The Triassic Period, in geologic time, the first period of the Mesozoic Era. It began 252 million years ago and ended 201 million years ago. It was an era of changes. A lot of happened to Earth and its life-forms. The first dinosaurs appeared during the Triassic Period. Carnivorous mammal-like reptiles called cyodonts evolved. There were also many kinds of aquatic reptile, including tortoise and turtles. Palm-like cycads grew in the Triassic Period.