The common chuckwalla (Sauromalus obesus) is a large, dorso-ventrally flattened, dark-bodied lizard with loose folds of skin on the neck and sides. The dorsum has small granular scales and the tail has a blunt tip and a broad base. The rostral scale is absent. The young are cross-banded with brown and gray-brown on body and tail. As reported by Kwiatkowski and Sullivan (2002a), adult males have 2 color patterns, those found on South Mountain are bicolored with a Black head, body, and limbs, and a reddish orange tail. Those in south-central Arizona (south of the Salt and Gila Rivers) are also bicolored; however, the tail is yellow to yellowish white. The remaining populations are tricolor with a black head and limbs, a yellowish white tail, and orange saddles on the torso. These include those populations north of the Salt and Gila Rivers. Throughout their range, females are a mottled brown or gray and cryptic. The females (and also males in southwestern Utah) tend to retain juvenile cross bands. The species is the largest native iguanid in the U.S. The adult length is 11-16.5 in (28-42 cm).
The species differs from other U.S. iguanid lizards in being larger and more robust, lacking extended toe tips, lacking head spines and enlarged middorsal scales, and having no overlapping scales at the upper edge of the orbit.
They bask on rocks during the day. They are inactive in cold temperatures or extreme heat. Chuckwallas in Arizona make their homes in rock crevices. A frightened chuckwalla will retreat into a rocky crevice and wedge itself in sideways by inflating its body. The following is from Prieto and Ryan (1978), “in a challenge display a male chuckwalla compresses his trunk, partially extends his dewlap, orients laterally toward his opponent and performs rapid head nods with partial flexion of his front legs. The head nodding follows a specific sequence: 2 complete up and down movements, two intermediate nods and 2 shorter nods.”
Mating occurs from May to June. Chuckwalla laid one clutch of 5-16 eggs from June to August; the eggs are laid underground. The clutch size increases with the female body size. Females may only lay eggs every second year.
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