The genus Urosaurus (the tree and brush lizards) belongs to the New World iguanian family Phrynosomatidae. They can be distinguished from members of the genus Sceloporus by the presence of a gular (under neck) fold and granular lateral scales. They can be distinguished from members of the genus Uta by the presence of enlarged (sometimes only slightly) dorsalscales. It has been used as a model system in lizard life-history studies, and populations produce two or more clutches of eggs per year (Michel 1976, Ballinger 1984). Field studies have also shown a cost of reproduction in a natural New Mexico population of the species Urosaurus ornatus (Landwer, 1994).