Ancient bees buried in bones and fossils revealed

Ancient bees buried in bones and fossils revealed

By Stéphanie Pappas edited by Andrea Thompson

Thousands of years ago, in what is now the Dominican Republic, there was a cave filled with bones. And these bones were full of bees.

In a paleontological first, researchers have discovered that bees used the jaws of now-extinct mammals as burrows. It’s unclear exactly which species of bee exploited this grisly opportunity: only their smooth-walled nests were left behind, nestled in the tooth pockets of ancient rodents and sloths. But such behavior has never been documented before, says Lázaro Viñola López, a postdoctoral researcher at the Florida Museum of Natural History and one of the discoverers. “It was something completely unexpected,” he said.

When Viñola López and his colleagues passed through the jagged entrance to the cave, called Cueva de Mono, they were looking for fossilized lizards, which they found in excess. They also found tens of thousands of bones from extinct rodents and sloths, leading them to conclude that they had stumbled upon the battlefield of an ancient family of owls that likely nested in the cave and regurgitated the bones onto the cave floor. Although it is difficult to precisely date the fossils, the species come from the late Quaternary period, which began 125,000 years ago, and include species that went extinct more than 4,500 years ago, the researchers reported Tuesday in Royal Society Open Science.

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In the dirt filling the empty tooth sockets of the jaws of rodents and sloths, Viñola López and her colleagues noticed strange, smooth, cup-shaped structures that they eventually realized were made by bees. The hard, smooth walls are the result of a waterproof layer that solitary bees add to their brood cells, where insect larvae develop.

More than 90 percent of bee species live solo, and most dig their burrows in the ground. “Modern bees, as far as I know, don’t nest in caves, or in these sediment-filled bone cavities,” says Anthony Martin, a paleontologist at Emory University who was not involved in the study but is looking for trace fossils, or burrows and tracks left by ancient animals. He called the discovery a “two-for-one surprise.”

Viñola López and her colleagues suspect that bees were using the bones shortly after the owls burped them, and this could be because the soils of the surrounding forests were thin.

Bones filled with bee nests were found in three of the four soil layers, suggesting that bees used the cave for long periods of time. There are also unique tooth cavities filled with up to six different nests. “It’s probably several bees that come to nest together,” explains Viñola López.

The bones could have provided additional protection against predators such as parasitic wasps.

“It’s a bit like a thermos,” Martin explains. “They had this outer protective layer provided by the bone, and then they had their brooding cell, which was in the sediment, so they had double protection.”

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