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.

Cranial osteology of Hypoptophis (Aparallactinae: Atractaspididae: Caenophidia), with a discussion on the evolution of its fossorial adaptations

“…Some other aparallactines have a similar premaxilla–maxilla contact, mediated by somewhat similar modifications on the contact surfaces of both bones. The prosymnid Prosymna lineata has a similar contact between these two elements (Figure 5 of Heinicke et al, 2020 ). Among the basal fossorial alethinophidians, various forms of contact between the transverse process of the premaxilla and maxilla have also been noted (Comeaux et al, 2010 ; Frazzetta, 1999 ; Olori & Bell, 2012 ; Rieppel & Maisano, 2007 ; Rieppel & Zaher, 2002 ).…”

“…The one Hypoptophis specimen (RBINS‐VER‐REP 9711) with its parabasisphenoid and basioccipital almost completely fused may be indicative of a tendency toward fusion. A tendency toward fusion is seen in burrowing prosymnids as well (Heinicke et al, 2020 ).…”