Dinosaurs were an order of reptiles which existed from about 230 million years ago (MYA) to 65 MYA. Dinosurs varied in size drastically from the 3 foot long Eoraptor lunensis to the 90 foot long Diplodocus. At the end of the Cretaceous period, 65 MYA, a catastrophic mass-extinction event took place. This is commonly thought to have been an asteroid or massive volcanic event. One significant group of dinosaurs has survived until the present day; scientests consider modern birds to be the direct descendants of theropod dinosaurs.