34 University of California Publications in Zoology 



B 



FIG. 13. Dorsal views of the parietals of four Iguana iguana-{A) RE 454, condylobasal length = 

 31.3mm; (B) JMS 713, 59.6mm; (C) RE 424, 71.6mm; (D) RE 489, 80.7mm-showing ontogenetic 

 change in the shape of the parietal roof. Scale equals 1 cm. 



the posterior side of the anterolateral process of the parietal. In some iguanines, this 

 overlap is much more extensive, and in others postorbital and parietal fail to contact. 

 Because variation in this feature seems to be greater within the basic taxa than between 

 them, I did not use this variation as a systematic character. 



Parietal (Figs. 5A, 6A, 13). The posteriormost bone lying on the midline of the skull 

 roof is the parietal, which is unpaired in postembryonic development. This bone forms a 

 nearly straight transverse suture with the frontal anteriorly, and meets the postorbitals and 

 postfrontals anterolaterally. It has a supratemporal process extending posterolaterally to the 

 complex articulation for the cephalic condyle of the streptostylic quadrate. The adductor 

 muscles of the jaw originate on the dorsolateral surfaces of the parietal. Their area of 

 attachment is set off by distinct crests from the medial and anterior portions of the bone, to 

 which the skin adheres. This latter area, the parietal roof, changes shape during the 

 postembryonic ontogeny of all iguanines. Changes in the shape of the parietal roof are 

 most pronounced in large species (Fig. 13), which undergo the greatest changes in size 

 after hatching. At hatching, the parietal roof is roughly trapezoidal, the lateral crests being 

 widely separated. As the animal grows, the posterior portions of the crests move 

 progressively closer together until they meet, forming a V-shaped roof. Further growth 

 results in elongation of the single median crest formed by the posterior union of the lateral 

 crests, so that the parietal roof takes on the shape of a Y with a growing leg. Different taxa 

 stop at different points along this pathway, and the point of termination is correlated with 

 size. Similar ontogenetic changes in the shape of the parietal roof have been noted in other 

 iguanids (Etheridge, 1959). 



The phylogenetic significance of differences in parietal roof shape cannot be adequately 

 assessed without a detailed allometric study, for differences in shape are complicated by 

 differences in the sizes of the organisms being compared. Furthermore, outgroup 



