The extinction of the dinosaurs event, or more generally the CretaceousTertiary extinction event, occurred approximately 65.5 million years ago. It was a large-scale mass extinction of animal and plant species in a geologically short period of time. It is usually associated with a thin band of sedimentation found in various parts of the world. Dinosaurs, or "terrible lizards", were the dominant terrestrial vertebrateanimals for over 160 million years, from the late Triassic period (about 230 million years ago) until the end of the Cretaceous period (about 65 million years ago), when the CretaceousTertiary extinction event caused the extinction of most dinosaur species. The fossil record indicates that birds evolved from the ropod dinosaurs during the Jurassic period. Paleontologists have identified over 500 distinct genera and more than 1000 different species of dinosaur, and remains have been found on every continent on Earth.