Phylo genetic Systematics of I guanine Lizards 3 3 



skull roof in the vicinity of the frontoparietal suture ossifies in postembryonic ontogeny, 

 the location of the parietal foramen cannot always be determined in young specimens. 



In Amblyrhynchus, Brachylophus, Conolophus, and Iguana, some species of 

 Ctenosaura, and most species of Cyclura, this foramen almost always lies within the 

 frontoparietal suture, though it may notch either frontal or parietal more than the other. The 

 parietal foramen is entirely within the frontal in Cyclura carinata and Dipsosaurus; a suture 

 connecting it with the frontoparietal suture is usually present in the former but usually 

 absent in the latter. The single skull of Ctenosaura defensor examined has the parietal 

 foramen located entirely within the frontal. All species of Sauromalus and several species 

 of Ctenosaura are variable in this character: the parietal foramen in these taxa is commonly 

 found both at the suture between frontal and parietal or entirely within the frontal. 



Most members of the outgroups examined in this study have the parietal foramen at the 

 frontoparietal suture, suggesting that this condition is plesiomorphic for iguanines. 

 Exceptions are Basiliscus and Corytophanes, which have the parietal foramen entirely 

 within the frontal; Laemanctus, in which the parietal foramen may be either on the 

 frontoparietal suture or within the frontal; and Morunasaurus annularis, in which the 

 parietal foramen appears to be absent. Assuming that fixation of an apomorphic feature is 

 more readily achieved through a polymorphic intermediate condition, I recognized the 

 variable condition as the intermediate stage in a three-state transformation series. 



Postfrontals (Figs. 5 A, 6A). The postfrontals are small bones confined to the 

 posterodorsal margins of the orbits. The posterior surface of each postfrontal is sutured 

 medially to the frontal and laterally to the postorbital. The postfrontal is invariably present 

 as a discrete element in iguanines, morunasaurs, and Laemanctus; it is indistinct (absent or 

 fused) in crotaphytines, oplurines (rarely, a small separate bone is present), and the 

 basiliscines Corytophanes and Basiliscus. 



In iguanines, the lateral portion of the postfrontal may form part of a bony knob along 

 with the postorbital (Figs. 6A), which serves as an attachment point for the skin (Oelrich, 

 1956). The relative development of this knob varies among iguanine genera. 

 Amblyrhynchus and Brachylophus have moderate-sized knobs directed mostly laterally. 

 The knob is small or absent in Conolophus, Ctenosaura, Dipsosaurus, and Sauromalus. 

 Iguana and especially Cyclura have large, anteriorly directed knobs (Fig. 9A). The relative 

 size of the postfrontal-postorbital knob increases with increasing body size, making it 

 difficult to compare those of animals differing gready in body size. Because of this 

 problem, I have chosen not to use the variation in the development of this knob as a 

 systematic character. 



Postorbitals (Figs. 5A, 6A). The postorbitals of iguanines are paired, triradiate bones 

 situated on the posterolateral sides of the skull just behind the orbits. Their lateral surfaces 

 are often slightly concave. Like those of all iguanians, the postorbitals of iguanines form a 

 major part of the postorbital bar and articulate anteroventrally with the jugals and 

 posteroventrally with the squamosals. Preliminary examination suggested that the 

 relationship of postfrontal to parietal might be a useful systematic character. The 

 postorbital generally ends medially where it contacts the parietal, or it may slightly overlap 



