Читать книгу The Handy Dinosaur Answer Book - Patricia Barnes-Svarney - Страница 112

Based on the current findings in fossil records, there were not many dinosaurs living during the Triassic period. Dinosaurs began to evolve from the reptiles toward the end of the Triassic period, but great numbers of the creatures did not flourish until the Jurassic period.

What were the first true dinosaurs like?

Based on current fossil finds, the first true dinosaurs emerged in the Late Triassic period, between about 230 to 225 million years ago. They were small, agile, carnivorous reptiles whose unique characteristics, such as two-legged motion, enabled them to quickly dominate the available ecological niches.

Apparently, by the time dinosaurs evolved, they had already split, even at this early stage, into two major groups: the ornithischians and the saurischians. These two main groups of dinosaurs are based historically on their hipbone structure.