Final answer:
Anapsids lack temporal fenestrae, synapsids have one, and diapsids have two. Turtles are classified as diapsids, mammals are synapsids, and birds and reptiles are diapsids. These skull structures aided the rise of reptiles as dominant land vertebrates.
Step-by-step explanation:
The anatomical differences between anapsid, synapsid, and diapsid skulls lie in the number of temporal fenestrae, which are openings behind the eyes in the skulls of amniotes. Anapsids have no openings, synapsids have one opening, and diapsids have two openings. Living members that exhibit these patterns include turtles (traditionally thought to be anapsids based on skull structure, but now considered diapsids due to genetic evidence), mammals for synapsids (as this group includes the lineage that led to mammals), and birds and reptiles for diapsids.
Reptiles are distinguished by features such as scaly skin, a terrestrially adapted egg protected by amniotic membranes, and the evolution of rib ventilation of the lungs, which allowed them to become the dominant land vertebrates, replacing amphibians with these adaptations. The evolution of reptiles dates back to approximately 340 million years ago, with an early divergence into the synapsid and sauropsid lineages, the latter further splitting into anapsids and diapsids.