Algae killed the group of ancient whales and other aquatic species that once rested in a bone yard in an area of Chile now covered in desert, National Geographic reported. The fossils of sea creatures six to nine million years old were discovered and excavated in 2011 during construction to expand the Pan-American Highway.

Though workers removed specimens carefully, paleontologists knew that once they were gone and the road was built, evidence explaining their mass death would also be gone. Thus, digital experts from the Smithsonian Institution created a computerized model of the area before construction began so scientists could ascertain the exact cause of death. They did and published their findings in the journal, Proceedings of the Royal Society B, on Wednesday.

According to the study's lead author, Nick Pyenson of the Smithsonian, algae is the only explanation. Viruses are usually species-specific and a tsunami couldn't have only killed larger animals and spared smaller ones (of which none were found). Besides whales (some now extinct), scientists found well-preserved, belly-up skeletons of dolphins, seals (including one new species), an aquatic sloth (extinct), and the walrus-whale, or "a bizarre prehistoric dolphin with a tusked walrus-esque face," according to Nat Geo.

Algae, which killed whales trapped in Cape Cod in 1987, can inject lethal levels of toxins into the water when they overpopulate from an unusually high influx of nutrients. That's what Pyenson believes happened in Chile.

"Every explanation must work across all the taxa, and must also satisfy what you see about the bones and their arrangement," Pyenson told Nat Geo. "And it has to explain the pattern four times."

Further evidence supporting Pyenson's theory were discolorations on the animals' bones, remnants of the poisoning. His team also discovered bone imprints the exact size of dinoflagellates, a creature that contributes to algae blooms.

The mass of bones found in 2011 leads Pyenson to wonder how many more were lost during the original construction of the Pan-American Highway.

"What did they obliterate when they built the first two lanes of highway?" he asked. "They must have dug up bone after bone."

At least there is one silver-lining.

"I wouldn't wish a whale skeleton on anyone," Pyenson said. "You're going to have to dig a lot."