1 42 University of California Publications in Zoology 



Diagnosis: Members of this taxon can be distinguished from other iguanines by the 

 following synapomorphies (here and afterwards the parenthetical numbers and letters 

 correspond with those in the list of systematic characters): 



1. Large, paired openings at or near frontonasal suture present (9-B). 



2. Parietal foramen located entirely within frontal bone (13-C). This character occurs 

 also in Cyclura carinata and variably in some Ctenosaura, Sauromalus, and other Cyclura. 



3. Lateral process of palatine behind infraorbital foramen small or absent (22-B). 



4. Medial borders of pterygoids curve sharply toward midline anterior to pterygoid 

 notch; pyriform recess narrows abruptly (25-B). This character occurs in all other 

 iguanines except Brachylophus and may thus be a synapomorphy of Iguaninae that has 

 reversed in Brachylophus. 



5. Lateral pointed processes on cristae interfenestralis present (30-B). 



6. Posterior ends of lateral and medial crests of retroarticular process diverge 

 ontogenetically, so that outline of retroarticular process is quadrangular in large specimens 

 (42-B). 



7. Crowns of posterior marginal teeth with four cusps (46-B). An increase in tooth 

 cuspation characterizes all other iguanines except Amblyrhynchus and some Brachylophus 

 and Ctenosaura; therefore this character may be a synapomorphy of a more inclusive group 

 that has reversed in certain taxa. 



8. Pterygoid teeth usually absent (50-B, 51-B), This character also occurs in 

 Conolophus. When present, the pterygoid teeth of Dipsosaurus lie along the medial edge 

 of the pterygoid, while those of Conolophus lie more laterally, supporting the conclusion 

 that the absence of pterygoid teeth in these two taxa is convergent. 



9. Colon with one or more circular valves (80-B). This condition occurs also in all 

 other iguanines except Brachylophus and may be a synapomorphy of a more inclusive 

 group. 



10. Superciliary scales greatly elongate and strongly overlapping (84-C). The derived 

 status of this character is questionable. 



11. One subocular scale much longer than others (85-C). The derived status of this 

 character is questionable. 



Fossil record: Olson (1937) described Tetralophosaurus minutus based on a fragment 

 of a lower jaw from Lower Miocene deposits in Nebraska. The specimen was referred to 

 Dipsosaurus by Estes (1983), who stated that it was indistinguishable from D. dorsalis, but 

 this conclusion is based on overall similarity. Almost complete skulls and dentaries from 

 the PUocene of southern California have been referred to Dipsosaurus by Norell (1983). 



Comments: Failure of the lateral palatine process to contact the jugal behind the 

 infraorbital foramen (character 23) suggests that Dipsosaurus is the sister group of all other 

 iguanines. However, the gently curving medial pterygoid borders and wide pyriform 

 recess of Brachylophus (character 25) suggest that this taxon, rather than Dipsosaurus, is 



