DESCRIPTION: A large (up to 310 mm or 12.25 ” from snout to vent), gray to brown lizard with black crossbars on the body and a long spiny tail. The posterior portion of the tail is usually banded. Coloration of individuals can change rapidly from pale gray to dark gray. Juveniles are bright green. A row of enlarged scales forms a ridge that runs from the neck, down the center of the back, and onto the tail.

DISTRIBUTION: Lizards from the genus Ctenosaura (see remarks) were introduced to the to the grounds of the Arizona-Sonora Desert Museum west of Tucson in the 1970s. They are still reproducing there but have not expanded their range beyond the immediate vicinity of the museum.

HABITAT: In their native Mexico, spiny-tailed iguanas are found in desertscrub and transitional zones between desertscrub and subtropical forest. They are often encountered in rocky terrain adorned with large columnar cacti.

BEHAVIOR: This diurnal lizard is often observed basking on rock outcrops, boulders, cacti, and trees. It has also been observed on fences and walls in urban areas. Juveniles are primarily arboreal. When threatened, this lizard will often retreat into a rock crevice, tree cavity, or woodpecker hole within a large columnar cactus. The spiny tail is then used to block out potential predators.