McGUIRE- SYSTEM.4TICS OF CROTAPHYTID LIZARDS jacent subcaudals and lateral caudals. Enlarged post- anal scales absent in males. Deep postfemoral dermal mite pocket present at hindlimb insertion. Femoral pores 16 to 2 1, femoral pores do not extend beyond angle of knee, separated medially by 17 to 25 granular scales. Subdigital la- mellae on founh toe 17 to 2 1. Coloration in LiJe. -Dorsal body coloration in adult males is vibrant aquamarine to cobalt blue over the entire dorsal surface of the body except the distal half of the tail. There is no trace of yellow as seen in Crotaphyfus collaris. The white component ofthe dorsal pattern is composed of large white spots and dashes on the body, a reticulated tail and hin- dlimbs, and forelimbs that are generally spotted or mottled. Transverse body bars are absent. Reticu- lations are always present on the superficial man- dibular and temporal regions. A broad white or off- white caudal vertebral stripe is present. The dorsal surface of the head is pale-colored, and is conspic- uously patternless. Olive green or burnt orange ven- trolateral coloration is lacking. The gular coloration is generally slate gray with a black central gular com- ponent. The peripheral gular pattern is the standard reticulate form. Anterior and posterior collar mark- ings are always present and the posterior markings often contact middorsally. The anterior collars are complete ventrally by way of black pigments present within the gular fold. A pair of black nuchal spots are not present middorsally between the anterior collar markings. Enlarged melanic axillary patches immediately posterior to the forelimb insertion are lacking. Large melanic inguinal patches are always present. The femoral pores are generally off-white to gray in color. Paired, melanic keels are always or nearly always present on the ventral surface of the caudal extremity. The coloration of females is much more subdued than that of males. The dorsal coloration is gray or brownish gray, rather than vivid blue, and females lack the melanic inguinal patches, black pigments in the gular fold, black central gular blotch, and white dorsal caudal stripe. Gravid females develop vivid orange or reddish lateral bars. The tail of re- productive females is bright lemon yellow. Size. -This species exhibits strong sexual dimor- phism with males reaching larger adult size (maxi- mum observed SVL = 1 16 mm) than females (max- imum observed SVL = 97 mm). Distribution (Fig. 46).-Isla Tiburon in the Gulf of California, Mexico, and the desert mountains of the adjacent Sonoran coastline (Sierra Bacha and Sierra Seri) between Punta Cirio (1 1.6 km S Pueno Libertad) and Bahia Kino, Mexico. Fossil Record. -None. Natural History. -No natural history data con- cerning this species have been published to date. Crotaphytus dickersonae apparently does not devi- ate significantly from other saxicolous Crofaphytus species with respect to basic aspects of its ecology and behavior. The species is common on south and east facing slopes with sparse vegetation and scat- tered granitic rocks of various sizes, with lizards generally observed basking on smaller rocks on these slopes. In coastal Sonora, C. dickersonae were ob- served on hillsides characterized by the following plant species: Bursera microphylla, Encelia farinosa, Jatropha cuneata. Pachycereus pringlei. Stenocereus thurberi, Lycium sp., and Harfordia tacroptera. The lizards Uta stansburiana, Cnemidophorus tigris, and Callisaurus draconoides are common on these hill- sides and very likely comprise a large component of the diet of C. dickersonae, a species that appears to prey heavily on lizards (based on gut content observations). This species tends to occur in similar habitats on Isla Tiburon, although juveniles ob- served on the island were concentrated around rocky outcroppings at the summits of the low hills rather than on the scattered rocks along the lower slopes of the hills. However, this observation should not be taken to represent a general phenomenon as very little time (two days) was actually spent on the is- land. Adults of both sexes were observed on 22 March 199 1 in coastal Sonora and adults and juveniles were active on lsla Tiburon on 24 March 199 1. Adult females did not bear gravid coloration, in- dicating that mating had not yet commenced. How- ever, an adult female observed on 14 April 1992 had striking orange gravid coloration indicating that mating takes place early in the spring in this species. Bright blue Crotaphyrus dickersonae males stand out boldly on the pale rocks while basking and one might expect this species to be nervous and difficult to approach. This is not the case, however. Indeed, a Red-tailed Hawk (Buteo jamaicensis) was ob- served to pass directly over a basking adult male C. dickersonae at a height no greater than I0 m without eliciting any observable reaction from the lizard. Illurrrations.-A black-and-white illustration of the lateral and dorsal head squamation of the holotype specimen is given in Schmidt (1922). Color pho-
BULLETIN CARNEGIE MUSEUM OF NATURAL HISTORY NO. 32 Gulf of California 40 krn Fig 46.-Geographic distribution of Cro~aphyrus dickersonac. The map depicts a small section of Sonoran coastline along the eastern margin of the Gulf of California.
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