Millions of years ago, a mysterious event may have turned a section of the Pacific Ocean near Chile, into a veritable killing field for thousands of whales.

Paleontologists working in an area within Chile's Atacama Desert have discovered the fossilized remains of a large number of whales and other marine animals. Around six to nine million years ago, these aquatic animals died in en masse and it appears that they died because they were stranded, an event that seemed to have occurred quite often.

"At least ten different kinds of marine animals, recurring in four different layers," said Nick Pyenson, a researcher from the Smithsonian Institute. "It begged for an explanation."

The scientists onsite found numerous fossilized remains, included several extinct species of whales such as a type of sperm whale and another species of whale that looked similar to a walrus. Moreover, the scientists also found around thirty baleen whales and numerous other animals such as bony fish, seals and aquatic sloths.

While most paleontologists would be giddy with excitement at such a large find, they faced a pressing problem. A highway that ran through the whale graveyard was scheduled to be widened soon giving the scientists a mere two months to get their affairs in order. 

While they could probably just dig up everything and take them to a lab for further analysis, scientists needed enough data about the intact site to study how these animals died. Working against the clock, the researchers used lasers to create a 3D map of the entire site. The 3D renderings can then be used to study the fossils exactly as they were originally entombed within the sediments of the Atacama Desert.

While the mass whale graveyard was found in the middle of the desert, the animals actually perished in a different location, the scientists said. They probably died somewhere off the coast of South America. The bodies were then washed ashore ending up in a tidal mudflat that was slowly covered with sediments until the remains were buried underground. Millions of years later, the remains became fossilized over time and subduction gradually lifted the sediments containing the fossils by as much as 130 feet.

"The baleen whales were mostly belly-up, and whales are generally only belly-up if they arrive at someplace dead," Pyenson said. "This is a graveyard, it's not a murder site-the murder happened elsewhere."

Having solved the mystery of an aquatic animal graveyard in the middle of the desert, scientists then turned their attention to another enigma. What killed all of these marine animals?

"I realized there's only one good explanation for it: harmful algal blooms," said Pyenson.

These algal blooms can occur suddenly and cause the deaths of thousands of marine animals. In fact, mass die-offs due to algal blooms still happen in modern times. Large concentrations of certain types of algae can produce a fatal amount of toxins that can kill off large numbers of herbivorous marine animals. Since the toxins can accumulate in the bodies of the herbivores, carnivores can also die from eating the affected plant eaters.

The researchers published their findings about the site in the online journal Proceedings of the Royal Society B.

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