Towards the origin of South African tortoises: a new Chersina species from the Early Pliocene fossil site of Langebaanweg

Abstract

South Africa is currently home to a highly diverse tortoise assemblage whose evolutionary history has been investigated mostly as a result of molecular studies. The fossil record is of little help because the remains of extant taxa are relatively recent, and only three extinct species, of uncertain relationships, have been described so far. An Early Pliocene extinct species of the currently monotypic genus Chersina, still inhabiting South Africa, was reported at the fossil-rich site of Langebaanweg more than 50 years ago but never formally described. Here we erect and describe the extinct species Chersina langebaanwegi sp. nov. on the basis of abundant material that provides information on its morphological variation. The referral of the new species to the genus Chersina is supported by phylogenetic analysis which includes the Malagasy ploughshare tortoise, sharing the presence of a single gular shield covering a very long gular protrusion with Chersina spp. and a domed shell with C. langebaanwegi sp. nov. The material from Langebaanweg represents the oldest fossil evidence of this genus. It significantly post-dates the branching of Chersina from its sister taxon Chersobius, but pre-dates the presumed split of the extant lineages of Chersina angulata as estimated on molecular basis.