Write about how this seemingly simple change can lead to large divisions between the species of dinosaurs and allow for evolution from a single species. Look at the signs/displays to see other traits that separated groups of dinosaurs and help to show evolution in the groups. Also, note that a single lineage of dinosaurs did survive- and evolve into a totally different species. Which dinosaur was this, and how is it extant today? Think about the evolutionary steps needed to separate a flying, endothermic avian from scaled, running reptiles. What evidence did they give for this transition?