136 University of California Publications in Zoology 



Paradipsosaurus mexicanus. Fries et al. (1955:15) stated that this animal "would appear to 

 approach more closely to the northern crested lizard Dipsosaurus than to any of the other 

 iguanids that presently live in Mexico and the southwestern United States." However, the 

 similarities they cite (broad, flat parietal table elevated well above level of supratemporal 

 arch; unrestricted supratemporal fossa; deep, broad snout without pronounced 

 nasolachrymal ridges; forward opening nares), provide no evidence for a close relationship 

 to Dipsosaurus, since they are all plesiomorphic for Iguania. Of the five diagnostic 

 iguanine synapomorphies identified in this study, only the morphology of the tooth crowns 

 can be assessed in Paradipsosaurus. Unlike the teeth of iguanines, those of 

 Paradipsosaurus are said to be a little dilated and noncuspidate (Fries et al., 1955). 

 Furthermore, while all postembryonic iguanines and various other iguanids have a 

 relatively small splenial and have the dentary portion of Meckel's groove closed and fused, 

 both derived features within Iguania, the splenial of Paradipsosaurus is relatively large and 

 Meckel's groove is open (Estes, 1983). Therefore, although Paradipsosaurus and 

 Dipsosaurus share the derived condition of having the parietal foramen located within the 

 frontal bone, this similarity is convergent, since Paradipsosaurus is not an iguanine. Estes 

 (1983) reached similar conclusions concerning the relationships of this fossil. 



Gilmore (1928) described Parasauromalus olseni based on a fragment of a right dentary 

 from the Eocene of Wyoming. Although he did not specifically propose that it was related 

 to the iguanine Sauromalus, Gilmore considered the teeth of the fossil to resemble those of 

 Sauromalus ater most closely, made his comparisons with this species only, and named the 

 fossil as if to suggest a close relationship with Sauromalus (para means near). If new 

 material has been correctly referred to Parasauromalus (Estes, 1983), then this taxon is not 

 an iguanine and therefore cannot be closely related to Sauromalus. Contrary to Gilmore's 

 (1928) statements, the tooth crowns oi Parasauromalus are not particularly similar to those 

 oi Sauromalus. They are only slightly flared and tricuspid (Estes, 1983), while those of 

 Sauromalus are strongly flared and polycuspate. The supratemporal of Parasauromalus lies 

 on the lateral surface of the supratemporal process of the parietal (figured by Estes, 1983), 

 whereas the supratemporal of iguanines lies in a derived position on the medial surface. 

 The splenial of Parasauromalus is relatively large and the Meckelian groove closed but 

 unfused (Estes, 1983), primitive iguanian characters not retained by any iguanine. 



The oldest fossils referred to Iguaninae for which this reference cannot be rejected are 

 Lower Miocene in age: Tetralophosaurus (Olson, 1937), a fragment of a lower jaw from 

 Nebraska referred to Dipsosaurus by Estes (1983); a fragment of a lower jaw and a sacral 

 vertebra from Florida (Estes, 1963); and another fragment of a lower jaw from Texas, 

 referred to either Ctenosaura or Sauromalus by Stevens (1977). Because of their 

 fragmentary nature, these specimens are not definitely referable to Iguaninae on the basis of 

 synapomorphies. The oldest fossil that is clearly iguanine is a nearly complete skull from 

 the Pliocene of southern California (Norell, 1983). These and other fossil records are 

 given under the least inclusive taxon to which they belong or are most closely related. 



