Phylogeny and evolution of unique skull morphologies in dietary specialist African shovel-snouted snakes (Lamprophiidae: Prosymna)

Abstract

Prosymna is a specialized African snake genus lacking close relatives. The evolutionary relationships and history within Prosymna are poorly understood. Here we assembled a multi-gene data set including representatives for 11 of 16 species to investigate the phylogenetic relationships of this group. Our analyses support the monophyly of Prosymna and are congruent with species groups previously recognized on the basis of external morphology. Divergences among extant Prosymna began in the mid-Cenozoic, with the earliest divergence splitting northern from southern lineages. High-resolution computed tomography scans confirm that a specialized skull morphology is found across the genus and was probably present in the common ancestor of Prosymna. This specialization is exemplified by dentition featuring reduced anterior but greatly enlarged, blade-like posterior maxillary teeth and an unusually high degree of fusion of cranial bones. One species, P. visseri, has a hammer-like maxilla unlike that of any other known snake. Evidence for oophagy in Prosymna and the possible roles of morphological specializations in egg-slitting or egg-crushing feeding mechanisms are discussed.