Saturday, March 15, 2014

[PaleoMammalogy • 2014] 'Cerro Ballena' • Repeated Mass Strandings of Miocene Marine Mammals from Atacama Region of Chile point to Sudden Death at Sea

Figure 4. High dynamic range images of orthogonal three-dimensional point clouds capturing adult and juvenile fossil rorqual skeletons from Cerro Ballena.
(a) MPC 678; (b) MPC 684; (c) over-lapping adult and juvenile specimens, clockwise MPC 666, 665 and 667; (d) MPC 685 and (e) MPC 675.
Small-scale bars 20 cm, large-scale bars 30 cm. True north indicated by arrow, and stratigraphic layer noted by bone-bearing level number.
See and the electronic supplementary information for more details and source data. DOI: 10.1098/rspb.2013.3316

Marine 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.

Keywords: taphonomy, strandings, fossil record, harmful algal blooms

Nicholas D. Pyenson, Carolina S. Gutstein, James F. Parham, Jacobus P. Le Roux, Catalina Carreño Chavarría, Holly Little, Adam Metallo, Vincent Rossi, Ana M. Valenzuela-Toro, Jorge Velez-Juarbe, Cara M. Santelli, David Rubilar Rogers, Mario A. Cozzuol and Mario E. Suárez. 2014. Repeated Mass Strandings of Miocene Marine Mammals from Atacama Region of Chile point to Sudden Death at Sea. Proc. R. Soc. B 281: 20133316.