COMPARATIVE SKELETAL MORPHOLOGY 



In this section I describe variation in the iguanine skeleton by region and compare iguanines 

 with basiliscines, crotaphytines, morunasaurs, and oplurines. These descriptions 

 emphasize variation that is relevant to an analysis of relationships among iguanine genera 

 and are not intended to be exhaustive. For more detailed descriptions of the head skeleton 

 that include features common to all iguanines I refer the reader to Oelrich (1956), whose 

 terminology is followed below. 



SKULL ROOF 



The iguanine skull roof, or the superficial dermatocranial elements of the skull proper, 

 consists of the full complement of bones thought to be plesiomorphic for squamates. Other 

 iguanians may lack some of these bones, most commonly lacrimals and postfrontals. The 

 quadrate, a splanchnocranial bone, is also described in this section. Bones of the iguanine 

 skull roof, palate, braincase, and lower jaw are illustrated in Figures 5 and 6. 



Premaxilla (Figs. 5A, 6A, 7, 8). The premaxilla is the anteriormost bone in the skull. 

 Postembryonically, it is a median, unpaired bone that is sutured laterally with the maxillae, 

 posterodorsally with the nasals, and posteroventrally with the vomers. The premaxilla 

 bears a ventrally directed incisive process near its posteroventral end on the midline (Fig. 

 7). Foramina for the maxillary arteries (Oelrich, 1956) penetrate the premaxilla on either 

 side of the incisive process. In most iguanines (Brachylophus, Cyclura, Ctenosaura, 

 Iguana, Dipsosaurus, and Sauromaliis) and all outgroups examined, the ventral surface of 

 the premaxilla bears well-developed posteroventral extensions where it sutures with the 

 maxillae. A weak ventral crest runs along the posterior edge of the premaxilla from its 

 posterolateral comers to the base of the incisive process. This crest is generally not pierced 

 by the foramina for the maxillary arteries. In Amblyrhynchiis, the posterolateral extensions 

 of the premaxilla are small and the posterolateral corners of this bone are concomitantly 

 closer to the base of the incisive process (Fig.7 A) than are those of other iguanines (Fig. 

 7B). Conolophiis differs from the typical iguanine pattern in having large posteroventral 

 crests that continue up the sides of the incisive process and are pierced or notched by the 

 foramina for the maxillary arteries (Fig. 7C). In Sauromaliis slevini these foramina also 

 pierce the ventral crest of the premaxilla; however, the condition does not appear to be 

 homologous with that seen in Conolophus. In Conolophus the crests are pierced because 

 of their enlargement, while in S. slevini the foramina appear to have moved posteriorly. 



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