Dinosaur Periods By markmarshall Jun 28, 2000 Permain Period. 286 million years ago. The first sail back reptile appeared. Period: Jun 28, 2000 to Jun 28, 2010 timespan Jun 28, 2002 Triassic Period.245 million years ago. First dinosaurs, mammals, and frogs appeared. Jun 28, 2003 Jurassic Period. 208 million years ago. First birds. Jun 28, 2005 Cretacious Period. 144 million years ago. Dinosaurs died out. First snakes and modern mammals appeared.