Initially all were waddling quadrupeds. Bipedalism and hostility of Permian-Triassic period was to later become the reason that would make a group of vertebrates, the dinosaurs, to dominate earth. read more
This is why: There were plant- and animal-eating bipedal dinosaurs, but practically no carnivorous quadruped dinosaurs.* Most quadrupedal dinosaurs had much larger rear legs than front legs (unlike non-dinosaur reptile and mammal quadrupeds, that generally have front and rear legs of similar size). read more
Many early relatives of dinosaurs and crocodilians were all bipedal and looked very similar, with one of the biggest differences being the ankle joint. What is definitely true is that the ancestors of pterosaurs and dinosaurs were bipedal, and the very first dinosaurs were definitely also bipeds. read more
The Triassic bipeds became dinosaurs. After the previous extinction, available space was incredible and rents were low. The dinosaurs poised with their supremacy spread out like weedy opportunists. Surviving Triassic and becoming masters of the Mesozoic era, the bipedal predators diversified during the Jurrasic era. read more