Although the Neotropics are recognized as a region of high biodiversity, mainland Neotropical gekkotans are a notable exception to this rule. There are comparatively few species, representing a number of disparate genera (Abdala and Moro, 1996) with independent evolutionary origins, distributions, and histories (Vanzolini, 1968). This is surprising given the high worldwide gekkonid diversity of over 600 species (Kluge, 2001). The turnip-tailed gecko, Thecadactylus rapicauda (Houttuyn, 1782), demonstrates this low diversity as the only nocturnal, arboreal lizard over much of its range (Vitt and Zani, 1997). Considering its ostensible monotypy, T. rapicauda has one of the most extensive ranges of any lizard (Mattison, 1989), occurring from Yucatan to Bolivia, throughout the Amazon Basin, east to the Guyanan region, and on the Lesser Antilles (Fig. 1; Russell and Bauer, 2002). Based on morphology, Burt and Myers (1942) postulated that the taxon might be split into multiple entities in the future and Mijares-Urrutia and Arends (2000) suggested that the karyotypes of specimens from diVerent populations diVer. Whether T. rapicauda represents a single cohesive species or multiple distinct species is of considerable