Phylogenetic Systematics oflguanine Lizards 77 



The number of caudal vertebrae in iguanines varies from as few as 25 in Ctenosaura 

 defensor to over 70 in Iguana iguana. Because this number varies considerably within 

 species, much of the variation is difficult to partition into character states nonarbitrarily. 

 Nevertheless, an apparent gap exists between Sauromalus and some Ctenosaura, which 

 have fewer than 40 caudal vertebrae, and all other iguanines, which have more than this 

 number. 



Outgroup comparison does not clearly indicate the plesiomorphic number of caudal 

 vertebrae in iguanines. Most outgroup species have numbers of caudal vertebrae near or 

 bridging the gap seen in iguanines. Hoplocercus is unique among outgroup taxa in having 

 a very short (fewer than 20 vertebrae), spiny tail, even more extreme than those of certain 

 Ctenosaura, and lacking any complete haemal arches. Because of this ambiguity, I used 

 the number of caudal vertebrae as a systematic character only at a level less inclusive than 

 all iguanines. 



Unlike other iguanines, Amblyrhynchus, Brachylophus, Conolophus, and Iguana 

 delicatissima lack autotomy septa along their entire caudal sequences throughout 

 postembryonic ontogeny, and thus presumably are unable to autotomize their tails. This 

 does not mean, however, that these lizards cannot regenerate their tails, for caudal 

 regeneration occurs in both Brachylophus fasciatus (Etheridge, 1967) and B. vitiensis. In 

 these cases, regeneration was associated with a broken vertebra rather than intervertebral 

 separation, supporting Etheridge's (1967) suggestion that regeneration is a function of 

 trauma to the vertebra rather than autotomy itself (but see Bellairs and Bryant, 1985). It is 

 noteworthy that all iguanines that lack caudal fracture planes are insular forms. Caudal 

 autotomy is generally thought to be an adaptation for escaping predators (Congdon et al., 

 1974; Turner et al., 1982), and the intensity of predation is often less severe on islands 

 (Carlquist, 1974). 



I am unable to resolve the polarity of this character with the four outgroups used in this 

 study. The basiliscines Laemanctus and Corytophanes, the crotaphytine Crotaphytus, and 

 the morunasaur Hoplocercus lack autotomy septa, but in other members of all of these 

 groups and in all oplurines examined, the septa are present. Thus, monophyly of each of 

 the outgroups and of iguanines requires multiple homoplastic events no matter which 

 condition, presence or absence of autotomy septa, is considered to be plesiomorphic for 

 iguanines. Because of the ambiguity involved in this character, I withheld an initial 

 decision on its polarity and used it only at a hierarchical level below that of all iguanines. 



The beginning of the second series of caudal vertebrae varies both within and among 

 iguanine species. High overlap among species in the range of this character within species 

 renders much of this variation useless as systematic characters, but one character can be 

 recognized for the purpose of comparisons among the basic taxa used in this study. In 

 Brachylophus and Dipsosaurus, the series of caudal vertebrae with two pairs of transverse 

 processes per vertebra begins at the eighth to the tenth caudal vertebra; in all other 

 iguanines, this series begins at the tenth or a more posterior vertebra. Because of 

 intraspecific variation in the beginning of this second series of caudal vertebrae, a given 



