Phylogenetic Systematics oflguanine Lizards 89 



Another unique feature occurs in some Sauromalus, notably S. varius. In these 

 animals the ischium is excavated mesial to the posteriorly directed ischiac tubercle, 

 enhancing the distinctness of this structure. Because this character varies within a single 

 genus, it is uninformative about relationships among the basic taxa used in this study. 



I disagree with Lazell's (1973:1-2) statement that "In Dipsosaurus and Sauromalus the 

 ilial shaft tapers abruptly posteriorly and the anterior iliac process is rather weakly 

 developed." The ilial shaft of Sauromalus is narrower at its posterior terminus than those 

 of other iguanines, but it does not taper abruptly. In Dipsosaurus the ilial shaft may taper 

 abruptly, but it is broad near its posterior end like that of other iguanines except 

 Sauromalus. While the anterior iliac process of Sauromalus does appear to be relatively 

 small, that of Dipsosaurus is not. 



LIMBS 



Iguanine hmbs exhibit considerable variation, but I have chosen not to use this variation as 

 the basis for systematic characters. All iguanines possess the same bony elements in their 

 limbs, but the proportions of the various limb bones vary considerably among iguanine 

 taxa. Nevertheless, these proportions seem to be very plastic features, so plastic that I was 

 unable to establish polarities with any confidence. Therefore, I give only a general 

 description of this variation and devote most of the section to the description of characters 

 that do not vary among iguanines but that may be useful at higher levels of comparison. 



Compared to those of other iguanines, the limb bones of Brachylophus are relatively 

 long, while those of Amblyrhynchus and Sauromalus are relatively short. These 

 proportional differences are most evident in the long bones, metapodials, and phalanges. 

 Proportional differences in the carpal and tarsal elements (mesopodials) are less obvious. 



All iguanines possess the following bones in the forelimb (Fig. 42): humerus, radius, 

 ulna, radiale, ulnare, pisiform, lateral centrale, five distal carpals, five metacarpals, and 17 

 phalanges. According to Carroll (1977), the first distal carpal of modem lizards is 

 homologous with the medial centrale of other diapsids. As in other iguanids (Renous- 

 Lecuru, 1973), the intermedium is absent. The phalangeal formula of the manus is 

 2:3:4:5:3. An entepicondylar foramen is present in the humerus. 



The hind limbs of iguanines (Figs. 43, 44) consist of femur, tibia, fibula, 

 astragalocalcaneum, two distal tarsals proximal to metatarsals three and four, five 

 metatarsals, and 18 phalanges. The phalangeal formula of the pes is 2:3:4:5:4 which, like 

 that of the manus, is presumably plesiomorphic for squamates. 



OSTEODERMS 



Two large Amblyrhynchus (JMS 126, 127) have dermal ossifications that apparently 

 formed within the large, conical scales overlying the nasal, prefrontal, and frontal bones 

 (PI. 1), confirming Camp's (1923:307) observation that osteoderms are present in this 

 taxon. Osteoderms, which differ from the rugosities that develop on various bones of the 



