d pass along the way would change as you drove north. The dinosaurs in the ancient southwest would belong to different genera and species