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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 analysis. 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 developed 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 condition is widespread within Iguania and it was not included in the phylogenetic analysis. Finally, in Gambelia copei (eight of eight), relatively 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 condition (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 parietal 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 compressed 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 ontogeny, the posterior edge of the parietal roof becomes 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 constricted 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 robust 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 character 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 inflected supratemporal processes. Gambelia also possess 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 supratemporal processes continue posteriorly well beyond the squamosal to its terminus. As a result, in Gambelia,
16 BULLETIN CARNEGIE MUSEUM OF NATURAL HISTORY NO. 32 Fig. 8.-Lateral view of the skull of Crotaphytus dickersonae (REE 2777, adult male, SVL = 116 mm). Scale = 5 mm. the processes appear less robust and do not arch as far above the plane of the parietal roof. This variation, which can be used to quickly differentiate between skulls of these genera, could not be polarized due to variation in the outgroups. Szcprate~nporals (Character 10; Fig. 9, 10). -The supratemporals are small paired bones that lie in ventrolateral grooves in the supratemporal processes of the parietal in most crotaphytids (Etheridge and de Queiroz, 1988; Frost and Etheridge, 1989). The supratemporals are more exposed posterolaterally and form the major portion of the process at Fig. 10.-Supratemporal region of Gambelia silus (CAS 227 13, adult male, SVL = 101 mm). The vertical hatching denotes the exposed portion of the supratemporal bone. Jug = jugal, Par = parietal, Pte = pterygoid, Pto = postorbital, Qua = quadrate, Squ = squamosal. Scale = 5 mm. its articulation with the quadrate and squamosal. The tongue-in-groove articulation of each supratemporal with the parietal is well developed in all crotaphytids except Gambelia silus (Fig. 9, 10). Indeed, in most G. silus that could be coded for this character (25 of 28), the supratemporal does not sit in a groove, but lies along the lateral surface of the supratemporal process (Fig. 10). This variation is occasionally observed in G. wislizenii (four of 49), C. antiquus (one of four), and C. collaris (one of 5 I). In iguanian lizards, the tongue-in-groove relationship between the supratemporal and supratemporal process is seen only in crotaphytids and the tropidurid genus Liolaemus and therefore is here considered to be derived within Crotaphytidae. The condition observed in G. silus may be a reversal because some individuals do possess the rare grooved condition seen in few iguanian lizards. Sepfomaxillae (Character 1 1; Fig. 2-5, 7).-The septomaxillae are paired sheets of bone situated in the anteromedial nasal capsule where they form the floor of the nasal passages and the roof over the Fig. 9.-Supratemporal region of Crotaphytus vestigiion (REE Jacobson's organ (Oelrich, 1956; Jollie, 1960). In 2935, adult male, SVL = 125 mm). The vertical hatching denotes the exposed portion of the supratemporal bone. Jug = jupl, Par Gambelia wislizenii and G. copei, the septomaxillae = parietal, pte = pterygoid, pto = postorbital, Qua = quadrate, are slender and more elongate than in either G. S~/US ~qu = squamosal. Scale = 5 mm. or Crotaphytus. It is likely that this condition is
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