Final answer:
The three major groups of amniote skulls are anapsid, synapsid, and diapsid, characterized by having no temporal openings, one opening, and two openings, respectively. Anapsids are seen in some early amniotes and turtles; synapsids led to mammals, and diapsids evolved into reptiles, including birds and dinosaurs.
Step-by-step explanation:
The Three Major Groups of Amniote Skulls
The amniotes are a group of animals distinguished from amphibians by their adaptive features for terrestrial life, including the presence of a shelled egg containing amniotic membranes. These amniotic membranes allow the embryo to develop in a watery environment within the egg, which facilitates greater independence from aquatic environments. Moreover, the amniotes exhibit diversity in their skull structures, which are classified into three major groups based on the presence and number of temporal fenestrae, openings in the skull behind the eyes. These groups are the anapsids, synapsids, and diapsids.
Anapsid skulls are characterized by having no temporal openings. This structure is associated with some of the very early amniotes and modern turtles. Synapsid skulls have a single temporal opening and gave rise to mammals. Finally, diapsid skulls feature two temporal openings and led to the evolution of reptiles, including birds and dinosaurs.
These skull structures reflect evolutionary relationships among amniotes. About 320 million years ago, early amniotes diverged into two major lineages: synapsids and sauropsids. Synapsids are the predecessors of modern mammals, while sauropsids evolved into reptiles and birds. Evolutionarily, the most common classification of amniotes was into the classes Mammalia, Reptilia, and Aves, although this does not accurately reflect the phylogenetic relationships due to birds descending from dinosaurs, which were diapsids.