It is believed that the significant discovery of whales in Chile’s Atacama Desert may have been caused by mass strandings due to the ingestion of toxic algae.

Scientists believe they have solved the mystery of a graveyard of whales found next to the Pan-American Highway in Chile that is believed to date back five million years. This discovery is considered one of the most remarkable fossil finds in recent years. According to a report published today in the Royal Society Journal B, the whales may have died due to consuming toxic algae, causing four mass strandings. The animal remains were carried into an estuary and covered by sand, which preserved the fossils over time.

The Atacama Desert in northern Chile is known for its ability to preserve whale fossils. The site was discovered during an expansion project of the Pan-American Highway in 2010. Bones could be seen sticking out of rock faces, which led to the nickname “Cerro Ballena,” or “whale hill.”

In 2011, American and Chilean paleontologists were given a rare opportunity to properly examine fossil beds when the Highway was being widened. The team from the Smithsonian’s National Museum of Natural History and Chilean scientists had only two weeks to conduct their investigations before the construction of the new road resumed. During this time, the team created 3D models of the skeletal remains on site and recorded as much detail as possible. Some bones were also taken from the site for further laboratory study.

The team discovered the skeletons of more than 40 large baleen whales, as well as an extinct walrus-like whale and the remains of billfishes, seals, and aquatic sloths. Nicholas Pyenson, a paleontologist at the Smithsonian, expressed amazement at the density of species found in the 240m road-cut, stating that it included all the superstars of the fossil marine-mammal world in South America in the Late Miocene.

The team also noted how the carcasses were arranged. The skeletons, which were nearly all complete, were preserved in four separate levels, pointing to a repeated and similar underlying cause of death. But the different fossil levels suggested it was not one event but four separate episodes spread over a period of several thousand years.

From their research, the scientists concluded toxins generated by harmful algal blooms are likely to have poisoned the animals. If the algae were inhaled or large quantities of contaminated prey consumed, death would have been rapid.

“All the creatures we found – whether whales, seals or billfishes – fed high up in marine food webs and that would have made them very susceptible to harmful algal blooms,” Dr Pyenson said.

The bodies would then have been funnelled into a restricted area by the coastline at Cerro Ballena in the late Miocene period (five to 11-million-years-ago). Once stranded on the tidal flat, the dead or dying animals would have been protected from marine scavengers.

However, the team could not say for certain that harmful algal blooms were responsible for the mass strandings, as there were no distinct algal cell fragments present in the sediments. They did find multiple grains encrusted in iron oxides that could suggest past algal activity.

Dr Pyenson added: “They’re found in algal-like mats all around the site. We can’t say whether those were the killer algae, but they do not falsify the argument for harmful algal blooms being the cause in the way that the sedimentology falsifies tsunami being a potential cause.”