There are approximately 4,000 different species of lizards living around in the world, making this the largest group of reptiles. Lizards come in a wide variety of sizes and shapes. One species of gecko is less than 2 centimeters (1 inch) long, while a monitor lizard can reach 3 meters (10 feet) in length. Most lizards have four well-muscled legs with clawed feet. However, some are “limbless,” having lost the need for legs to get around. Instead, these lizards slither like snakes.

Lizards occupy diverse habitats, including deserts, rainforests, marshes, and prairies. One type of iguana even lives by the sea and feeds on marine algae. As is true of all successful living organisms, lizards have evolved adaptations—specialized physical and behavioral traits—that have helped them survive in their preferred environments. Just as tree-dwelling chameleons have tails that help them grasp branches when climbing, some aquatic species have tails shaped like an oar that help them swim.

An important environmental factor for most lizards is temperature. How they cope with temperature determines when they’re active and when they sleep. Desert-dwelling lizards have a mix of physical and behavioral adaptations that allow them survive the extremes of heat and cold that typify desert environments. For example, many lizards can change their skin color, which can speed up or slow down heat absorption. This can be important, because lizards are cold-blooded and cannot produce their own heat internally.

A desert lizard alters its behavior by season and by day, carefully timing activities to keep its body temperature within an optimal range. It may come out in the morning and bask in the sunlight before searching for food. If the temperature gets too hot, the lizard may seek shelter under a rock overhang, within a crevice, or even buried in sand until later in the day. Some species, such as the Gila monster, demonstrate different activity patterns throughout the year. During the cooler, wet season, Gila monsters are diurnal, which means they are active during the day. However, they are predominantly nocturnal, or active at night, during the hottest months of the year.

Like all nocturnal animals, nocturnal lizards possess adaptations that help them navigate in low-light conditions. Their pupils open far wider than a human’s can, maximizing the amount of light that can enter the eye. As is true with both the Western banded gecko and the desert night lizard, nocturnal lizard pupils are vertically oriented slits, not rounded like ours. In addition, the retinas of nocturnal eyes have a higher percentage of extremely light sensitive cells called rods. The sensitivity of rods is about 500 times greater than that of cones, the other type of light sensitive cell. This specialized vision helps nocturnal lizards hunt and avoid predators even in the darkest hours of night.

To learn about the unique adaptations of one unmistakable desert-dwelling reptile, check out Horned Lizard.

To learn about the only venomous lizard in the U.S., check out Gila Monster.

To learn more about the physical characteristics of the desert and the animals that inhabit it, check out Desert Biome.

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