Dinosaurs' Rise to Dominance Was Gradual

Skeletal reconstruction of dinosaur precursors and dinosaurs from the Hayden Quarry. The small animal in the lower left foreground is Dromomeron romeri, and the four-legged creature behind it is a Silesaurus-like animal. Dinosaurs include Chindesaurus bryansmalli (to the right, second from the back) and a Coelophysis-like theropod (animal in the far back). Credit: Science