Group of Construction Workers Hit Something Hard While Digging, What They Found is a Once in a Lifetime Discovery

In 2010, while doing roadwork on the Pan-American Highway near the northwestern coast of Chile, the construction crew got a surprise when it stumbled upon a massive collection of fossils including the skeletons of at least 30 large baleen whales.

An international group of paleontologists has since unearthed at least 30 large baleen whale skeletons from four distinct layers at the site, dating back six to nine million years – the first definitive examples of ancient mass strandings of whales, according to a new study. The work also fingers a possible culprit.

“I never thought I’d have to work with 40 [whale skeletons] at once,” says Nick Pyenson, a vertebrate paleontologist and curator of Fossil Marine Mammals at the Smithsonian’s National Museum of Natural History who led the excavation. “It was overwhelming.”

The area where the fossils were found has long been known locally as Cerro Ballena (“Whale Hill” in Spanish) due to other remains found three years ago including the remains of nine other kinds of marine vertebrates such ad seals, sperm whales, dolphins, and one species previously only recovered in Peru: a walrus whale that Pyenson describes as having a “bizarre Admiral Ackbar-looking face.”

The skeletons weren’t scattered throughout the 8-meter-thick deposit of sediment. Rather, the fossils were concentrated in four distinct levels. That pattern and other clues helped the paleontologists figure out what happened millions of years ago.

Once Pyenson and his team got over the enormity of their task, they began to wonder why the ancient animals had been buried in droves in essentially the same spot repeatedly over time.

Hints came from studying tiny details in fossil scans taken by two members of the Smithsonian’s 3D digitization labwhom Pyenson brought in for a week to image the fossils in order to retain information, such as how they were arranged, that would inevitably be lost as the skeletons were removed and shipped off to Chilean museums.

Pyenson’s team learned that most of the whales were preserved with their bellies facing up, suggesting they had diêd at sea rather than on land. All skeletons were also remarkably free of bite marks made by scavengers, indicating that the creatures didn’t stay long in the ocean after dying – rather, they probably washed up on land soon after perishing.

So what killed these whales? The recurring cause that makes the most sense is mass stranding due to toxins produced by harmful algal blooms, the researchers contend. Whales could have ingested the poisons when they ate fish that had, in turn, eaten the harmful algae and concentrated the toxins.

Some of the other creatures may have simply breathed in poisons that had been wafted into the air by roiling surf. Small iron-coated spheres found in some parts of the sediments near the fossils may be remains of one stage of the microorganisms involved in the algal bloom, but results aren’t conclusive.