Reptiles - Dinosaurs

This successful Diapsid (Dinosaurs) group, made up mainly of land-dwelling reptiles, first appeared about 225 million years ago, having evolved from the closely related thecodontian archosaurs ( ancestors of the dinosaurs). They are divided into two orders: the reptile-hipped Saurischia, in which the pubic bone faces forwards; and the bird-hipped Ornithischa, in which it faces backwards. Included in the Saurischia are the great four-footed herbivores and the two-footed flesh-eaters, while the Ornithischia contains the remaining planet-eaters. The rise to dominance of the dinosaurs has been attributed to modifications of the limbs and girdle bones, which so improved their stance and gait that they were able to adapt to new habitats. Their largely unexplained extinction at the end of the Mesozoic Era, along with most of the great aquatic reptiles, brought to an end 150 million years of domination.