Illustration of a herd of Coelophysis sp. dinosaurs surrounding a phytosaur reptile. Coelophysis was one of the earliest true dinosaurs, appearing in what is now North America in the late Triassic period (between around 220 and 210 million years ago). It was a fast bipedal (two-legged) predator and scavenger that reached around three metres in length, but stood less than a metre tall at the hips. Phytosaurs were semi-aquatic reptiles that also lived during the late Triassic and resembled modern crocodilians. A Hesperosuchus agilis crocodylomorph is on the fallen branch in the foreground.