Reptilia is a class of animals which includes (among other things) tortoises and turtles, crocodilians, snakes, and lizards. It may surprise many people to learn that birds are closely related to reptiles; in fact, birds are more closely related to crocodilians than to any other living group. However, birds are so morphologically and physiologically unique from the members of Reptilia that they are grouped within their own class (Aves).
Reptiles inhabit a wide variety of habitats and may be herbivores (plant-eaters), insectivores (insect-eaters), pescivores (fish-eaters), carnivores (meat-eaters), or scavengers (carrion-eaters). There are no pescivorous reptiles in the Preserve for the obvious reason, but all other types are represented. All reptiles possess a thick scaly skin comprised of keratin, a type of protein found in the nails of humans. The thick skin helps to minimize water loss through evaporation. All living reptiles are also ectothermic, poikilothermic, and bradymetabolic, a suite of terms which define a condition that was once inaccurately named "cold-blooded." Ectothermic organisms regulate their body temperatures externally by utilizing environmental conditions to raise or lower their body temperature as needed. Organisms that maintain a widely variant body temperature which usually approximates variations in the ambient temperature are termed poikilotherms. Resting metabolism, the amount of internal activity (such as cellular respiration) in an animal when that animal is at rest, may be described as either high or low. Bradymetabolic organisms such as reptiles have low resting metabolisms. (For a description of the converse of these conditions refer to the section on mammals.)
Over 8,000 species of reptiles have been documented worldwide, approximately 340 species of which may be found in North America. Of these, 38 species have been described for Mojave National Preserve. Lizards are among the most often spotted of desert wildlife, with most lizard species being highly active during the day. Eighteen species representing eight families are known from the Preserve. Many people believe that the presence of legs distinguishes lizards from snakes, but in fact, some of the lizards in the family Anguidae, most of which reside in North and South America, are legless lizards. However, since there are no species of legless lizards within the Preserve, the presence or absence of legs may be used to differentiate the two groups. Several other traits also identify lizards, among them multiple rows of belly scales (snakes have only one row), and skin that is shed in patches (snakes generally shed their skins all in one piece). The feeding habits of lizards range from strict, such as the herbiverous western chuckwalla (Sauromalus obesus) and the ant-eating horned lizard (Sceloporus platyrhinos) to highly opportunistic, such as the plant, insect, and carrion-eating desert iguana (Dipsosaurus dorsalis).
Snakes are the most numerous reptile (in terms of species) with 19 species from five families described within the Preserve. Although modern snakes lack limbs they descended from a four-legged terrestrial ancestor, and a few, such as boas, retain skeletal vestiges of hind legs. All snakes lack eyelids and are therefore unable to blink or close them. Instead, a transparent scale called a brille acts like a contact lens and serves to protect the eye. All snakes also lack external ear openings and tympanums ("eardrums"). Consequently, they are only able to hear low-frequency seismic vibrations (sounds which are transmitted through the ground) and are not able to hear high-frequency air-borne sounds. Snakes have unique skulls and can "unhinge" their jaws, allowing a snake to swallow prey that is several times larger than its head. The elongation of internal organs is necessitated by the long and slender shape of the body, and the left lung is absent or reduced in size. Snakes also use their tongue to smell, sampling particles from the air and transporting them to the highly sensitive Jacobson's organ located on the roof of the mouth. The majority of snakes are oviparous, that is, they lay eggs. However, some species are viviparous ("live-bearing"), including the rosy boa (Lichanura trivigata). There are also three venomous species of snake known from Preserve. These species are pit vipers and have heat-sensing organs on the face to aid in detecting prey. (Boas also have sensing pits on their face.) Interestingly, a rattlesnake is born with just one rattle segment, and one segment is added each time the snake sheds, as parts of the old skin are trapped by a constriction at the end of the tail.
The desert tortoise (Gopherus agassizii) is the most famous of all Mojave Desert reptiles. Tortoises belong to the order Testudines, a group which also includes turtles, sea turtles, and terrapins. The members of this group have a shell which completely encases the body, making them immediately identifiable. Testudines also have no teeth in their jaws. Tortoises are unique from other Testudines in that they spend no part of their life cycles in the water. The desert tortoise is listed as threatened under the Endangered Species Act.
