The desert iguana is a large lizard, indeed the largest lizard in the Mojave Desert. Known by its scientific name, Dipsosaurus dorsalis, the desert iguana is one of the most common lizards of the Sonoran and Mojave deserts of the southwestern United States and northwestern Mexico. They also occur on several Gulf of California islands.
First described in the Catalog of North American Reptiles, by Spencer Fullerton Baird and Charles Frédéric Girard, in 1859 as Crotaphytus dorsalis, the desert iguana was reclassified two years later as Dipsosaurus dorsalis by Edward Hallowell. The generic name comes from a combination of two Greek words meaning “hungry lizard.: “Dipsa” (δίψα) for “thirsty” and “sauros” (σαῦρος) for “lizard.” The specific name, “dorsalis”, comes from the Latin word dorsum meaning “spike”, in reference to a row of enlarged keeled scales on the middle of the lizard’s back which form a crest that extends almost to the tip of its vent. Dipsosaurus is a monotypic genus with D. dorsalis being its only recognized species.
The desert iguana is a blunt, medium-sized lizard which grows to 24 inches, including the tail. They are pale gray-tan to cream in color with a light brown reticulated pattern on their backs and sides. Down the center of the back is a row of slightly-enlarged, keeled dorsal scales that become slightly larger as you move down the back. The reticulated pattern gives way to brown spots near the back legs, turning into stripes along the tail. The tail is usually around one-and-a-half times longer than the body from snout to vent. The belly is pale. During the breeding season, the sides become pinkish in both sexes.
Iguanas have long limbs with five free toes ending in sharp claws, distinct eyelids, large external eardrums and often a throat pouch.
Diurnal, these reptiles are known for their impressive courting and defensive displays. They will raise their bodies and bob their heads vigorously.
Their preferred habitat is largely contained within the range of the creosote bush, mainly dry, sandy desert scrubland below 3,300 feet in elevation. It can also be found in rocky streambeds up to 3,300 feet. In the southern portion of its range this lizard lives in areas of arid subtropical scrub and tropical deciduous forest.
These lizards can withstand high temperatures and are out and about after other lizards have retreated into their burrows. They burrow extensively, and will often climb into shrubs for shelter and defense. Their burrows are usually constructed in the mounds of sand that accumulate around the bases of bushes like the creosote. They also often use ready-made burrows of kit foxes and desert tortoises.
Mating takes place in the early spring. It is believed that only one clutch of eggs is laid each year, with each clutch having 3-8 eggs. The hatchlings emerge around September.
Desert iguanas are primarily herbivorous, eating buds, fruits and leaves of many annual and perennial plants. They are especially attracted to the yellow flowers of the creosote bush. Predators of these iguanas and their eggs are birds of prey, foxes, rats, long-tailed weasels, some snakes, and humans.
Tim Revell, PhD, has made a study of the sleeping habits and patterns of the desert iguana. His observations show that in the presence of predators, such as sidewinder snakes,  desert iguanas engage in asynchronous eye closure, such that the eye that is facing the snake is open while the other is closed, suggesting the desert iguana has the ability to undergo unihemispheric slow wave sleep, in which one side of the brain is asleep while the other side is awake and alert. This is in contrast to normal sleep where both eyes are shut and both halves of the brain show reduced consciousness. In unihemisperic slow wave sleep, one half of the brain is in deep sleep, with a form of non-rapid eye movement sleep taking place behind the closed eye.
A research team led by Bryan Fry at the University of Melbourne, Australia, has produced data to indicate that some species of iguana possess toxin-producing oral glands, although this has not been confirmed as applying to the desert iguana.