Chuckwalla Doug Slater. Mojave National Preserve has 36 documented reptile species. Reptiles of the class Reptilia are cold-blooded, regulating their body temperature based on environmental conditions. Their thick, scaly skin comprised of keratin, a protein found in human nails, minimizes water loss through evaporation. Chuckwalla: (Sauromalus obesus) Loose skin, granular scales, and a distinctive paunch, Chuckwallas are the second largest lizard in the US next to the Gila Monster. Fond of yellow flowers, such as those found on brittle bush, 10-16 inch chuckwallas are observed along lava flows and rocky areas throughout the preserve. During breeding season, adults will develop a pinkish hue. Elusive and evasive, chuckwallas can foil predators by trapping themselves in crevices through inflating their bodies.