On the Phylogenetic Relationship of Colubrinae, Elapidae, and Viperidae and the Evolution of Front-Fanged Venom Systems in Snakes

Phylogenetic relationships among major clades of advanced snakes and the origin of the front-fanged venom systems of elapids and viperids have been the focus of considerable study and debate during the past century, but a general consensus on the resolution of these questions has not been reached. Here we compare DNA sequences of portions of the mitochondrial small and large subunit ribosomal RNA genes for representatives of three major clades of advanced snakes: an elapid (Naja naja), a viperid (Vipera ammodytes), a colubrine (Coluber constrictor), and, for an outgroup, a boid (Boa constrictor). Phylogenetic analysis indicates a close relationship between the elapid and colubrine relative to the viperid. This finding is congruent with the immunological data of Cadle (1988). Essentially no support was found for the hypothesis of a single origin for frontfanged venom systems and sister status for viperids and elapids, as first proposed by Cope (1900). The hypothesis of a basal position for elapids, as proposed by McDowell (1986), was refuted. T WO major groups of snakes possess large, muscular, temporal venom glands and subocular venom ducts leading to front fangs. Elapidae (cobras, kraits, coral snakes, sea snakes, and their allies) constitutes one group, Viperidae (vipers and pitvipers) the other. With the possible exclusion of a small number of prob