The Age of Dinosaurs began about 250 million years ago. In the beginning they were quite small but over time they evolved into the varied and fascinating creatures that captivate our imaginations today. What we know about dinosaurs is evolving, too We've learned that some dinosaurs were good parents, that dinosaurs could grow new teeth when old ones fell out, and that most dinosaurs walked on two legs. We've even discovered that birds are modern relatives of dinosaurs