Final Review Question 21

Q: Does a mesotarsal ankle provide us with enough evidence to determine
whether an archosaur with a mesotarsal ankle could be quadrapedal or
bipedal?  Since it's an evolutionary trait for dinosaurs, and some
dinosaurs were quadrapedal and others were bipedal, does that mean a
Marasuchus, who had a mesotarsal ankle, could have been either?

A:  Good Point!  The question relating to this is misleading.  The question is supposed to be about the ankle joint telling us that marasuchus-like archosaurs are very closely related to dinosaurs, and therefore, since marasuchus-like dinos are all bipedal, the first dinosaurs are also thought to be bipedal.   This is also supported by the earliest known saurischians and ornithischians all being bipedal.