Luck gave dinosaurs their edge

A montage of the skulls of several crurotarsan archosaurs, the "crocodile-line" archosaurs that were the main competitors of dinosaurs during the Late Triassic period (230-200 million years ago). Dinosaurs and crurotarsans shared many of the same ecological niches, and some crurotarsans looked remarkably similar to dinosaurs. However, by the end of the Triassic period most crurotarsans were extinct, save for a few lineages of crocodiles, while dinosaurs weathered the storm and began a 135-million-year reign of dominance. Top (l-r): The rauisuchians Batrachotomus and Postosuchus; middle: the phytosaur Nicrosaurus and the aetosaur Aetosaurus; bottom: the poposauroid Lotosaurus and the ornithosuchid Riojasuchus. Credit: Steve Brusatte