The color may also ligthen after basking in the sunlight with yellowish and orange markings becoming evident along the sides. Adult males and females are dimorphic. Adult males have well developed dorsal crests and small dewlaps. The dewlap, the crescent of skin that can be extended under the throat, is not inflated. A small bone bows out to extend the dewlap during times of threat, courtship, or while defending territory.
Females lack obvious crests.
There is considerable variation with age and sex and therefore identification may be difficult. The lizards have tails ringed with rows of sharp, curved spines, hence the name spiny-tailed iguana. The spines down the back are short. The ctenosaur is generally herbivorous, particularly on legume fruits, but is also known to have a diverse carnivorous diet that consist of small animals. Ctenosaurs have eaten rodents, bats, frogs, small birds, and a variety of insects.