Phylogenetic Systematics oflguanine Lizards 85 



posterior process of the interclavicle extends beyond this level (Fig. 40B) and, depending 

 on the taxon, it may extend beyond the points of attachment of the second or even the third 

 sternal-rib pairs. Conolophus pallidus and Cyclura nubila have interclavicles of 

 intermediate length. In these taxa the interclavicle extends to about the level of the lateral 

 comers of the sternum or slightly beyond. The width of the posterior process appears to be 

 related to its posterior extent: short interclavicles are usually wider than long ones. The 

 correlation is not strict, however, for some Sauromalus have narrow posterior processes. 



Among the outgroups examined, only some Crotaphytm have an interclavicle that does 

 not extend posteriorly beyond the lateral comers of the sternum. I therefore considered the 

 short interclavicle to be apomorphic for iguanines. 



Another variable feature of iguanine interclavicles is the angle between each lateral 

 process and the posterior process. All species exhibit at least 10° of variation in this feature 

 with significant intertaxic overlap. For this reason I recognize only two categories as 

 character states. Amblyrhynchus and Sauromalus (Fig. 40C) have roughly T-shaped 

 interclavicles, with the angle between the lateral and posterior processes ranging from 75° 

 to 90°. Other iguanines have arrow-shaped interclavicles (Fig. 40B); the angle formed by 

 the lateral and posterior processes is usually less than 75°. Although the angle in question 

 overlaps the first category in some members of both species of Brachylophus and 

 Conolophus, as well as in some Cyclura nubila, the lower limits of the range of angles in 

 these species is well below that in Amblyrhynchus and Sauromalus. Outgroup comparison 

 indicates that the arrow-shaped interclavicle is plesiomorphic. Among basiliscines, 

 crotaphytines, morunasaurs, and oplurines, I have found T-shaped interclavicles only in 

 the basiliscines Laemanctus serratus and Corytophanes hernandesii. 



Sternum and Xiphisterna (Figs. 37, 40). The sternum of iguanines is shaped like a 

 diamond or a pentagon and is composed of calcified cartilage. In embryos and some 

 hatchlings, the sternal plate is paired, but the two halves fuse in late embryonic or early 

 postembryonic ontogeny to form a single median element. Anterolaterally, the sternum 

 meets the epicoracoids in a tongue-in-groove articulation, the coracostemal joint, which 

 permits posterolateral- anteromedial movements of the scapulocoracoid units relative to the 

 sternum (Jenkins and Goslow, 1983). The posterolateral borders of the sternal plate are 

 the attachment sites for the cartilaginous ventral portions of four thoracic rib pairs (sternal 

 ribs) and two others that attach via the xiphistema. A sternal fontanelle may be present 

 (Fig. 40B) or absent (Fig. 40C). 



In most iguanines, the sternal fontanelle is long and narrow and is covered partially or 

 completely by the posterior process of the interclavicle. In Amblyrhynchus and 

 Sauromalus the sternal fontanelle is often small, and in the latter it may be subdivided into 

 two or three small, round holes. In some specimens of both taxa the fontanelle is absent. 

 Absence or small size of the sternal fontanelle is unequivocally apomorphic on the basis of 

 the outgroups used in this study. 



Sternal shape is variable in iguanines and is partly related to another feature, the 

 proximity of the two sternal-xiphistemal attachments to one another and the midline. In 

 most iguanines the xiphistema attach to the sternum very close to the midline and to one 



