1 64 University of California Publications in Zoology 



18. Second ceratobranchials of hyoid apparatus separated from one another medially 

 for most or all of their lengths (54-B). This character occurs also in Sauromalus, in which 

 it is interpreted as convergent. 



19. Scapular fenestrae small or absent (65-B). This character occurs also in 

 Sauromalus, in which it is interpreted as convergent. 



20. Posterior process of interclavicle does not extend beyond lateral comers of sternum 

 (68-B). This character occurs also in Sauromalus, in which it is interpreted as convergent. 



21. Lateral processes of interclavicle form angles of between 75° and 90° with the 

 posterior process; interclavicle roughly T-shaped (69-B). This character also occurs in 

 Sauromalus, in which it is interpreted as convergent. 



22. Sternal fontanelle small or absent (70-B). This character also occurs in 

 Sauromalus, in which it is interpreted as convergent. 



23. Xiphistema separated from one another medially (71-B). The xiphisterna of 

 Sauromalus are also separated medially but to a much greater extent. I consider this 

 similarity to be convergent. 



24. Separable skull osteoderms develop over frontal, prefrontal, and nasal bones (74- 

 B). 



25. Colic wall without valves but with numerous irregular transverse folds (79-B). 



26. Superciliary scales quadrangular and nonoverlapping (84- A). This character also 

 occurs in Sauromalus, in which it is interpreted as convergent. 



27. Gular fold weakly developed (87-B). 



28. Digits of manus and pes partially webbed (93-B). 



Other possible synapomorphies of Amblyrhynchus are a laterally compressed tail 

 (Tracy and Christian, 1985) and a high rate of tooth replacement associated with wide 

 alveolar margins of the maxilla, premaxilla, and dentary. 



In addition, the following derived character occurs in some Amblyrhynchus: 

 Infraorbital foramen located entirely within palatine bone (24-B). This character occurs 

 also in Brachylophus and in some Ctenosaura and Sauromalus. 



Fossil record: None. 



Comments: Monophyly of Amblyrhynchus is the best- supported phylogenetic 

 hypothesis within Iguaninae. Sauromalus has almost as many characters that are 

 interpreted as synapomorphies, but it has more that require convergence elsewhere within 

 iguanines and, in this sense, are ambiguous. In terms of a simple tally of derived 

 characters used in this study, Amblyrhynchus is the most highly modified iguanine relative 

 to the most recent common ancestor of them all. Amblyrhynchus not only possess 

 numerous synapomorphies supporting its own monophyly, but also possesses those of 

 Amblyrhynchina and Iguanini. This high degree of morphological modification is not 

 surprising, given the unique natural history of these animals; Amblyrhynchus are the only 

 extant lizards that gain a major part of their sustenance from the sea (Darwin, 1835; Heller, 

 1903; Carpenter, 1966; Dawson et al., 1977; Dee Boersma, 1983). Many of the unique 



