Phylogenetic Systematics oflguanine Lizards 79 



con + .. / . f/^ipv^.^^ con- 



FIG. 38. Lateral views of the ninth caudal vertebrae of (A) Dipsosaurus dorsalis (KdQ 22) and (B) 

 Iguana iguana (MVZ 78384), showing differences in the size of the dorsal midsagittal processes. Scale 

 equals 2 mm; anterior is to iJie right. Abbreviations: con, articular condyle; ns, neural spine; p, dorsal 

 midsagittal process. 



relatively small and do not continue as far posteriorly in the caudal sequence (Fig. 38B). 

 Although they may be present beyond the sixth caudal vertebra, I have never observed 

 them beyond the tenth. The caudal sequences oi Brachylophus and Iguana consist of more 

 than 55 vertebrae; thus, the processes are not present beyond the anterior fifth of the 

 sequence. 



Although the evidence is somewhat equivocal, outgroup comparison favors the 

 interpretation that the condition of the midsagittal processes of the caudal vertebrae seen in 

 Brachylophus and Iguana is apomorphic. The alternative condition occurs in 

 crotaphytines, morunasaurs, and oplurines, but basiliscines are similar to Brachylophus 

 and Iguana. In basiliscines, the small, fmlike processes are rarely found posterior to the 

 fifth caudal vertebra. Basiliscines, Brachylophus, and Iguana are all arboreal, suggesting a 

 possible functional relationship between the morphology of the caudal vertebrae and use of 

 the tail in arboreality. 



Ribs (Fig. 39). Variation in the numbers and the morphology of various kinds of ribs 

 has served as the basis for characters in previous systematic studies of iguanids (Etheridge, 

 1959, 1964a, 1965b, 1966); but iguanines are conservative in most of these features. Like 

 those of all iguanids, iguanine ribs are holocephalous and most have two parts: a bony 

 dorsal portion and a cartilaginous ventral portion, the inscriptional rib (Etheridge, 1965b). 

 The length of the inscriptional ribs is highly variable from one region of the vertebral 

 column to another, and at the posterior end of the presacral series these elements are often 

 lacking. 



Cervical ribs, those ribs anterior to the first ribs that are attached to the sternum, 

 typically number four pairs in iguanines, beginning on the fifth presacral vertebra (very 



