Chapter 25, Problem 15PIAT

Redraw the tree in question 11 as a cladogram (i.e., with branch lengths not pinned to time scale). For simplicity, show only the branches with animal icons. Then (1) add an outgroup to the theropods called the Sauropoda (which includes the enormous Apatosaurus); (2) mark the origin of downy feathers, which occur in all theropods; and (3) mark the origin of shafted feathers and wings, which occur in all the groups except Tyrannosauroidea. Can the presence of feathers and wings be considered a synapomorphy that triggered the adaptive radiation of birds? Why or why not?