Phylogenetic Systematics oflguanine Lizards 49 



interfenestralis. Although this process is absent or very small in basiliscines, 

 crotaphytines, morunasaurs, and oplurines, it is present in some sceloporines. I consider 

 Dipsosaurus and these sceloporines to have developed a pointed process on the crista 

 interfenestralis convergently. 



Stapes. The stapes, or columella, is a sound-transmitting bone that extends from the 

 fenestra ovalis (foramen ovale of Oelrich, 1956) in the braincase to a point just behind the 

 posterior crest of the quadrate. In Ufe it is attached to the external tympanic membrane via a 

 cartilaginous extracolumella, which is often damaged during skeletal preparation. The 

 stapes of Amblyrhynchus is robust compared to those of all other iguanines and most other 

 iguanids, although some sceloporines also have a thick stapes (Axtell, 1958; Earle, 1962). 



MANDIBLE 



There are seven bones present in the mandibles of all iguanines (Fig. 6B,C); from anterior 

 to posterior these are: dentary, splenial, coronoid, angular, surangular, prearticular, and 

 articular. The articular is a splanchnocranial endochondral bone; the remaining bones are 

 dermal. In some noniguanine iguanids, either splenial or both splenial and angular may be 

 absent (Etheridge and de Queiroz, 1988). 



Dentary (Figs. 6B,C, 22). The dentary is the anteriormost bone in the mandible and 

 extends posteriorly to about the level of the apex of the coronoid. It is the only tooth- 

 bearing bone in the lower jaw. Anterior to the splenial, Meckel's cartilage, which extends 

 from the articular bone to the anterior end of the mandible, is completely enclosed in a bony 

 tube formed by the dentary. In some other iguanids (e.g., morunasaurs) the groove for 

 Meckel's cartilage is completely open lingually, while in others (e.g., crotaphytines) the 

 dorsal and ventral edges of the groove meet to close the tube but remain separated by a 

 suture. In one late embryo of Amblyrhynchus (SDNHM 45156), Meckel's groove is 

 closed but retains a suture; however, in all postembryonic iguanines the upper and lower 

 dentary portions of Meckel's groove are closed and fused. 



A series of mental foramina are positioned along the labial face of the anterior half of 

 the dentary. In all iguanines except Amblyrhynchus and in all outgroups examined, these 

 foramina lie in a line about halfway between the dorsal and ventral edges of the dentary, 

 and the dorsal edge of the dentary where it meets the coronoid is approximately level with 

 the dorsal border of the surangular just posterior to the coronoid (Fig. 22A). The dorsal 

 border of the dentary in Amblyrhynchus is high, well above the level of the dorsal border 

 of the surangular, and the row of mental foramina lies more than halfway down the labial 

 surface of the dentary (Fig. 22B). 



Splenial (Fig. 6B,C, 23). The exposed portion of the splenial is roughly diamond- 

 shaped and lies on the lingual face of the mandible wedged into the posterior end of the 

 dentary. Posterodorsally, the splenial contacts the coronoid and the surangular; 

 posteroventrally it is bounded by the angular. The relative size of the splenial is variable in 

 iguanines, with that of Sauromalus being smaller than those of the other genera. Although 

 there is considerable variation in the size of the splenial among the four outgroups used in 



