The ‘common ancestor of reptiles and birds’ is way older than dinosaurs. And it’s also the common ancestor of all mammals. You could get the common ancestor of

The ‘common ancestor of reptiles and birds’ is way older than dinosaurs. And it’s also the common ancestor of all mammals. You could get the common ancestor of birds, dinosaurs, and a living reptile if you just go to the common ancestor of, say, a chicken and a crocodile. That’s also the ancestor of pterosaurs as well as dinosaurs though.