Higher taxonomic categories of gekkonid lizards and their evolution. Bulletin of the AMNH ; v. 135, article 1
New York : [American Museum of Natural History]
"The lizard family Gekkonidae consists of 82 genera and approximately 650 species. The family is found on the majority of land masses between latitude 50° N. and latitude 50° S. and has adapted to most environmental extremes therein. Important aspects of the general biology of these lizards are summarized for the first time. The relationships of the Gekkonidae to other modern lizards are briefly discussed, and the family is characterized in detail on the basis of internal and external morphology. It is suggested at the limbless lizards of the family Pygopodidae evolved directly from the Gekkonidae. The fossil history of gekkonoids is reviewed, and it appears that the extinct Upper Jurassic family Ardeosauridae is directly ancestral to gekkos. The Ardeosaurinae and the eublepharine gekkos have many characters in common. The Tertiary fossil gekkos Rhodanogekko, Caudurcogekko, and Gerandogekko appear to be more closely related to the Gekkoninae than to the other subfamilies as they are defined herein. These fossil genera and the Ardeosauridae are very similar to modern gekkos, which suggests an Upper Jurassic-Lower Cretaceous origin of the Gekkonidae. The most recently proposed classification of gekkonid lizards, based on the shape of the pupil, does not appear to be a natural one because of the variability of the diagnostic character. A new subfamilial classification is proposed on the basis of an examination of the morphology of all 82 recognized genera, and 283 species and subspecies, represented by nearly 1000 specimens. The following characters are used in the diagnoses: (a) true eyelids or spectacle present, (b) premaxillary bone developing from one or two centers of ossification, (c) calcified postcranial endolymphatic sacs present or absent, (d) preanal organs or escutcheon scales present, (e) ability to vocalize present or absent, (f) number of eggs laid, two or one, (g) supratemporal bone present or absent, (h) number of scleral ossicles, (i) cloacal bones and sacs present or absent, (j) angular bone present or absent, (k) splenial bone present or absent, (l) frontal bone paired or single, (m) nasal bones paired or fused, (n) parietal bones paired or fused, (o) presacral vertebrae precocious or amphicoelous, (p) morphology of the hyoid arch, (q) morphology of the second visceral arch, and (r) squamosal bone present or absent. The number of character-states of each of the 18 diagnostic characters is discussed, and the primitive or advanced condition of each state and their numerical weights are given. Possible parallelisms are also indicated. On the basis of the greatest number of shared or unshared characters and least number of parallelisms, the 82 recognized genera are grouped into four subfamilies: the Eublepharinae, the Sphaerodactylinae, the Diplodactylinae, and the Gekkoninae. The last two subfamilies bear little resemblance to the taxa of the most recently proposed classification in terms of generic composition. The relationships of the four subfamilies are expressed in the form of a phyletic dendrogram which is superimposed on a background of advancement indexes (extrapolated from the numerical weighting of the character-states). The Diplodactylinae appear to have been derived directly from the most primitive subfamily, the Eublepharinae, whereas the Gekkoninae probably evolved from a considerably more advanced form. The gekkonid subfamily Sphaerodactylinae is the most advanced, and it appears to have been derived from the evolutionary stock that gave rise to the Gekkoninae. The four generic assemblages are considered to be of equal taxonomic rank (subfamilies), unlike that proposed in the most recent classification, because of the nearly uniform increase in the total advancement index from group to group. The four taxonomic products are consistent with presently recognized zoogeographical concepts. It appears that southeastern Asia was the place of origin and early evolution of the circumglobal, now largely allopatric, Eublepharinae, and possibly all gekkonid lizards, some time during the Upper Jurassic-Lower Cretaceous. The eublepharine genus Aeluroscalabotes is restricted to this general region and appears to be the most primitive living genus of gekkos. Eublepharis is considered to be the closest living relative of Aeluroscalabotes. From the ancestral Eublepharis stock there appear to have been two separate lines of evolution within the subfamily: (1) a New World stock leading to Coleonyx, and (2) an African stock that gave rise to Holodactylus and Hemitheconyx. The magnitude of the morphological differences between the latter two genera may indicate that they did not evolve from a single ancestral Eublepharis-like population. The ancestor of Coleonyx probably arrived in the New World by way of the Bering land bridge through the continuous Paleocene Subtropical floral belt. The southern species group in Coleonyx (elegans and mitratus) appears to be more closely related to Eublepharis than is the northern group (brevis and variegatus). The occurrence of some populations of the northern group in chaparral and subtropical scrub is probably indicative of the pre-desert habitat preference of the complex. The relatively primitive Diplodactylinae are restricted to the Australian Region (today, Australia, New Caledonia and the Loyalty Islands, and New Zealand). It seems likely that the ancestral diplodactyline stock, following its origin in southeast Asia from an eublepharine ancestor, dispersed in the direction of Australia through the general region of the Indo-Australian archipelago, probably during the late Mesozoic; the Diplodactylinae are considered a member of the autochthonous fauna of the Australian Region. Concurrently, or nearly so, with the origin of the Diplodactylinae, it appears that the Gekkoninae evolved and dispersed westward through southwestern Asia toward Africa, The Gekkoninae are clearly the dominant gekkos today in terms of speciation, diversity of biology, and distribution (continuous circumglobal distribution between approximately latitude 50° N. and latitude 50° S.). Within the Gekkoninae, there appear to have been at least three levels of evolution and radiation. At least two of the earlier gekkonine radiations seem to have centered in Africa and Madagascar and southwestern Asia. The eastern part of the Paleotropical area, in contrast to the west, is dominated by 'modern expanding dominants' that belong primarily to the genera Cyrtodactylus, Gehyra, Gekko, and Lepidodactylus. The few endemic gekkonine genera of the New World do not appear to form a natural group and in most cases seem to have been independently derived from Old World ancestors, the majority of which have an African distribution today. Fortuitous trans-Atlantic rafting is postulated as the general way in which the ancestors of the gekkonine genera dispersed to the New World. The Sphaerodactylinae are restricted to the New World (primarily the Neotropical Region) and may also have been derived from an African stock, possibly near the gekkonine genus Lygodactylus and its relatives. The dominance of the sphaerodactyline gekkos in the New World may be correlated with the absence of a single major gekkonine radiation from that part of its total range"--P. 51-52.
59 p., 5 p. of plates : ill., maps ; 27 cm.
Includes bibliographical references (p. 55-59).
Includes bibliographical references (p. 55-59).