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McGUIRE-SYSTEMATICS OF CROTAPHYTID LIZARDS
tween Crotaphytus and Gambelia. In Crotaphytus,
the process is transversely oriented, while in Gam-
belia it is often anteromedially oriented. In many
cases this difference is very obvious. However, con-
tinuous variation within Gambelia prevented the
inclusion of this character in the phylogenetic anal-
ysis.
The postorbital meets the jugal and squamosal in
a tongue-in-groove articulation. In crotaphytids, the
postorbital bears the shallow groove in which the
jugal and squamosal lie. This condition is more de-
veloped in Gambelia, which bears a large flare that
broadly overlaps the jugal and squamosal on the
medial side of the joint. This feature is difficult to
evaluate in the outgroups due to the paucity of dis-
articulated skulls. However, it appears that this con-
dition is widespread within Iguania and it was not
included in the phylogenetic analysis.
Finally, in Gambelia copei (eight of eight), rela-
tively few G. wislizenii (four of 49; REE 425, 2792;
UIMNH 43378-79), and four of 3 1 G. silus (KU
121753, 121761, 121766, 121768), there is a small
projection or tubercle on the anterolateral surface
of the postorbital at the posterior edge of the orbit
(= character 7). In G. copei, it is usually larger and
more robust than in other Gambelia. This small
tubercle may function as an additional attachment
point for the skin ofthe head as does the larger dorsal
tubercle. The presence of this tubercle appears to be
unique within Iguania and may be a synapomorphy
for Gambelia, although its more developed state
may be further derived in G. copei. Nevertheless,
this feature is coded as a binary character with the
absence of a tubercle coded as the ancestral condi-
tion (state 0) and the presence of a tubercle as the
derived condition (state 1). Because they were poly-
morphic with respect to this character, G. wislizenii
and G. silus were assigned states c and d respectively.
Parietal (Characters 8, 9; Fig. 24, 8).-The pa-
rietal is a median bone that represents the major
element of the skull roof. Its complex shape includes
a trapezoidal roof with short anterolateral processes
and long posterolaterally projecting, laterally com-
pressed supratemporal processes. This shape changes
ontogenetically, although not to the extent seen in
some iguanids, polychrotids, and Leiocephalus (Eth-
eridge, 1959; de Queiroz, 1987; Pregill, 1992). In
juveniles, the parietal roof is roughly square, the
crests of the supratemporal processes are less robust
and project nearly directly posteriorly. During on-
togeny, the posterior edge of the parietal roof be-
comes increasingly constricted such that the lateral
borders of the roof converge. This gives the roof a
trapezoidal shape with the supratemporal processes
projecting posterolaterally rather than posteriorly.
Late in ontogeny, ridges may form along the lateral
and posterior borders of the parietal roof giving the
central portion a depressed appearance. The degree
of constriction of the posterior border of the parietal
roof during ontogeny differs between Crotaphytus
(Fig. 2) and Gambelia (Fig. 3, 4). In Gambelia, the
roof remains relatively broad posteriorly through-
out ontogeny and remains approximately twice the
width of the narrowest portion of the frontal bone.
In Crotaphytus (particularly males) the posterior
border of the parietal shelf becomes more constrict-
ed such that it is approximately equal in width to
the frontal bone or slightly wider. This constriction
is often most dramatic in adult male C. dickersonae,
although enough overlap occurs between species of
Crotaphytus that this was not considered as a sep-
arate character state. There is much variation in the
degree of constriction of the parietal roof within
Iguania, with the basal lineages of all but three fam-
ilies (Phrynosomatidae, not constricted; Coryto-
phanidae, constricted; Hoplocercidae, constricted)
having representatives with both states. Although
the polarity of the character could not be deter-
mined, Gambelia and Crotaphytus always differ in
the degree of constriction of the parietal roof. There-
fore, this feature was coded as an unpolarized binary
character with the Gambelia condition coded as state
0 and the Crotaphytus condition coded as state 1.
The supratemporal processes are extremely ro-
bust in Crotaphytus and, in lateral view, project well
above the temporal arches (Fig. 8). The lateral faces
of the processes are also concave. The robust char-
acter of the processes gives broad surface area for
the origin of the hypertrophied jaw adductor mus-
cles that these lizards possess. In all Crotaphytus
examined except some eastern C. collaris (1 3 of 5 1
specimens), the supratemporal processes are strong-
ly inflected ventrad at their distal ends. The skulls
of some eastern C. collaris tend to be more dorso-
ventrally compressed, which may result in less in-
flected supratemporal processes. Gambelia also pos-
sess ventrally oriented processes, although of a dif-
ferent character. The crests of the supratemporal
processes are well developed anteriorly, but quickly
taper posteriorly, usually terminating anterior to the
articulation of the process with the squamosal. By
contrast, in Crotaphytus, the crests of the supratem-
poral processes continue posteriorly well beyond the
squamosal to its terminus. As a result, in Gambelia,