Reptiles of the class Reptilia are cold-blooded, regulating their body temperature based on environmental conditions. Their thick, scaly skin comprised of keratin, a protein found in human nails, minimizes water loss through evaporation.
Diurnal, or active during the day, lizards are the most widely observable reptile in the preserve. Their varied diet ranges from the horned lizard which feasts on ants to the desert iguana which dines on plants and carrion. Certain lizard species known as "glass snakes" have no functional legs. Lizards have eyelids and ears, which distinguishes them from snakes. In response to stress and other environmental factors, some lizards will change color.
Snakes are the most numerous reptile found within the preserve. They descended from a four-legged terrestrial ancestor, and a few, such as boas, retain skeletal vestiges of hind legs. Lacking eyelids, snakes are unable to blink or close their eyes. A brille or transparent scale acts like a contact lens and serves to protect the eye. All snakes also lack external ear openings and tympanums (eardrums), enabling them to hear only low frequency seismic vibrations. Snakes have unique skulls designed so that they can unhinge their jaws, and swallow prey several times larger than their head. The majority of snakes lay eggs, although some such as the rosy boa, bear live young.