When dinosaurs appeared, terrestrial habitats were occupied by various types of basal archosaurs and therapsids, such as aetosaurs, cynodonts, dicynodonts, ornithosuchids, rauisuchias, and rhynchosaurs.
Most of these other animals became extinct in the Triassic, in one of two events.
First, at about the boundary between the Carnian and Norian faunal stages , dicynodonts and a variety of basal archosauromorphs, including the prolacertiforms and rhynchosaurs, became extinct.
This was followed by the Triassic-Jurassic extinction event , that saw the end of most of the other groups of early archosaurs, like aetosaurs, ornithosuchids, phytosaurs, and rauisuchians.
These losses left behind a land fauna of crocodylomorphs, dinosaurs, mammals, pterosaurians, and turtles.
