Explore our collection of all prehistoric creatures! Most are dinosaurs, but we also have some pterosaurs, early proto-mammals, and extinct marine reptiles in the mix as well. There are roughly 700 known species of extinct dinosaurs, and fossils have been found on all seven continents. They lived on Earth for about 245 million years, and non-avian dinosaurs went extinct about 66 million years ago. Modern birds share a common ancestor with non-avian dinosaurs.