Hall of Saurischian Dinosaurs April 9, 2010

The earliest-known dinosaurs appeared about 228 million years ago; their fossils have been found on every continent. They dominated the land until about 65 million years ago, when an episode of extinction eliminated the non-avian dinosaurs (but not the birds) as well as many other animals and plants, both on the land and in the seas. Possible causes for these extinctions include the impact of an extraterrestrial object or a major, global peak in volcanic activity.