Researchers were left scratching their heads in 2011 when they came upon a trove of whale fossils between 6 million and 9 million years old, of all places in Chile's Atacama Desert. It featured dozens of specimens, accounting for "at least 10 different kinds of marine animals, recurring in four different layers," researcher Nick Pyenson tells the Smithsonian. Among them were "walrus whales—dolphins that evolved a walrus-like face. And then there were these bizarre aquatic sloths," he says, per the BBC. "It begged for an explanation." Now, that explanation has arrived, via a crafty solution to a major setback: The nearby Pan-American Highway was being widened at the time of the find, requiring the quick removal of the fossils. That meant experts couldn't study the spot's geology for hints.
Fortunately, researchers were able, in effect, to take the site with them. Lasers allowed them to scan the area and the fossils and re-create them digitally, in 3D. What they found: Four fossil deposits occurred over a 16,000-year period. The whales were upside-down, suggesting they'd arrived dead, Pyenson says, and neither a tidal wave nor a virus looked likely. "I realized there's only one good explanation for it: harmful algal blooms," he says. They can be fueled by iron deposits, which are plentiful on the local coast. And the algae can be toxic to herbivores—as well as the carnivores who eat those herbivores. Even breathing the blooms can be fatal, the BBC notes. After the die-offs, water pushed the animals into an estuary, then onto sand flats, ultimately resulting in the graveyard. Click for more, including a 3D model of a fossil.