160 University of California Publications in Zoology 



Comments: Sauromalus has a large number of derived characters supporting its 

 monophyly, many of which are unambiguous (i.e., they do not occur in any other 

 iguanine). Ahhough several of these characters, such as the height of the neural spines, the 

 orientation of the suprascapulae, and the shape of the pelvic girdle, may be part of a single 

 adaptive complex manifested externally in a depressed body form, I have treated them as 

 separate synapomorphies. Because various combinations of the alternative states of these 

 morphologies occur in certain noniguanine taxa, there is no reason to believe that they must 

 always occur together. 



Sauromalus shares a large number of derived characters with Amblyrhynchus, 

 particularly in the shoulder girdle but not confined to this structure. Because 

 Amblyrhynchus shares even more derived characters with Conolophus, and because 

 Conolophus does not possess most of the derived characters shared by Amblyrhynchus 

 and Sauromalus, I interpret the derived characters shared by Amblyrhynchus and 

 Sauromalus as convergences. Perhaps this convergence results from similar functional 

 demands placed on the shoulder girdle by the saxicolous habits of the animals in both taxa. 

 The situation is complicated by the fact that all three taxa share two other derived characters: 

 limited lateral exposure of the surangular (37-B), and relatively short second 

 ceratobranchials (52-53-B). If one were to accept a sister-group relationship between the 

 Galapagos iguanas and Sauromalus based on these characters, then the many characters 

 shared by Amblyrhynchus and Sauromalus, but not Conolophus, could be interpreted as 

 additional synapomorphies of this hypothesized clade that have reversed in Conolophus. 

 However, because Sauromalus also shares a derived tooth morphology with Cyclura and 

 Iguana that does not occur in the Galapagos iguanas, I see no compelling reason to accept a 

 sister-group relationship between Sauromalus and the Galapagos iguanas. Furthermore, 

 even if such a relationship were accepted, interpreting the derived characters shared by 

 Amblyrhynchus and Sauromalus as convergent requires no more evolutionary changes than 

 hypothesizing a single origin for the derived state of each character, with reversal in 

 Conolophus. 



The most recent revision of Sauromalus is that of C. E. Shaw (1945), although works 

 of taxonomic significance have appeared subsequendy (Cliff, 1958; Tanner and Avery, 

 1964; Soule and Sloan, 1966; Robinson, 1972, 1974). The boundaries, monophyly, and 

 relationships of the species within Sauromalus need further study. 



Amblyrhynchina, new taxon 



Type genus: Amblyrhynchus B&\\ 1825. 



Etymology: Modification of Amblyrhynchus, the name of its type genus. 



Definition: The most recent common ancestor of the extant Galapagos iguanas, 

 Amblyrhynchus and Conolophus, and all of its descendants. 



