COLUBROID SYSTEMATICS: EVIDENCE FOR AN EARLY APPEARANCE OF THE VENOM APPARATUS FOLLOWED BY EXTENSIVE EVOLUTIONARY TINKERING

Abstract

Colubroids or advanced snakes form a monophyletic group comprising four families: Atractaspididae (11 genera, 70 species), “Colubridae” (300 genera, 1850 species), Elapidae (65 genera, 270 species) and Viperidae (33 genera, 240 species). A preliminary classification of colubroids based both on morphological and molecular data is presented and all extant genera of “Colubridae” are listed accordingly. The front-fanged venom system (displayed by some Atractaspididae, all Elapidae and all Viperidae) evolved several times independently and appeared early within colubroids. The rear-fanged venom system (displayed by some Atractaspididae and many “Colubridae”) has been studied less than the front-fanged system, although it is clear that opisthoglyph “Colubridae” constitute a polyphyletic group. The other components of the venom apparatus, the glands and the secretions, also show great variability, rendering the reconstruction of the evolutionary history of the venom apparatus difficult. Nevertheless, the presence of serous secretory cells in the supralabial region and of a differentiated maxillary dentition within the most basal extant lineages of advanced snakes strongly suggest that the venom apparatus is a synapomorphy of the Colubroidea and that its absence in a few “Colubridae” results from secondary losses.