The earliest Prehistoric animals to live were jawless, spineless creatures that roamed the oceans about 540 million years ago. It wasn’t until the Devonian period, 400 million years ago, when the prehistoric creatures grew legs and left the ocean, these are the prehistoric ancestors to all vertebrate creatures on earth today. Once on land, the prehistoric creatures underwent a bunch of different adaptations for running, crawling, flying, and jumping; it was then when the rise of the dinosaurs took place, in the Triassic period about 230 million years ago. Even though the dinosaurs ruled, many small, rodent-like mammals were alive and these small mammals, along with some birds, amphibians, and reptiles survived the mass extinction that wiped out the dinosaurs. Although 90% of the species that have lived on Earth throughout its existence are extinct, most of the creatures that survived this first mass extinction still exist today.