Repeated mass strandings of Miocene marine mammals from Atacama Region of Chile point to sudden death at sea

Artículo de publicación ISIMarine mammal mass strandings have occurred for millions of years, but their origins defy singular explanations. Beyond human causes, mass strandings have been attributed to herding behaviour, large-scale oceanographic fronts and harmful algal blooms (HABs). Because algal toxins cause organ failure in marine mammals, HABs are the most common mass stranding agent with broad geographical and widespread taxonomic impact. Toxin-mediated mortalities in marine food webs have the potential to occur over geological timescales, but direct evidence for their antiquity has been lacking. Here, we describe an unusually dense accumulation of fossil marine vertebrates from Cerro Ballena, a Late Miocene locality in Atacama Region of Chile, preserving over 40 skeletons of rorqual whales, sperm whales, seals, aquatic sloths, walrus-whales and predatory bony fish.Marine mammal skeletons are distributed in four discrete horizons at the site, representing a recurring accumulation mechanism. Taphonomic analysis points to strong spatial focusing with a rapid death mechanism at sea, before being buried on a barrier-protected supratidal flat. In modern settings, HABs are the only known natural cause for such repeated, multispecies accumulations. This proposed agent suggests that upwelling zones elsewhere in the world should preserve fossil marine vertebrate accumulations in similar modes and densities.Excavation work was conducted under CMN permit no. 5979 to M.E.S. and was financed by Sacyr Chile S.A. Funding from CONICYT, Becas Chile, Departamento de Postgrado y Postı´tulo of the Vicerrectorı´a de Asuntos Acade´micos of Universidad de Chile supported C.S.G. This work was also funded by a National Museum of Natural History (NMNH) Small Grant Award, discretionary funding from NMNH Office of the Director, the Smithsonian Institution’s Remington Kellogg Fund, two National Geographic Society Committee on Research Exploration grants (8903-11, 9019-11) to N.D.P. and by U-REDES (Domeyko II UR-C12/1, Universidad de Chile) to A. O. Vargas