Final answer:
The model diapsid animal is the lizard, which retains the classical diapsid skull structure. Turtles, though descending from diapsid ancestors, exhibit an anapsid-like skull, which could be due to evolutionary loss of traits. These examples demonstrate the complexity of evolutionary processes and the integration of morphological and molecular data in understanding phylogeny.
Step-by-step explanation:
The animal from the lab considered a "model" diapsid, meaning it still displays both post-orbital fenestra, is c) Lizard. Diapsid reptiles are characterized by two pairs of temporal openings in their skull. Crocodiles, birds, snakes, and lizards are all considered diapsids, but when it comes to retaining the classical diapsid skull structure with both pairs of temporal fenestrae, lizards are often taken as the model example. Despite being in the same diapsid group, snakes have evolved a more derived skull structure due to their specialized lifestyle.
As for turtles, this is indeed a fascinating subject. While members of the order Testudines, which includes turtles, possess an anapsid-like skull without obvious temporal fenestrae, molecular studies suggest that they descended from diapsid ancestors. This apparent discrepancy may be explained by evolutionary processes such as secondary loss, where a species loses a trait that its ancestors possessed. In the case of turtles, this could mean that over time and through evolution, the temporal fenestrae that are typically seen in diapsids were lost, giving them their current anapsid-like appearance. This example highlights the dynamic nature of evolutionary changes and the importance of both morphological and molecular data in reconstructing phylogenetic relationships.