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McGUIRE-SYSTEMATICS OF CROTAPHYTID LIZARDS -- -- Fig. 7.-Dorsal view of the anterior portion of the skull of Cro- raphytusgrismeri (MZFC 665 1, adult male, SVL = 92 mm). The vertical hatching denotes the cxtn frontonasal bone present in two of five specimens examined. Fro = frontal, Max = maxilla, . . Nas = nasal, Prf = prefrontal, Prm = premaxilla. Scale = 5 mm. Fig. 6.-Anterior portion of the orbit showing contact of the prefrontal and jugal bones (Croraphytus dickersonae, adult male. REE 2777, SVL = 116 mm). Jug = jugal, Lac = lacrimal, Max = maxilla, Pal = palatine, Prf = prefrontal. Scale = 2 mm. therefore, for the entire Tropiduridae. Because B. stump@ and U. acanthinurus are the only nontro- pidurid iguanian taxa examined here in which the nasals overlap the nasal process of the premaxilla, it is most parsimonious to code extensive overlap of the nasal process by the nasals as the derived state. Pre/i.ontals (Character 4; Fig. 2-4, 6, 7).-In all crotaphytids, the palatine process of the prefrontal broadly contacts the jugal just posterior to the lacrimal foramen (de Queiroz, 1987; Fig. 6). This condition was observed in Phrynosoma asio, Utna esul, U. inornata, U. notata, U. scoparia, some Pltyma- turus patagonicus payuniae, one of three Leioce- phalus macropus. Microlophus grayi, one of three Uranoscodon superciliosus, some Pristidactylus tor- quatus, Polychrus acutirostris, and some Po. marmoratus. In Phrynosoma asio and L'ma (as well as other sand lizards), this contact appears to be associated with loss of the lacrimal bone, which usually separates the prefrontal from the jugal in other iguanians. The contact of the prefrontal and jugal is considered to be the derived state and, thus, rep- resents a synapomorphy for Crotaphytidae. Although Norell (1989) stated that crotaphytids can be diagnosed by the derived loss of the prefrontals, clearly (as he stated elsewhere in the paper), he was referring to the loss of the postfrontals. Frontal (Character 5; Fig. 2-4,7,8).-A separate, median frontonasal bone (Fig. 7) is present in two of five Crotaphytus grismeri (MZFC 6650, 665 1). Although the sample size is small for this taxon, its presence in two specimens suggests that it is a poly- morphism rather than an aberration. A similar bone was observed only in one Phymaturuspallurna (REE 23 13). Although this feature sheds no light on the phylogenetic relationships within Crotaphytus, it appears to represent an additional autapomorphy for the species. The skulls of Gambelia \vislizenii, G. copei, and G. coronat are more depressed than those of Cro- taphytzcs and G. silus. Although this variation appears to be associated with several bones, it is per- haps best illustrated by comparing the shape and orientation of the frontal bone. In Crotaphytus and G. silus, this bone is more strongly convex, while in
BULLETIN CARNEGIE MUSEUM OF NATURAL HISTORY NO. 32 G. wislizenii, G. copei, and G. coronaf, this bone usually is relatively flat, providing little height to the midorbital region of the skull. A description of the frontal bone only partially explains the complex variation in skull height within crotaphytids. There- fore, the character is here defined as "skull depressed" or "skull vaulted." Although a vaulted midorbital region of the skull is the more common condition within Iguania, this character could not be polarized. Norell (1 989) described the fossil taxon Gatnbelia coronaf based in part on a broad frontal that is transversely concave with supraorbital ridges. Many Gambelia have broad frontals; however, the dorsal surface is usually flat. Only one of 53 G. wislizenii (REE 2792) had weakly developed supraorbital ridges with a slight concavity and no G. copei were examined with this condition. Garnbelia silus also usually lack the supraorbital ridges; however, three of 31 had well-developed supraorbital ridges with strong transverse concavity. Although this condition cannot be considered unique to G. coronat, it appears to be a useful diagnostic feature for the species. Additional fossil material will be required in order to determine if this character is variable as in other Gambelia. The frontal may bear supraorbital ridges that give it a concave appearance in some Crotaphyfus, although, as in Garnbelia, it is only infrequently present. Among the outgroup taxa, a transversely concave frontal was observed in Eny- alioides laticeps, Basiliscus basiliscrrs, B. plumifrons, B. vittatus, Corytophanes hernandezi, some Cory- tophanes cristatus, some Laemanctus longipes, some Phymatuncs palluma, some Leiocephalus carinattcs, L'ranoscodon srcperciliosus, Urotnastyx hardwickii, Physignatltus lesueurii, Hydrosaurus arnboiensis, Brookesia kersteni, Enyalitis perditus, Polychrus marmoratus, and P. acutirostris. Therefore, this character could not be polarized. Nore11 (1 989) considered the frontoparietal suture anterior to the posterior extent of the orbit to be an additional autapomorphy of Garnbelia coronat. Al- though it is possible that this condition is an artifact resulting from damage to the fossil (dorsoventral compression), it does appear as though the frontoparietal suture was indeed anterior to the posterior extent of the orbits. The postorbitals project more posteriorly in G. coronaf than in other crotaphytids, which may play some role in the anterior placement of the suture. Although this character is not phy- logenetically informative, it provides a diagnostic autapomorphy for the species. In articulated skulls of some iguanians, the suture that binds the frontal with the nasals and prefrontals takes the form ofa "W." However, this shape results from the extensive overlap of the frontal by the nasals and prefrontals. The underlying anterior border of the frontal is often squared off or may possess two small lateral processes that project anteriorly. In all crotaphytids, the anterior border of the frontal bears three well-developed processes, two lateral projections and one medial projection, that extend forward equidistantly. This condition occurs spo- radically within Iguania and could not be polarized. Therefore, this feature was not considered in the phylogenetic analysis. Postj?ontals. -The postfrontals are small bones that form part of the posterior border of the orbits in many iguanian species, but are absent or fused in all crotaphytids. Postfrontals are absent or oc- casionally present as minute elements in Phryno- soma and the phrynosomatid sand lizards, some Phytnaturus (Phymaturus palluma, some Phyrna- tlcrus punae), oplurids, Polychrus (contra Frost and Etheridge, 1989; verified in P. acutirostris and P. marmoratus), Basiliscus, Corytophanes, and Cha- maeleonidae. Although the absence or fusion of the postfrontal bones may eventually prove to be a synapomorphy for Crotaphytidae, the currently unre- solved nature of iguanian phylogeny prevents po- larization of this character. Postorbitals (Characters 6, 7; Fig. 2-4, 8).-The dorsal process of the postorbital is roughly triangular in cross section in all crotaphytids. The dorsomedial aspect is completely overlapped by the frontal and parietal while the ventral portion is exposed. Thus, in an articulated skull it appears as though a long process projects medially beneath the overlying frontal and parietal. This condition appears to be more extreme in Crotaphytus because the parietal and frontal overlap the postorbital more laterally in these lizards. However, the condition of the postorbital does not vary significantly between Crota- phytusand Gambelia. In the outgroup taxa, the frontal and parietal usually meet the dorsomedial portion of the postorbital without overlapping it exten- sively; the only obvious exceptions are hoplocercids, corytophanids, one of two Uromastyx acanthinurus, basal agamines (Physignathus and Hydrosaurus am- boiensis), and Ettyalius iheringi. A strong degree of overlap at this joint, which appears to provide additional structural support, is tentatively recognized as a synapomorphy of Crotaphytidae. The angle of the dorsal process often differs be-
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