Amniotes are divided into three groups based in their skull morphologies. what are these three groups, and how do their skulls differ? which living amniotes, if any, originated from each of these three groups?

Based on skull morphology, amniotes can be divided:

1. Anapsids-It is a group of organisms with skulls that lack openings called temporal fenestrae. Turtles are an example of Anapsids.

2. Diapsids-It is a group of organisms with skulls that have two temporal fenestrae behind the orbit, one superior and one inferior. Examples are crocodilians, birds, tuataras, lizards and snakes.

3. Synapsids-It is a group of organisms that have one temporal fenestra behind the eye. The example is mammals.