94 University of California Publications in Zoology 



the colon (Iverson, 1980). Because of the difficulties involved in outgroup comparison 

 with the colic characters, I used them only at hierarchical levels less inclusive than 

 Iguaninae as a whole. 



Although much variation exists in the modal number of colic valves among iguanine 

 taxa, this number is positively correlated with (maximum?) body size and does not change 

 significantly during the postembryonic ontogeny of a given species (Iverson, 1980). Lack 

 of a thorough study of the relationship between valve number and body size makes 

 comparison of taxa that differ in body size problematic, and I have chosen not to use the 

 numbers of different types of colic valves as systematic characters. 



EXTERNAL MORPHOLOGY 



Unlike the arterial and colic characters, which were obtained from comparative studies, the 

 following characters were taken primarily from generic diagnoses or are based on personal 

 observations. No adequate comparative descriptions of these characters exist in the 

 literature, and I therefore describe them in more detail than the arterial and colic characters. 



The scutellation of the iguanine head is complex and is potentially the source of many 

 systematic characters. I note here only some obvious intertaxic differences and characters 

 that have been used by previous authors. 



Scales of the Snout and Dorsal Head. In most iguanines the snout terminates anteriorly 

 in a median, azygous rostral scale. Sauromalus differs from all other iguanines in that it 

 usually lacks an unpaired, median rostral (H. M. Smith, 1946: Fig. 38); the anteriormost 

 snout scales above the lip are paired and separated by a median suture that meets the lip 

 margin. According to Gates (1968), this character occurs in about 78% of S. obesus. All 

 basiliscines, crotaphytines, morunasaurs, and oplurines possess a median, azygous rostral 

 scale, indicating that the condition seen in Sauromalus is apomorphic within iguanines. 



The other scales in the snout region also exhibit differences among iguanines. In most 

 taxa they are relatively small, about the same size as the remaining dorsal cephalic scales. 

 In Iguana and some Cyclura, however, these scales form large plates. Interspecific 

 variation in this character is great within Cyclura (figures in Schwartz and Carey, 1977), 

 ranging from the small scales much like those of other iguanines in C carinata, C. pinguis, 

 and C. ricordii to the large plates of C. cychlura and C. nubila. Cyclura collei and C. rileyi 

 are intermediate, and the horns of C. cornuta are difficult to compare with the conditions 

 seen in other taxa. Because outgroup comparison suggests that enlarged rostral scales are 

 apomorphic (only Lxiemanctus among the outgroups examined has enlarged snout scales), 

 either (1) the occurrence of this feature in Iguana and some Cyclura is convergent; (2) it 

 indicates that Iguana is the sister group of some part of a paraphyletic Cyclura; or (3) 

 enlarged snout scales is a synapomorphy oil guana plus Cyclura, and some Cyclura have 

 evolved small snout scales secondarily. Only a consideration of other characters can 

 resolve this question. 



Amblyrhynchus and Conolophus are similar to one another and differ from all other 

 iguanines in the scalation of the dorsal surface of the head. In these two genera the dorsal 



