Phylogenetic Systematics of I guanine Lizards 1 63 



Amblyrhynchus Bell 1 825 



Type species (by monotypy): Amblyrhynchus cristatus Bell 1825. 



Etymology: (Greek) Amblys, blunt, + rhynchos, snout. 



Definition: The most recent common ancestor of the populations of Recent 

 Amblyrhynchus cristatus and all of its descendants. 



Distribution: Rocky coasts of islands in the Galapagos Archipelago, Ecuador (Fig. 

 57). 



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

 following synapomorphies: 



1. Posterolateral processes on ventral surface of premaxilla absent (1-B). 



2. Anterior surface of premaxillary rostral body nearly flat (3-B). 



3. Nasal process of premaxilla nearly vertical (4-B). 



4. Nasal capsule greatly inflated; nasal bones relatively large (6-B). 



5. Frontal develops deep, paired pockets on ventral surface (1 1-B). 



6. Dorsal orbital borders wedge-shaped (12-B). 



7. Maxilla flares outward below row of supralabial foramina (15-B). 



8. Lacrimal very small (17-C). 



9. Large ventral process of squamosal (18- A). Because a reduced ventral process is 

 interpreted as a synapomorphy of Iguaninae, this is a character reversal. A similar 

 character in Iguana is interpreted as convergent. 



10. Anterodorsal surface of septomaxilla bears pronounced longitudinal crest (20-B). 



11. Parasphenoid rostrum very short (27-B). 



12. Stapes relatively thick (31-B). 



13. Dorsal edge of dentary much higher than dorsal edge of surangular on either side 

 of coronoid (32-B). 



14. Anterior inferior alveolar foramen located between coronoid and splenial; dentary 

 does not contribute to its border (34-35-C). 



15. Angular process of prearticular remains relatively small throughout ontogeny (41- 



B). 



16. Crowns of posterior marginal teeth tricuspid (46-A). This is a reversal, since the 

 presence of four or more cusps on the posterior marginal teeth is interpreted as a 

 synapomorphy of Iguanini or possibly a more inclusive group. The presence of tricuspid 

 posterior marginal teeth in adult Ctenosaura bakeri and C quinquecarinata is interpreted as 

 convergent. 



17. Secondary cusps of tricuspid marginal teeth relatively large, only slightly smaller 

 than apical cusp (47-B). 



