When work crews expanding the Pan American Highway through Northern Chile's Atacama Desert uncovered fossils of about a dozen different kinds of ancient marine mammals, researchers were only given a week to study the site.

So scientists from the Smithsonian jumped the first flight out, met up with their Chilean counterparts, and 3D scanned the entire area in order to preserve the context in which the bones were discovered.

The answers to what happened at the site are often found in the little details, like where the bones were found in relation to each other and how they were oriented. In this case, the skeletons' orientation and condition indicated that the animals died at sea, prior to burial on a tidal flat.

Researchers were amazed to find four distinct layers of bones. The site, named Cerro Ballena, Spanish for "whale hill," was the first definitive example of repeated mass strandings of marine mammals in the fossil record.

Although all the fossils have been moved to museums in the Chilean cities of Caldera and Santiago, the Smithsonian has archived the digital data, including the 3D scans from the site, at cerroballena.si.edu. Anyone can download or interact with 3D models of the fossil whale skeletons, scan Google Earth maps of the excavation quarries, look at a vast collection of high-resolution field photos and videos or take 360-degree tours of the site.

It wasn't surprising to find aquatic fossils in the desert per se, as much of what is now dry land was once under prehistoric waters, but what was puzzling was why so many animals died at this particular site? And at four distinct times?

"It happened 9 million years ago over a period of 15,000 years," Smithsonian spokesman John Gibbons said. "And it didn't kill these animals over a period of weeks or months, this was days."

Researchers assumed a red tide killed the animals, but those are generally created when the algae fish use for food mixes with poisonous human pollution.

"The big mystery is 9 million years ago there was no human pollution to cause a red tide, so what happened?" Gibbons said.

The answer: heavy rains periodically washed unusually high concentrations of iron present in the nearby mountains out to sea.

The fish ate the contaminated algae, the whales ate the poisonous fish and the currents pushed their dead or dying bodies to that area. Over time, each layer of carnage was covered up with sand.

"There are a few compelling modern examples that provide excellent analogs for the patterns we observed at Cerro Ballena – in particular, one case from the late 1980s when more than a dozen humpback whales washed ashore near Cape Cod, with no signs of trauma, but sickened by mackerel loaded with toxins from red tides," said Nicholas Pyenson, paleontologist at the Smithsonian's National Museum of Natural History.

Researchers documented the remains of 10 kinds of marine vertebrates from the site. In addition to the skeletons of the more than 40 large baleen whales, the team documented the remains of a species of sperm whale and a walrus-like whale, both of which are now extinct. They also found skeletons of billfishes, seals and aquatic sloths.

Experts suspect the entire area is a giant prehistoric aquatic graveyard and intend to return in the near future for a much more inclusive study.