Phylogenetic Systematics of I guanine Lizards 8 1 



with vertebrae 13 and 14, and their cartilaginous ventral portions unite with one another 

 before attaching to the posterior end of the sternum. The remaining ribs are simply termed 

 postxiphisternal. The bony anterior postxiphistemal ribs are often as long as their 

 xiphisternal counterparts, but there is a progressive reduction in their length posteriorly. 

 The posteriormost ribs are shorter than the sacral pleurapophyses. Lumbar vertebrae, 

 posterior presacral vertebrae lacking ribs, are not found in iguanines. Very rarely, the ribs 

 of the posteriormost presacral segment are fused to the vertebra. 



Etheridge (1965b) described variation in the abdominal skeleton (postxiphistemal 

 inscriptional ribs) of iguanids. All iguanines were reported to exhibit a pattern in which all 

 postxiphistemal inscriptional ribs are attached to their corresponding dorsal bony ribs. In 

 some iguanines, all of these inscriptional ribs end free, while in others the members of one 

 or more of the anterior pairs may join midventrally to form continuous chevrons. Based on 

 Etheridge's (1965b) findings and my own observations, the iguanine genera exhibit the 

 following morphologies in the abdominal skeleton: (1) continuous chevrons absent 

 (Dipsosaurus, Sauromalus); (2) continuous chevrons present or absent (Amblyrhynchus, 

 Conolophus, Ctenosaura, Cyclura, Iguana); and (3) continuous chevrons present 

 (Brachylophus). The number of continuous chevrons and other enlarged postxiphistemal 

 inscriptional ribs may exhibit taxon-specific pattems, but because the fragile abdominal 

 skeleton is often destroyed in skeletal preparations, I have not been able to examine enough 

 specimens to assess these pattems adequately. 



In the outgroups that I have examined, postxiphistemal inscriptional ribs that form 

 continuous midventral chevrons are found only in momnasaurs; however, because they 

 share the common feature of having at least some inscriptional ribs that bear no traces of 

 attachment to the bony ribs, Etheridge (pers. comm.) believes that the oplurine pattem is a 

 transformation of that seen in momnasaurs. Basiliscines and crotaphytines are similar to 

 Dipsosaurus and Sauromalus in their lack of continuous chevrons. Thus, evidence bearing 

 on the polarity of this character is equivocal, and I did not use it in my initial analysis of 

 relationships among iguanine genera. 



PECTORAL GIRDLE AND STERNAL ELEMENTS 



The iguanine pectoral girdle and stemal elements (Fig. 40) are closely associated and form 

 a complex functional unit composed of six pairs of elements plus two median, unpaired 

 ones. Some of these elements are composed entirely of calcified cartilage, while others are 

 bony. All iguanines possess all 14 elements: suprascapulae, scapulae, coracoids, 

 epicoracoids, clavicles, interclavicle, sternum, ana xiphistema. 



Suprascapulae (Fig. 40). These are paired fan-shaped elements composed of calcified 

 cartilage that extend continuously from the dorsal edges of the scapulae. The suprascapulae 

 lie just extemal to the posterior cervical and the anterior thoracic bony ribs. They are not 

 attached directly to the axial skeleton, but ride over the bony portions of the ribs. As in 

 most squamates, the only direct skeletal attachments between pectoral girdle and axial 

 skeleton are through the stemum and cartilaginous portions of the anterior thoracic ribs. In 



