Phylogenetic Systematics oflguanine Lizards 69 



of Amblyrhynchus, Conolophus, and Sauromalus are relatively short, often less than two- 

 thirds the length of the first ceratobranchials (Fig. 33B). Iguana iguana and both species of 

 Brachylophus have long second ceratobranchials, invariably much longer than the first 

 ceratobranchials (Fig. 33C). The long second ceratobranchials support the gular fans seen 

 in these species. 



Another variable character in the hyoid skeletons of iguanines is the proximity of the 

 two second ceratobranchials to one another. In all iguanines except Amblyrhynchus and 

 Sauromalus, these elements contact each other along the midline for most or all of their 

 lengths (Fig. 33A,C); sometimes they are separated by a small gap where they meet the 

 body of the hyoid. In Amblyrhynchus and Sauromalus the second ceratobranchials are 

 largely or entirely separated from one another (Fig. 33B). 



Most of the outgroup taxa examined in this study have second ceratobranchials of 

 intermediate size, these elements being slightly shorter than the first ceratobranchials. 

 Some Basiliscus have slightly longer second ceratobranchials, but they are not nearly as 

 long as those of Brachylophus and Iguana iguana. Crotaphytus and Gambelia have short 

 second ceratobranchials, about half the length of their first ceratobranchials. Thus, very 

 long second ceratobranchials are almost certainly apomorphic for iguanines, and, unless 

 crotaphytines are the sister group of iguanines, short ones are probably also apomorphic. 

 Separation of the second ceratobranchials along the midline is unequivocally apomorphic, 

 based on the outgroups used in this study. 



AXIAL SKELETON 



Presacral Vertebrae (Figs. 34, 35, 36, 37). The presacral vertebrae (Fig. 34) of all 

 iguanines are procoelous and possess supplementary articular surfaces, zygosphenes and 

 zygantra, medial to the zygapophyses. Iguanine cervical vertebrae, defined as those 

 vertebrae anterior to the first one bearing a rib that attaches to the sternum (Hoffstetter and 

 Gasc, 1969) and including the atlas and axis, invariably number eight. From four to seven 

 ventrally keeled intercentra are present on the atias, the axis, and between the centra of the 

 anterior cervical vertebrae, decreasing in size posteriorly. The intercentrum of the axis 

 fuses with its centrum late in postembryonic ontogeny. There is regional differentiation in 

 the shape of the presacral vertebrae: the anterior and posterior presacrals are relatively short 

 compared to those in the middle of the column. 



The number of presacral vertebrae in iguanines ranges from 23 to 27 (Table 4). Most 

 species exhibit a strong statistical mode of 24 presacral vertebrae, with occasional variants 

 having 23 or 25. I judge this to be the plesiomorphic condition because it is seen in all 

 species of basiliscines, crotaphytines, morunasaurs, and oplurines that I have examined. 

 Within the genus Ctenosaura, three species, C. clarki, C. defensor, and C. 

 quinquecarinata, have a modal number of 25 presacral vertebrae. Because the apomorphic 

 condition occurs in only some Ctenosaura, this character reveals nothing about 

 relationships among my basic taxa. I used differences in modal numbers of presacral 

 vertebrae as a character only in an analysis of relationships within Ctenosaura. 



