which era did dinosaurs first appear
Geological timescale. Triassic period: 250â200 million years ago. Jurassic period: 200â145 million years ago. Cretaceous period: 145â65 million years ago. Dinosaurs roamed the planet for about 165 million years, during a time in the Earthâs history called the Mesozoic Era. It is difficult to imagine how long this was, until we compare it with ourselves: humans have lived on Earth for less than two million years. During the Mesozoic Era, the Earthâs landmasses changed dramatically, new seas were formed, and plants and animals evolved.