Archosaurs were a whole group of reptiles that appeared during the Triassic Period. Most of them were predators, and they gave rise to animals such as the dinosaurs, the crocodiles and their relatives, and the flying pterosaurs. The archosaurs were the group of animals in which the modification to the hips and legs developed. This modification led to the dinosaurs being able to support their own weight and to stand upright. Because they were able to move more efficiently and most were fierce predators, it is thought that they may have killed off the mammal-like reptiles and other early relatives.
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