Phylogenetic Systematics of I guanine Lizards 133 



(excepting Ctenosaura, which is properly a Central and South American form)." H. M. 

 Smith (1946:101) says of his herbivore section (iguanines), "this includes the large, 

 primitive iguanids." 



The notions that iguanines are "primitive" iguanids and that they are ancestral to 

 sceloporines and crotaphytines are false. While it is true that iguanines lack certain derived 

 features seen in these other groups, this is simply a manifestation of the mosaic nature of 

 evolution, for the converse is also true. Sceloporines and crotaphytines lack derived 

 characters seen in iguanines. Iguanines are derived relative to sceloporines and 

 crotaphytines in numerous characters, among them the possession of caudal vertebrae with 

 two pairs of transverse processes, the posterior location of the supratemporal bone, 

 herbivory and associated morphological adaptations (flared tooth crowns, colic valves), 

 and large body size. Because some of the derived characters of iguanines occur nowhere 

 else within Iguanidae, iguanines cannot be considered ancestral to any other iguanids. 



In the early 1960's, Etheridge constructed a phylogeny for iguanines as part of his 

 scheme of relationships for the entire Iguanidae (Fig. 4). This scheme was never intended 

 to be published (Etheridge, pers. comm.), and it is difficult to evaluate because the reasons 

 for the various groupings were not specified. Other than differences in resolution, the 

 results of the present study differ from Etheridge's scheme in two primary ways: While I 

 consider Dipsosaurus and Brachylophus to be outside of a monophyletic group formed by 

 the remaining iguanines, Etheridge considered Brachylophus to be the sister group of the 

 Galapagos iguanas, and he considered Dipsosaurus to be the sister group of Sauromalus. 

 Although the relationships proposed by Etheridge can be supported by particular shared, 

 derived characters (e.g., lack of autotomy septa in caudal vertebrae oi Brachylophus and 

 the Galapagos iguanas; anterior position of parietal foramen in Sauromalus and 

 Dipsosaurus), the weight of the evidence suggests different relationships and necessitates 

 that the distribution of these derived characters is partly the result of convergence. The full 

 evidence leading to this conclusion is given in the diagnoses of the various monophyletic 

 groups recognized in the present study and will not be repeated here. 



The only published study dealing with relationships among all the iguanine genera is 

 that of Avery and Tanner (1971). As I noted in the Introduction, these authors used an 

 artificial system for assessing similarity, used many characters that are probably correlated, 

 made no attempt to determine character polarity, and did not specify how their similarity 

 data were used to construct their phylogenetic tree. Furthermore, Avery and Tanner's 

 conclusions are obscured by self-contradictory, vague, and ambiguous statements. For 

 example, they state (p. 69) that "the osteological characters . . . indicate that Oplurus and 

 Chalarodon are more closely related to each other than to the iguanines, and Oplurus is the 

 Madagascarian genus most closely related to the Western Hemisphere iguanines." In one 

 place (p. 68), Avery and Tanner claim that Ctenosaura is certainly ancestral to the Western 

 Hemisphere iguanines, but their phylogenetic tree (Fig. 3) suggests that Dipsosaurus, a 

 Western Hemisphere iguanine, is not derived from Ctenosaura, and later (p. 73) they seem 

 to consider Ctenosaura ancestral to only Cyclura and Sauromalus. One of Avery and 

 Tanner's 1 1 numbered conclusions is that Iguana and Ctenosaura evolved from a common 



