When a road construction crew began to expand the two-lane Pan-American Highway in the Atacama Desert in Chile in 2010, a mass grave of marine mammals was almost lost to history. Thankfully, 3-D digitization tools and an international collaboration of researchers preserved the placement of those skeletons, allowing a unique glimpse into ancient food webs.
Now, a paper published February 25 in The Proceedings of the Royal Society B reveals how these animals likely died: a harmful algal bloom event.
“The answer comes from two major bodies of evidence: One is the orientation arrangement of the skeletons. They’re complete. In some cases they’re overlapping,” Nicholas Pyenson, lead paper author and a paleobiologist at the Smithsonian Institution, told weather.com. The other is the fact that the bones — which encompassed more than 40 skeletons and a great diversity of species, including two animals extinct today — were found in four layers rather than just one. The majority of the creatures were baleen whales, but there were also seals, aquatic sloths, even predatory fish.
Researchers used 3-D digitization tools to study a massive whale grave discovered in Atacama, Chile in 2010. Today, we understand a harmful algal bloom likely caused the mass die-off. (Smithsonian Institution)
Blooms of this type affect marine mammals even today; they ingest the toxins or eat prey that has. But we typically don’t know that’s the cause right away because it takes time to parse this out, often leaving the reasons behind mass strandings a mystery. That, Pyenson added, is one of the benefits of working at a geologic scale. “You don’t get a complete picture of life in the past, you just get these snapshots, but sometimes the snapshots are coarsened up that you can actually figure out with a large degree of certainty what happened.”
This is crucial in the case of the Atacama bones because there are still, by the scientists’ estimates, hundreds of skeletons at the site, dubbed Cerro Ballena or “Whale Hill.” They’re visible today thanks to the very highway that threatened to destroy the original mass grave. (The original bones ended up in two museums in Chile, in Santiago and in a town called Caldera.)
The researchers date the bones back some 6 to 9 million years. “It’s the richest and densest fossil whale site in the world,” Pyenson said. And thanks to some cool technology and some persistent scientists, today we have a more complete picture of what happened to these animals.
Read the full paper, “Repeated mass strandings of Miocene marine mammals from Atacama Region of Chile point to sudden death at sea,” in The Proceedings of the Royal Society B here.
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