ZOOL 403 Study Guide - Final Guide: Cranial Kinesis, Squamata, Anapsid
9 May 2020
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Document Summary
Members of the lepidosauromorpha and archosauromorpha have in common several characters that are evident externally. The most obvious trait is the possession of epidermal keratinized structures known as scales. This thickened layer of keratin acts as a barrier that prevents moisture loss to the atmosphere, thus allowing individuals to occupy dry, terrestrial environments for prolonged periods of time without excessive water loss. In turtles, crocodilians and some lizards, the scales are associated with bony plates (osteoderms) in the dermal layer that provide protection from predators. Another integumentary structure, claws, make their first appearance in these vertebrates. These hard, keratinous cone-like sheaths encase the terminal phalanges of the digits. Diapsid head skeletons exhibit a number of shapes and structural differences that are useful for classifying major groups. The most obvious variation is apparent in the pattern of fenestration in the temporal region of the skull. The primitive condition in amniotes is a temporal region that is not pierced by openings.
