Preliminary phylogenetics and biogeographic history of the Pliocene seal, Homiphoca capensis from Langebaanweg, South Africa

Abstract

A phylogenetic analysis of the Langebaanweg seals was undertaken to better understand their relationships. The fossil phocid seals from Langebaanweg nest within the Lobodontini and form a clade that includes Ommatophoca rossii (Ross seal). The Langebaanweg seals' relationships are unresolved in both analyses. Two analyses were performed producing differing results. The prior weights analysis produced a clade that included the Ross seal (Ommatophoca rossii) + the Langebaanweg seals + the remaining Antarctic lobodontines. The implied weights analysis (k=3) produced a clade including the South American seals (Hadrokirus and Piscophoca) + the Ross seal (Ommatophoca rossii) + the Langebaanweg seals, which is part of the polytomy that includes the clade including the leopard seal (Hydrurga leptonyx) and the crabeater seal (Lobodon carcinophaga) and Acrophoca longirostis. In both analyses the monophyletic group LBW-F + LBW-D + LBW-A is retained while the monophyletic group LBW-C + LBW-B from the first analysis is replaced by the polytomy LBW-B + LBW-C + LBW-E in the second. The collapse of the monophyletic group LBW-C + LBW-B is due to its poor support (20), most likely as a result of LBW-C being incomplete caudally. Island hopping is proposed as a means for phocid seal migration to South Africa. The presence of islands along South Africa's west coast and phocid seal adaptation to a life independent of land and the use of ice as haul out sites lend support to this theory. During the Pleistocene, the decrease in local sea levels resulted in the loss of islands which may have resulted in the extinction of these seals over time.

Keywords:

• Pliocene
• Homiphoca
• phocid seal
• phylogenetics
• biogeography

ACKNOWLEDGEMENTS

I would like to thank Dr Nestor Abdala, Dr Ken Angielczyk and Emil Krupandan for their help with the phylogenetics; Dr Margaret Avery for editorial comments; and Dr Irina Koretsky for comments on an early version. I would also like to thank the two reviewers for their helpful comments.

Additional information

Funding

The TNT program is made available with the sponsorship of the Willi Hennig Society.