An evolutionary hypothesis of snake fangs

One hypothesis for the evolution of snake fangs is that the fangs did not evolve initially for the use of venom, but for swallowing. It is believed that snake fangs evolved from posterior maxillary teeth. The elongation of these teeth increased the effectiveness of swallowing for snakes. The teeth are able to swing through a longer retraction arc than other maxillary teeth allowing the snake to swallow more at one time. It is believed that after this that two separate evolutionary lineages took place. The first, the use of the elongated maxillary teeth for the use of swallowing (Xenodon and Heterodon snakes). The second, the elongated maxillary teeth for the use of venom usage (Viperidae family).

Kardong, K. (1979), 'Protovipers and the evolution of snake fangs', Evolution, Vol. 33, No. 1, Pgs. 433-443.