Credit: Adam Metallo/Smithsonian Inst.

The unearthing of more than 40 marine mammal fossils (pictured) at a site in Atacama, Chile, has revealed that they probably died en masse in four events due to toxic algae.

Nicholas Pyenson of the Smithsonian Institution in Washington DC and his colleagues found that the fossils, including baleen and other whales, seals and an aquatic sloth, were arranged in four distinct layers, which are between 9 million and 6.5 million years old. The only modern event known to trigger such recurring and rapid die-offs of multiple species is extreme growth of toxic algae. The animals could have died after eating contaminated prey or have been directly affected by the algae's toxin. Other ocean areas that once created such blooms could harbour substantial fossil vertebrate remains, the authors say.

Proc. R. Soc. B 281, 20133316 (2014)