Introduction 



The lizard genus Sauromahis consists of a diverse group of diumaJ herbivores inhabiting the 

 deserts of southwestern United States and northwestern Mexico, including more than 26 islands in 

 the Gulf of California Commonly known as chuckwallas, these large iguanids generally live on 

 volcanic or granitic substrates, although some species also prefer nearby arroyo bottoms. 

 Chuckwallas display a wide array of color patterns that undergo a degree of ontogenetic 

 transformation, sometimes becoming sexually dichromatic. Body size varies from large to small, 

 although when compared to other iguanid lizards, chuckwallas are approximately one half the size 

 of the largest members in the family. Some species exceed an impressive snout-vent length of 

 more than 300 mm, while others reach 220 mm or less. 



The genus is well supported as a natural group within Iguanidae based on numerous 

 morphological novelties (de Queiroz 1987). These unique features are associated with 

 chuckwallas preference for rocky habitats and their ability to retreat into rock crevices to seek 

 shelter Their dorsoventrally compressed body results from a compression of both the pectoral 

 and pelvic girdles, a more slender mandible, reduced neural spines, and the absence of a mid- 

 dorsal scale row Once inside a crevice, chuckwallas inflate their lungs if harassed, eflfectively 

 wedging them into place and making extraction diflBcult. 



As many as nine species have been described within Sauromalus, although only seven 

 species are recognized at present (Table 1) In recent years, many authors have called into 

 question the number species within the genus and the geographical boundaries in which they occur 

 (Robinson 1972; Case 1982, Stebbins 1985, de Queiroz 1987). These taxonomic controversies 

 are primarily the result of outdated systematic methodologies, insufficient diagnoses, and the 

 absence of a reported type locality for the holotype, Sauromalus ater The last taxonomic study 

 of the entire genus was completed by Shaw (1945) Currently, the only formal phylogenetic 

 analysis of the chuckwalla species is a unpublished Master's thesis (Hollingsworth, 1995) that is 

 being edited for publication. 



As this bibliography shows, chuckwallas have been the focus of numerous biological 

 pursuits. Sauromalus obesus has been the main focus of investigation in studies requiring large 

 sample sizes and long-term observation Their wide-use in research is primarily the result of their 

 accessibility from the United States. Some researchers have undertaken the extra eflFort in 

 documenting the diet, behavior, ecology, and evolution of the insular endemics, S. hispidus and S. 

 varius, which are found on the Mexican islands in the mid-rift region of the Gulf of California. 

 Other species, such as, S. aier, S klauberi, S. slevini and S australis have received less attention. 

 The sporadic literature on these species is most likely due to their inaccessibility on small islands in 

 the Gulf of California and the remoteness of Baja California 



