Phylogenetic Systematics of I guanine Lizards 1 37 



Comments: Three of the five iguanine synapomorphies are presumably part of a single 

 "adaptive syndrome." Both the iguanine dentition (Hotton, 1955) and colic valves 

 (Iverson, 1980, 1982) are thought to be adaptations for a third iguanine character, 

 herbivory. However, because this correlation of form and function does not extend to all 

 herbivorous lizards, dentition, diet, and colic anatomy are here treated as separate 

 characters. 



Although Iguaninae was first used by Cope (1886), Bell (1825) is credited with 

 authorship under the principle of coordination (Article 36, third edition of the International 

 Code of Zoological Nomenclature). The content of Iguaninae as defined here differs from 

 that of Cope's (1886) Iguaninae in that the former includes Dipsosaurus and Sauromalus 

 while the latter does not. Iguaninae as defined here is identical in content to an unnamed 

 subset of Cope's (1900) more inclusive Iguaninae and to Etheridge's (1964a, 1982) 

 informal "iguanines." 



In addition to the diagnostic iguanine characters given above, acceptance of the 

 phylogenetic relationships proposed in this paper requires that the reduction or loss of the 

 ventral process of the squamosal (character 18- A) be interpreted as an iguanine 

 synapomorphy that has subsequently reversed in Amblyrhynchus and Iguana. 



In order to facilitate diagnosis of the monophyletic subgroups of iguanines, I have 

 reconstructed a hypothetical ancestral iguanine. This hypothetical ancestor has the derived 

 characters of iguanines as a whole but lacks the derived characters of its monophyletic 

 subgroups. The reason for constructing a hypothetical ancestor is that my diagnoses for 

 the monophyletic subgroups of iguanines consist exclusively of synapomorphies, while it 

 may also be useful to know what primitive features are retained by members of particular 

 monophyletic subgroups. Members of any monophyletic subgroup of iguanines possess 

 the condition found in the hypothetical ancestor unless an alternative state of the same 

 character is listed as a diagnostic synapomorphy either of the taxon in question or of a 

 larger monophyletic taxon of iguanines within which the taxon in question is included. It 

 should be kept in mind that the presence of a primitive character properly indicates only that 

 the specimen possessing it does not belong to the taxon diagnosed by the derived 

 alternative condition. It does not preclude the possibility that the specimen in question, 

 perhaps some newly discovered fossil, is not most closely related to the taxon diagnosed 

 by the derived condition. 



The hypothetical ancestral iguanine is thought to have possessed the following 

 morphological features (numbers and letters correspond with those in the list of systematic 

 characters): 



1-A. Ventral surface of premaxilla bears large posterolateral processes. 



2-A. Posteroventral crests of premaxilla small, not continuing up sides of incisive 

 process and not pierced by foramina for maxillary arteries. 



3-A. Anterior surface of premaxilla broadly convex. 



4-A. Nasal process of premaxilla slopes posteriorly. 



5-A. Nasal process of premaxilla exposed broadly between nasals. 



6-A. Nasal capsule of moderate size, nasals relatively small. 



