When dinosaurs appeared on the scene, the land was inhabited by several species of archosaurs and therapsids such as ethosaurs, synodonts, disinodonts, and ornithozogides.
Most of these other animals became extinct in the Triassic in one of two extinction incidents. The first was between the time Cadmium and Thorium about 215 million years ago, when dicynodonts and a variety of argosouromorphs became extinct.
This was followed by the Triassic-Jurassic extinction about 200 million years ago, which marked the end for most of the other groups of early archosaurs such as the ethosaurs, ornithozoegides and phytosauruses.
These losses resulted in the land being dominated by crocodile-likes, dinosaurs, mammals, pterosaurs and turtles.
