What is the Evolutionary History of Dinosaurs?
Dinosaurs evolved about 230 million years ago, splitting from their archosaur cousins in the early Triassic, 21 million years after the catastrophic Permian-Triassic extinction, which wiped out most life on Earth. Like other archosaurs, dinosaurs are characterized by socket-teeth, which makes them less likely to be pulled loose during feeding, distinctive holes in the skull, and a special ridge for attaching muscles on the femur. Prior to the Permian-Triassic extinction, archosaurs were a relatively obscure group of reptiles. In the late Permian, the land was dominated by the therapsids, ancient relatives of mammals. Most therapsids didn’t survive the end-Permian extinction very well, or the arid world which followed it. This left several major ecological niches wide open, which the archosaurs began to exploit. Many scientists believe that reason for the rise of archosaurs and dinosaurs had to do with better strategies to cope with arid environments. For instance, archosaurs can releas
