At the Royal Ontario Museum’s exhibit on “Feathered Dinosaurs” we weren’t allowed to make drawings nor take photographs of the exhibits , but I did take notes, on which I base this diagram. I am no scientist and any mistakes or misinterpretations are mine, but this is how it looked to me.
- Testudina = anapsids, possibly including Testudines. Maybe this should be “Anapsids = Anapsids, possibly including Testudines.” It’s unknown whether turtles and their relatives are basally anapsid or developed the trait secondarily.
- Pterosaurs = flying reptiles
- Ornithischia = bird-hipped, plant-eating dinosaurs
- Saurischia = dinosaurs with gizzard stones
- Sauropodomorpha = long-necked, plant-eating dinosaurs
- Theropoda = bipedal dinosaurs, predatory, with wishbones, possibly feathered
- Allosauroidea = allosaurs; hollow bones. All have wishbones
- Coelurosauria = tyrannosaurs, Oviraptor, Velociraptor, & birds
- Ornithomimosauria = ostrich-like dinosaurs
- Pygostylia = birds with reduced stump of tail
- Palaeognathae = rheas, emus, cassowaries et al.
- Neognathae = more modern birds
As the exhibit progressed, various characteristics such as backward-pointing toes, ankle bone bracing the shin, hollow bones, fewer teeth, beaks, and, of course, feathers appeared and became more prominent.
On the Tree of Life Web site you can see a cladistic diagram for the group Aves.