LIZARDS, SNAKES, AND AMPHISBAENIANS FROM THE QUATERNARY SAND DUNES OFTHE MIDDLE RIO-SAO-FRANCISCO, BAHIA, BRAZIL

A Quaternary sand dune area was discovered in the morphoclimatic domai n of the semiarid Brazilian Caatinga. This site consists of high conti nental dunes located on both banks of the middle Rio Sao Francisco, Ba hia, Brazil. The area contains a very unique fauna presenting striking adaptations to psammophily and high levels of species richness and en demism. A total of 6904 specimens comprising 36 lizard (including amph isbaenians) and 25 snake species were collected at the study sites. Th is area of approximately 5000 km(2) includes 20 endemic reptiles and s everal newly described genera and species. This fauna is particularly characterized by an abundance and high diversity of fossorial and noct urnal forms differing strongly in ecological composition from Caatinga faunas and previously studied North American, Kalaharian, and Austral ian desert faunas. These differences may be a result of an association of an ecogeographic mechanism of speciation initially synchronic and latter replaced by a classic allopatric speciation which occurred in a n ancestral Caatinga fauna. It is postulated that the last event of sp eciation possibly took place when the Sao Francisco river attained ful l exorrheism dividing formally continous sands and isolating ancestral psammophilic populations on opposite banks. At present, four closely related species pairs isolated by the river support this model. The la st period of species differentiation most likely corresponded to the e nd of Wurm-Wisconsin glacial period.