Pinniped turnover in the South Pacific Ocean: new evidence from the Plio-Pleistocene of the Atacama Desert, Chile

ABSTRACT

Modern pinnipeds distributed along the coasts of continental South America consist almost entirely of otariids (sea lions and fur seals). In contrast, phocids (true seals) are present only on the southernmost extreme of Chile. This recent biogeographic pattern is consistent with the zooarchaeological record (∼8–2 ka), but it is incompatible with the pinniped fossil record during the Neogene. From the middle Miocene to the Pliocene, true seals exclusively dominated pinniped assemblages, and they were only replaced by the fur seals and sea lions sometime after the early Pliocene. Here, we describe pinniped material collected from two new localities in the Atacama Desert, northern Chile, that clarifies this marine mammal faunal turnover. Specifically, these finds provide records of the first occurrence of Otariidae (late Pleistocene) and the last occurrence of Phocidae (early Pliocene) in Chile, which in turn constrain the timing of this turnover to between the early Pliocene and late Pleistocene. The stratigraphic context of these findings provides new insights into hypotheses that explain this faunal turnover in South America, and we briefly discuss them in the context of turnover events involving other marine vertebrates throughout the Southern Hemisphere.

ACKNOWLEDGMENTS

We would like to thank J. Velez-Juarbe, R. Salas-Gismondi, M. Stucchi, J. F. Parham, and D. Rubilar-Rogers for their comments and suggestions that improved the preliminary version of the manuscript. We appreciate the useful and detailed comments from the editor J. H. Geisler, as well as those from R.W. Boessenecker and an anonymous reviewer, who substantially improved the manuscript. We also thank S. Fuentes Tamblay and S. Soto Acuña for the preparation and photography, respectively, of the specimens reported here, and R. Yury-Yáñez for the assistance in the preparation of the Bahía Inglesa Formation map. For access to comparative material, we also thank D. J. Bohaska (Paleobiology) and C. W. Potter (Vertebrate Zoology) at the Smithsonian Institution's National Museum of Natural History (NMNH) in Washington, D.C. C.S.G. was funded by CONICYT, Becas Chile, Departamento de Postgrado y Postítulo of the Vicerrectoría de Asuntos Académicos of Universidad de Chile, and the Smithsonian Institution's Remington Kellogg Fund. This work was also funded by a NMNH Small Grant Award, discretionary funding from NMNH Office of the Director, the Smithsonian Institution's Remington Kellogg Fund, and two National Geographic Society Committee on Research Exploration grants (8903-11, 9019-11) to N.D.P. Permit No. 5979 was granted by the Consejo de Monumentos Nacionales. This paper is Caldera Paleontology Project contribution no. 2.

Handling editor: Jonathan Geisler