Anatomical and landmark morphometric analysis of fossil phocid seal remains from Langebaanweg, West Coast of South Africa

Abstract

ABSTRACT Langebaanweg (LBW) is a Mio-Pliocene fossil site located on the west coast of South Africa, approximately 120 km north of Cape Town. The combination of terrestrial, riverine and marine fauna suggests that it was an estuary at the time of deposition. Early studies of the fossil phocid seal, Homiphoca capensis, from LBW suggested that it is morphologically intermediate between the monk and Antarctic phocid seal, with close affinities to the crabeater seal in particular. Here we re-examine the fossil phocid seal collection, using both descriptive and morphometric approaches, and reveal substantial variation in cranial and postcranial skeletons. The variation present in the postcranium suggests that two morphotypes are present in the sample. The morphometric analyses of the crania confirm that the LBW seals are similar in many respects, including overall size, to extant crabeater seals. However, the LBW seals appear to be more variable than any individual extant seal taxon, while examination of fine-scale shape variation in the sample identifies three distinct cranial morphotypes. Together the results of the postcranial and cranial analyses suggest the presence of two or possibly three seal taxa, indicating a greater diversity of pinnipeds at LBW than previously appreciated.