This article is more than 6 years old

This article is more than 6 years old

A mass graveyard of fossilised whales unearthed in Chile was created by four separate strandings over a period of 10,000 years, scientists believe.

The skeletons of dozens of baleen whales were found in ancient sandstones beside the Pan-American Highway in the Atacama region of north Chile, where they are thought to have lain undetected for between 6m and 9m years.

Whale fossil graveyard in Chile. Photograph: Adam Metallo/Smithsonian Institution

In an article published in the Royal Society journal, researchers explain the animals ate toxic algae before being washed into an estuary and eventually on to flat sands at the site dubbed Cerro Ballena ("whale hill").

Nicholas Pyenson, a palaeontologist at the Smithsonian's National Museum of Natural History, told the BBC: "We found extinct creatures such as walrus whales – dolphins that evolved a walrus-like face. And then there were these bizarre aquatic sloths.

Chilean and Smithsonian paleontologists study several fossil whale skeletons at Cerro Ballena. Photograph: James Parham/California State University, Fullerton

"To me, it's amazing that in 240 metres of road-cut, we managed to sample all the superstars of the fossil marine-mammal world in South America in the late miocene. Just an incredibly dense accumulation of species."

Cerro Ballena was famed locally for its hidden ancient skeletons – but the latest discovery was made by chance during construction work on the busy Pan-American Highway that runs alongside the area, which is now seen as one of the richest fossil sites in the world.

From left, Adam Metallo and Vince Rossi use high-res laser arm scanners to document one of the most complete fossil whales from the Cerro Ballena site. Photograph: Smithsonian Institution

Many of the fossils were found in perfect condition, with the skeletons of two adults whales laid on top of the skeleton of a juvenile whale.

The remains of an extinct species of sperm whale, a walrus-like toothed whale, an aquatic sloth and two seals were also uncovered at the site, but scientists believe there may be hundreds more ancient creatures waiting to be discovered.

Chilean and Smithsonian paleontologists study fossil whale skeletons at Cerro Ballena. Photo: Adam Metallo/Smithsonian Institution

Sol Square, a palaeontologist who worked on the discovery, described the find as "a discovery of global importance".

"There has never been a find of this size or this diversity anywhere in the world, which is one of the very special parts of the Atacama region."