74 University of California Publications in Zoology 



neural spine height. Crotaphytines, Hoplocercus, Chalarodon, and some Opiums have 

 short neural spines; those of Laemanctus, Morunasaurus, and other Oplurus are roughly 

 intermediate; and those of Basiliscus, Corytophanes, and Enyalioides are tall, reaching 

 extreme heights in adult male Basiliscus. Because of this ambiguous evidence, I did not 

 use neural spine height as a character at the first level of phylogenetic analysis within 

 iguanines, though it was used later at a lower hierarchical level. 



The zygosphenes oi Dipsosaurus differ from those of other iguanines (Fig. 36). In this 

 taxon, the articular surfaces of the zygosphenes are connected laterally to those of the 

 prezygapophyses by a continuous arc of bone (Fig. 36A). All other iguanines have a deep 

 anterior notch separating the articular surfaces of the zygosphenes from those of the 

 prezygapophyses (Fig. 36B). 



In their weakest form, zygosphenes are mere out-tumings of the medial surfaces of the 

 prezygapophysial facets that face dorsolaterally (Hoffstetter and Gasc, 1969). When more 

 strongly developed, the articular surfaces of the zygosphenes are oriented laterally or 

 ventrolaterally, eventually coming to face directly opposite those of the prezygapophyses. 

 The final stage in the expression of the zygosphenal half of the accessory vertebral 

 articulation appears to be the separation of the zygosphenes from the prezygapophyses by a 

 notch. Thus, Dipsosaurus is the only iguanine that does not exhibit full development of the 

 zygospheneal articulations. Although the degree to which the zygosphene-zygantrum 

 articulation is developed may be positively correlated with size in iguanids (Etheridge, 

 1964a), this fact alone cannot account for its relatively weak development in Dipsosaurus, 

 the smallest iguanine. Outside of Iguaninae, Corytophanes, which is about the same size 

 (snout-vent length) as Dipsosaurus, possesses the deep notch separating zygosphenes from 

 prezygapophyses, while Petrosaurus that are larger than Dipsosaurus do not. 



Outgroup comparison provides equivocal evidence concerning the plesiomorphic 

 zygosphenal morphology for iguanines. Among the outgroups examined in this study, the 

 vertebrae of basiliscines and some Enyalioides resemble those of most iguanines in having 

 strongly developed zygosphenes and zygantra with deep anterior notches between the 

 articular surfaces of the zygosphenes and those of the prezygapophyses. Crotaphytines 

 and most morunasaurs have weakly developed accessory vertebral articulations: the 

 articular surfaces of the zygosphenes are continuous with the medial portions of those of 

 the prezygapophyses, and, unlike those of all iguanines, they face dorsolaterally rather than 

 ventrolaterally. The zygosphene-zygantrum articulations are very weakly developed in 

 Oplurus and Chalarodon. Therefore, some nonhomology between morphologically similar 

 vertebrae is required under the assumption of iguanine monophyly. Either the notch in the 

 basiliscine accessory articulation (and that of some Enyalioides) is convergent with the one 

 in iguanines, or its absence in Dipsosaurus is convergent (and possibly also a reversal) 

 with a similar condition seen in other outgroups. 



Sacrum (Fig. 39). Like all tetrapodous squamates, iguanines characteristically have 

 two sacral vertebrae, although some specimens have asymmetrical sacra of the form 

 reported by Hoffstetter and Gasc (1969) involving three vertebrae (Table 4). I recognize 



