NONSKELETAL MORPHOLOGY 



Iguanines exhibit considerable morphological variation in functional systems other than the 

 skeleton, and I have therefore used certain nonskeletal characters for which relatively 

 complete data on variation, both among all iguanine genera and for the four outgroups, 

 were easily obtained. Characters in this section were taken from diagnoses in revisions, 

 reviews, and faunal accounts as well as from the few comparative studies of nonskeletal 

 anatomy of iguanines. I also include some obvious characters that I noticed in the course 

 of this study. 



ARTERIAL CIRCULATION 



Zug (1971) was pessimistic about the systematic utiUty of the variation that he found in the 

 patterns of the major arteries of iguanids. Nevertheless, I found at least three characters in 

 his descriptions, as well as one additional character, that suggest monophyletic groups 

 within Iguaninae. Other arterial characters may also be useful for phylogenetic studies 

 within this taxon, but have not yet been studied in sufficient detail. Still other characters 

 are either invariant among iguanines (e.g., branching pattern of the carotid arches, 

 separation of the origins of dorsal aorta and subclavians) or variable within iguanine genera 

 (e.g., separate origin of mesenteries versus origin from a common trunk), and thus cannot 

 be used for examining relationships among these genera. These characters may be useful at 

 different hierarchical levels. 



It should be noted that Zug (1971) surveyed nearly all genera of Iguanidae, which 

 limited him to relatively small samples for each genus (a maximum of four specimens for 

 any iguanine genus). Zug did not examine Conolophus; my data are based on dissection of 

 a single C. subcristatus (CAS 12058). 



Zug reported that the subclavians of Brachylophus and Dipsosaurus are covered 

 laterally by a thin, flat ligament, while those of other iguanines pass laterally beneath 

 (=dorsal to?) a muscle bundle. My own observations on Dipsosaurus reveal muscle fibers 

 in the thin sheets of tissue that cover the subclavians just lateral to their origins from the 

 right systemic arch. Furthermore, whether muscular or ligamentous, the structures that 

 cover the subclavians are the posterior portions of the paired M. rectus capitis anterior or 

 their tendons, which originate on the ventral surfaces of the cervical vertebrae and insert on 

 the exoccipitals and basioccipital lateral to the occipital condyle. Thus, even if the reported 

 difference exists, it is a difference in the muscles rather than in the subclavian arteries. 



92 



