Drepanosaurs, Tanystropheids, Vancleavea
At right is a hypothesis of evolutionary relationships of the reptile groups found throughout the rock strata at Petrified Forest. These cladograms are the result of analyses that compare anatomical structures in the skeletons of modern and extinct organisms. In other words, the more closely related two animals are, the more they tend to look like one another.
Take a closer look at one of the main reptile groups found at Petrified Forest. Most of what we find at the park are members of Archosauria, or "ruling reptiles." Archosauria is the group to which birds and crocodylians (and their fossil ancestors) belong. When we find archosaur fossils in the field, we can usually tell if they fall along the Ornithodiran (bird-line) or Pseudosuchian (crocodylian-line) lineages by their ankle structure. Pseudosuchians have ankle bones that move against each other, while ornithodirans have ankle bones that stay stationary but rotate over the top of the foot. You might have heard that evolutionarily speaking, birds are reptiles! It's true, birds are not only reptiles but are the only surviving dinosaurs.
Of course, Petrified Forest's fossil record represents a complete ecosystem that supported life beyond only the reptile groups.
Last updated: April 19, 2016