GECKO CLASSIFICATION 



119 



unable to modify pupil shape and instead regulate light through 

 absorbance by crystallins in the lens. Although Roll and Schwemer 

 ( 1999) assumed that the use of particular crystallins was likely to 

 have evolved only once, there is no evidence that all diurnal gekkonids 

 are allied (e.g. Phelsuma + Lygodactyhts and Sphaerodactylus + 

 Quedenfeltia + Narudasia + Saurodactylus; Kluge and Nussbaum 

 1995). This avenue of approach, however, suggests that at the 

 anatomical and molecular level, data from the visual system may yet 

 be of significance in assisting in the resolution of pattern between 

 nocturnal and secondarily diurnal clusters of gekkonids (including 

 sphaerodactyls). 



Despite attempts to move away from digital architecture as a 

 primary means of identifying suprageneric clusters, this has contin- 

 ued to play a role and has been instrumental, by way of examination 

 of internal architecture, in assisting in the circumscription of a 

 number of apparently monophyletic assemblages (Russell, 1976). 

 Pedal anatomy remains a primary determinant of generic allocation 

 and a major clue to potential higher order relationships (e.g., 

 Nussbaum and Raxworthy 1994). 



Changes in generic alignment and more modern views of plate 

 tectonics have necessitated a rethinking of Underwood's (1954) 

 biogeographic hypotheses. Essentially the eublepharids appear to 

 represent an ancient Laurasian radiation, in keeping with Under- 

 wood's (1954) ideas. The remaining gekkotans are now regarded as 

 being of Gondwanan origin and to consist of an essentially east 

 Gondwanan diplodactylid radiation and a west Gondwanan gekkonid 

 radiation, with the latter having given rise, in turn, to the New World 

 sphaerodactyls. 



Interpretation of patterns of relationship must now deal with the 

 recognition that the age of the Gekkota is much greater than was 

 believed in 1954 and that many genera might be quite ancient. 

 Hence, generic body plans may have been established for very long 

 periods, making them rather discrete from one another and render- 

 ing it difficult to erect hypotheses of relationship. Even among the 

 sphaerodacyls. generic differentiation is estimated to have occurred 

 as much as 40 million years ago (Hass 1 99 1 ). King ( 1 987a, 1 987b), 

 on the basis of chromosomal and immunological data correlated 

 with tectonic history of the Australian region, estimated a minimum 

 divergence of 66 my between the two major clades of diplodactylines, 

 and at least 120 my for the origin of the gekkotans. 



Despite the magnitude of the problem, only patterns of relationship 

 within the rather amorphous Gekkonidae ( Underwood's Gekkoninae) 

 remain relatively unassailed. Even here, however, large, circumglobal 

 unwieldy genera have been broken into smaller, more geographically 

 circumscribed taxa and there is now an opportunity to begin to make 

 inroads into the determination of the patterns of interrelationship of 

 suprageneric clusters of gekkonid taxa. This may best be broached by 

 taking exemplars, appropriately selected (Bininda-Emonds et al. 

 1998) from the putative clusters and the enigmatic genera, and 

 investigating a combination of morphological and molecular data. 

 Given the magnitude of the problem, this will be an iterative process 

 and will necessitate frequent cross-checking within and between 

 clusters. The boldness of Garth Underwood's approach will have to 

 be adopted in selecting novel sources of data to allow new approaches 

 to be taken and insights to be revealed. 



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