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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-