Taxonomical review of Prosymna angolensis Boulenger, 1915 (Elapoidea, Prosymnidae) with the description of two new species

African Shovel-snout snakes (Prosymna Gray, 1849) are small, semi-fossorial snakes with a unique compressed and beak-like snout. Prosymna occur mainly in the savanna of sub-Saharan Africa. Of the 16 currently recognised species, four occur in Angola: Prosymna ambigua Bocage, 1873, P. angolensis Boulenger, 1915, P. frontalis (Peters, 1867), and P. visseri FitzSimons, 1959. The taxonomical status and evolutionary relationships of P. angolensis have never been assessed due to the lack of genetic material. This species is known to occur from western Angola southwards to Namibia, and eastwards to Zambia, Botswana and Zimbabwe. The species shows considerable variation in dorsal colouration across its range, and with the lower ventral scales count, an ‘eastern race’ was suggested. In recent years, Prosymna material from different parts of Angola has been collected, and with phylogenetic analysis and High Resolution X-ray Computed Tomography, the taxonomic status of these populations can be reviewed. Strong phylogenetic evidence was found to include the angolensis subgroup as part of the larger sundevalli group, and the existence of three phylogenetic lineages within the angolensis subgroup were identified, which each exhibit clear morphological and colouration differences. One of these lineages is assigned to the nominotypical P. angolensis and the other two described as new species, one of which corroborates the distinct eastern population previously detected. These results reinforce that a considerable part of Angolan herpetological diversity is still to be described and the need for further studies.