By Matthew Richardson and Amber Settle (1999)
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In this photographic atlas the head skeleton of a cat (Felis) and an alligator (Alligator mississippiensis) are examined. One of the most noticeable areas of evolutionary development is in the area of the skull and jaw. Major trends in the development of the bones composing the head skeleton in the different groups of vertebrates accompany milestones in evolutionary development such as the transition from a totally aquatic existence to that of a semi-terrestrial animal, the development of a totally terrestrial vertebrate (reptiles) from amphibians, and then the rise of energy-expensive endothermic animals (mammals/birds). Each of these transitions required special adaptations of the animals which represent them. For the most part, adaptations accounted for the forces of gravity experienced on land that were not present in aquatic environments, and for the need to meet the high metabolic needs of endothermic animals. Noticeable trends in the bone composition of the head skeleton will now be briefly addressed. Specific examples will be limited to the two specimens represented in this atlas.
Trends in the Development of the Head Skeleton