Phylogenetic Systematics of I guanine Lizards 173 



Barbuda may also be remains of Cyclura (Pregill, 1981; see section on the fossil record of 

 Conolophus, above). 



Comments: Cyclura is often assumed to be closely related to Ctenosaura (Barbour and 

 Noble, 1916; Bailey, 1928; Schwartz and Carey, 1977), which it resembles in general 

 body form, terrestrial habits, and the verticils of enlarged, spinous caudal scales. These 

 similarities were noticed at least as early as Harlan (1824), who erected Cyclura for species 

 that are now placed in both Cyclura (carinata) and Ctenosaura (teres = acanthura). Despite 

 the resemblance between Ctenosaura and Cyclura, Cyclura probably shared a more recent 

 common ancestor with Iguana than it did with Ctenosaura. The similarities between 

 Cyclura and Ctenosaura in general body form and terrestriality probably represent primitive 

 features retained from the common ancestor of all three taxa; and since not all Cyclura 

 possess the verticils of enlarged, spinous caudal scales, some form of homoplasy in tail 

 morphology is required no matter which relationships are accepted. Furthermore, Cyclura 

 and Iguana share at least three derived characters not seen in Ctenosaura: abutment of the 

 squamosal against the dorsal end of the tympanic crest of the quadrate (19-B); a wide 

 parabasisphenoid (28-B,-C); and highly cuspate posterior marginal teeth (46-C,-D). 

 Although the last character occurs also in Ctenosaura defensor, my analysis of relationships 

 within Ctenosaura indicates that this is convergent. 



In addition to the characters suggesting a close phylogenetic relationship between 

 Iguana and Cyclura, there are other characters suggesting that Iguana is actually a subgroup 

 of Cyclura, as defined here. In other words, there are characters suggesting that the most 

 recent common ancestor of all Cyclura was also an ancestor of Iguana. Iguana shares 

 derived features of the cephalic scutellation, such as the enlarged snout scales and the row 

 of enlarged sublabials, as well as a derived widening of the parabasisphenoid with some, 

 but not all, species of Cyclura. There is a particularly close resemblance between Cyclura 

 cychlura and Iguana delicatissima in these features. Nevertheless, the toe combs, the 

 verticils of enlarged, spinous caudal scales, and the high number of premaxillary teeth are 

 derived features seen in Cyclura but not in Iguana. The morphology of the posterior 

 marginal teeth also varies within Cyclura, with some approaching the highly cuspate 

 morphology seen in Iguana much more closely than others. However, the high degree of 

 variation in this character, at least some of which is ontogenetic, along with small samples 

 and ambiguities caused by wear, prevent me from making any definite statement about the 

 relationships suggested by this character. 



In any case, the precise relationships between Iguana and Cyclura are unclear, because 

 the distributions of derived characters among taxa contradict one another. I provisionally 

 accept the monophyly of Cyclura, but consider the issue to be in need of further study. If 

 the most recent common ancestor of all Cyclura was also an ancestor of Iguana, then, 

 according to the phylogenetic definitions of taxa adopted here. Iguana is a subgroup of 

 Cyclura rather than a separate taxon, and Iguanina is a synonym of Cyclura. 



