No, it’s not a sand sculpture competition. The skeleton shapes are fossils, some of at least 40 dead whales washed ashore en masse between 6 and 9 million years ago on a beach that is now slightly inland from northern Chile’s coastline. They provide the earliest known example in the fossil record of mass strandings of marine mammals.
The area has the greatest density of extinct marine mammals in the world, says Nicholas Pyenson of the Smithsonian Institution’s National Museum of Natural History in Washington DC, who led the research. Unfortunately, much of the site now sits under the northbound lane of the Pan-American Highway.
Discovered in 2010 during excavations for the road, which links Alaska and Argentina, the fossil haul includes over 40 large baleen whales, an extinct species of sperm whale and an extinct walrus-like whale. Also found at the Cerro Ballena site – Spanish for “whale hill” – were skeletons of billfishes, seals and aquatic sloths.
Researchers recorded the skeletons in situ using 3D photography (pictured above) before moving them to Chilean museums.
Pyenson and his colleagues think that the whales died at sea after consuming food contaminated with toxins from algal blooms and their bodies floated onto what was then a beach. So-called “red tides”, caused by algal blooms, are also to blame for some modern mass whale strandings, says Pyenson.
There were no large land scavengers in South America at the time, so the bodies lay unmolested until sand buried them. The skeletons were found on four separate levels, suggesting this story was repeated at least four times.
Much of the site is now paved over, but the researchers are confident that the area still conceals hundreds more fossils. The University of Chile in Santiago aims to open a research station near the Cerro Ballena site to work with what’s left.
Repeated mass strandings of Miocene marine mammals from Atacama Region of Chile point to sudden death at sea
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.