Birds, snakes, lizards, turtles, and crocodiles are all thought to share a common ancestor and several homologous traits. Assuming that this is true, these groups of animals and their common ancestor would represent

Monophyletic groups

Explanation:

Animals in monophyletic groups comprises of jaw vertebrates (typically known as a group of gnathostomes). They are monophyletic because all of the  descendants of the most recent common ancestor are include in the group. The group can be defined by the shared derived feature such as jaw. This shared derived feature of jaw is known as synapomorphy. This derived feature of jaw is significant since the ancestral state were plesiomorphy ( a jawless condition). Other factor of monophyletic groups include the presences of bone.

allowed for the prediction of the properties of missing elements.