But until now, scientists had no idea what killed them.
Apparently, poisoning from common ocean algae might have been the culprit, say researchers who published their findings in a paper titled "Repeated mass strandings of Miocene marine mammals from Atacama Region of Chile point to sudden death at sea" in the journal Proceedings of the Royal Society B.
Discovered in 2010, Cerro Ballena, or Whale Hill, consists of at least 40 dead whales along with many other extinct species.
The algae that produced a deadly neurotoxin was either ingested or inhaled by these marine animals, Nicholas Pyenson of the Smithsonian’s National Museum of Natural History, lead author of the study told the Monitor.
For example – the whales could have died after ingesting animals that fed on the algae. This is probably how the toxins found their way into many of these creatures that could have died within a few hours or days, she adds.
The most important clue came from the orientation of the bones. Many of the whale skeletons were found belly-up, suggested that they died in the sea. Also, the bodies were washed ashore quickly, before ocean scavengers could feed on them.
"These big hunks of meat stranded on a tidal flat, yet there were no terrestrial predators like a bear, nothing really larger than a dog, that could dismember the carcasses and carry the bones away,” Pyenson said in a press release.
The researchers also noted the presence of orange, iron-rich, mat-like structures on the skeletons.
“In the modern world, dissolved iron promotes harmful algae blooms and the Andes are very iron-rich. So we argue that the mountains east of the site are the ultimate source of what’s powering these ancient blooms," said Pyenson in the press release.
More evidence comes from the wide fossil assemblages, including several whale species (mostly baleen whales), marlins, two different species of seal, an extinct walrus-like whale, and an aquatic sloth that is also extinct. This indicates that the calamity was not an illness or a virus that struck certain organisms. It had to be something that could affect all of them, Pyenson told the Monitor.
This study is important because it offers a clear window into the food web that was part of the marine ecosystem many years ago, says Pyenson.