54 University of California Publications in Zoology 



coronoid have a relatively slight ventral extension of this process compared to 

 Amblyrhynchus, Brachylophus, and especially Conolophus. 



Angular (Fig. 6B,C, 25). The angular is located on the ventral surface of the mandible, 

 forming sutures with the splenial anterodorsally and the prearticular posterodorsally on the 

 lingual surface of the mandible and with the dentary anteriorly and the surangular 

 posteriorly on the labial side. In Brachylophus, Ctenosaura, Cyclura, Dipsosaurus, and 

 Iguana, the angular extends far up the labial surface of the mandible so that it is easily seen 

 in lateral view (Fig. 25 A). The angulars of Amblyrhynchus, Conolophus, and Sauromalus 

 are restricted labially so that they are barely visible from the lateral side (Fig. 25B,C). 

 Compared to those of other iguanines, the angular of Sauromalus is relatively narrow. 

 Because the angulars of basiliscines, crotaphytines, morunasaurs, and most oplurines are 

 wide posteriorly and extend far up the labial surface of the mandible, I considered these to 

 be plesiomorphic conditions. In Oplurus, the width and labial exposure of the angular are 

 variable owing to varying degrees of reduction in this bone. 



Surangular (Fig. 6B,C, 26, 27). This bone forms the dorsal portion of the mandible 

 posterior to the coronoid and anterior to the articular facet. It fuses with the prearticular late 

 in ontogeny. Dorsal to its suture with the angular on the labial surface of the jaw, the 

 anterior extent of the iguanine surangular is variable (Fig. 26). In Amblyrhynchus, 

 Brachylophus, and Dipsosaurus the exposed part of the surangular barely extends to the 

 level of the apex of the coronoid, being covered by the dentary anterior to this level (Fig. 

 26A,B). In Conolophus, it extends slightly farther, to the level of the anterior slope of the 

 coronoid eminence. The surangulars of Iguana and Cyclura extend far forward, well 

 beyond the anterior slope of the coronoid eminence and often anterior to several of the 

 posteriormost dentary teeth (Fig. 26C). Sauromalus and Ctenosaura are intermediate and 

 variable within species; the surangular in each of these genera usually extends beyond the 

 anterior slope of the coronoid eminence, but falls short of the tooth row. Some members 

 of both genera exhibit a condition similar to that of Conolophus, and some Ctenosaura have 

 a surangular that extends beyond the posteriormost dentary tooth. 



Although the outgroups used in this study are also variable in the anterior extent of the 

 surangular, in none does it extend as far forward as in Iguana and Cyclura. Therefore, in 

 the absence of other information, it seems that a great anterior extent of the surangular is a 

 synapomorphy of these two taxa. If the basic taxa used in this study are monophyletic, 

 then a similar condition seen in some Ctenosaura must either be convergent, or the 

 character may have arisen initially as a polymorphism, or some Ctenosaura have reverted to 

 the ancestral morphology. 



On the lingual side of the mandible, ventral to the apex of the coronoid in the arch 

 between the ventral feet of this bone, a small portion of the surangular is variably visible in 

 iguanines (Fig. 27). In most iguanines, this part of the surangular is relatively large and 

 has the shape of a dome above the prearticular (Fig. 27 A). In Amblyrhynchus, 

 Conolophus, and Cyclura cychlura, the prearticular extends further dorsally, either 

 completely excluding the surangular from the lingual surface of the mandible (Fig. 27B) or 

 leaving only a thin sliver of it exposed. Although few small specimens were examined. 



