Phylogenetic Systematics oflguanine Lizards 59 



Dipsosaurus, but in this taxon the posterior ends of the crests move apart during ontogeny 

 so that the retroarticular process of large Dipsosaurus is quadrangular (Fig. 29). 



Most outgroups have a triangular retroarticular process, much like those seen in the 

 majority of iguanines; however, I have observed quadrangular retroarticular processes in 

 Morunasaurus annularis and Enyalioides praestabilis. Thus, either the quadrangular 

 retroarticular process of Dipsosaurus is apomorphic or the polarity of this character is 

 equivocal, but a quadrangular retroarticular process will never be considered to be 

 plesiomorphic with the outgroups used in this study. 



The medial crest of the retroarticular process varies in size within Iguaninae. In 

 Amblyrhynchus (Fig. 28D-F), Brachylophus, Conolophus, and Cyclura cornuta, this 

 structure is but a low, rounded ridge, contrasting with the sharp crest seen in other 

 iguanines (Figs. 28A-C, 29). Intraspecific variability in Amblyrhynchus and Conolophus, 

 but more important, variation within basiliscines, morunasaurs, and oplurines, prevented 

 me from using the size of the medial crest as a character for phylogenetic analysis. 



Articular (Figs. 6C, 28, 29). The articular bone is the ossified posterior end of 

 Meckel's cartilage and forms the condyle that articulates with the quadrate of the skull 

 proper. It sits in a groove in the dorsal surface of the jaw between the prearticular 

 posteriorly and medially and the surangular anterolaterally. The articular of iguanines fuses 

 to the prearticular around the time of hatching. I have not studied variation in the iguanine 

 articular. 



MISCELLANEOUS HEAD SKELETON 



Marginal Teeth (Figs. 5B, 8, 30). The marginal teeth of iguanines exhibit a bewildering 

 diversity of form and could easily be the subject of a study by themselves. Some 

 dentitional features common to all iguanines are pleurodonty and the formation of 

 replacement teeth directly lingual to the teeth being replaced (iguanid tooth-replacement 

 pattern of Edmund, 1960). Although lizards are often stereotyped as being homodont, all 

 iguanines exhibit some regional differentiation in the morphology of their marginal teeth. 

 This differentiation is most pronounced, at least in terms of crown morphology, in Cyclura 

 and Sauromalus, where the crowns of the anterior teeth are conical and usually lack lateral 

 cusps while those of the posterior teeth are laterally compressed and polycuspate. Another 

 feature common to all iguanines is an allometric increase in tooth number within species, a 

 feature that has been reported previously in iguanines (Ray, 1965; Montanucci, 1968) and 

 in various other iguanids (Etheridge, 1962, 1964b, 1965a; Ray, 1965). This allometric 

 increase in tooth number results from the addition of teeth to the posterior ends of the 

 maxillary and dentary tooth rows; the number of premaxillary teeth remains constant. 



Variation in the number of premaxillary teeth of iguanines is given in Table 3. Most or 

 all species of Amblyrhynchus, Brachylophus, Conolophus, Ctenosaura, Dipsosaurus, and 

 Iguana have a statistical mode of seven premaxillary teeth. The species of Cyclura 

 generally have modes of greater than seven premaxillary teeth, and those of Sauromalus 

 have modal numbers lower than seven. Ctenosaura defensor also has fewer than seven 



