Final answer:
The correct option is D). Reptiles with two temporal fenestrae on each side of the skull are known as diapsids. This group includes dinosaurs, birds, and most living reptiles. The distinction of skull types based on temporal fenestrae is significant for understanding reptilian evolution and classification.
Step-by-step explanation:
Reptiles with two temporal fenestrae on each side of the skull are diapsids. The different skull types among amniotes primarily include the anapsid skull, the synapsid skull, and the diapsid skull. Temporal fenestrae are skull openings that facilitate the attachment and expansion of jaw muscles, which are important for feeding and, in some cases, ventilation of the lungs. Anapsids, such as traditional interpretations of turtles, have no openings, synapsids, which include mammals, have one opening, and diapsids have two openings. Examples of diapsids include dinosaurs, birds, and reptiles like lizards and snakes.
The Evolution of Amniotes shows that the early amniotes diverged into two main lines: synapsids and sauropsids, with the latter splitting into anapsids and diapsids. The diapsid lineage gave rise to most modern reptiles. While members of the order Testudines (turtles) have an anapsid-like skull, molecular studies indicate a diapsid ancestor, which suggests secondary loss of temporal fenestrae in their evolution. This evolutionary phenomenon is an example of how characteristics can change or revert in a lineage.