Scientists theorize that there were a number of reasons for the emergence of dinosaurs in the Late Triassic period. One reason was that dinosaurs evolved to become biologically superior. For example, they developed an erect posture, with bipedal (two-footed) motion. This gave them a longer stride and quickness, enabling them to catch and devour other semi-erect reptiles. Another adaptation might have been warm-bloodedness—although this idea is still controversial. If it is true that the reptiles developed a form of warm-bloodedness, it would have allowed them to be more active than their cold-blooded relatives.

Still other scientists suggest that these adaptations were not the reason for the dominance of dinosaurs. Instead, they believe a major extinction of certain therapsids (reptilian ancestors of mammals), rhynchosaurs (lizard-like reptiles), and early archosaurs (reptiles comprising dinosaurs, pterosaurs, and crocodilians) in the middle of the Triassic period opened up ecological niches that the dinosaurs then filled.