Frog Mystery Surfaces at Iron Age Settlement

Excavations carried out ahead of highway work in England have revealed a mass grave full of … long-dead frogs. Experts are at a loss to explain the mass of 8,000 bones from roughly 350 frogs and toads, found buried in a long ditch beside an excavated roundhouse at Bar Hill near Cambridge, where a settlement existed more than 2,000 years ago. "To have so many bones coming from one ditch is extraordinary," Vicki Ewens, senior archaeozoologist at the Museum of London Archaeology, tells the Observer. It's "a puzzling and unexpected find, which we are still trying to fully understand," she adds, per the Cambridge Independent.

Adding to the prehistoric frog mystery is the fact that the bones show no sign of bites, cuts, or burns indicating that the amphibians were eaten, per the Observer. It's possible they were boiled before becoming dinner. But they might instead have become stuck in the ditch or died while hibernating during an especially harsh winter long ago. Another possibility is that the frogs and toads were killed by disease like the highly infectious ranavirus, which wiped out a number of common frogs during the 1980s. Or it could be that the deaths were "caused by a number of different factors, possibly interacting over a long period of time," Ewens tells the Independent. "We just aren't sure yet what these were."

Though frogs and toads were highly regarded for an association with fertility, likely due to their connection to water, in ancient Egypt, Mesopotamia, and among the Aztecs, there is no evidence of such significance in European Iron Age societies so as to explain the grave, Smithsonian reports. However they died, the frogs may have been originally drawn to the area by beetles and aphids feasting on the settlement's crops—scientists also found evidence of grain processing, per the BBC. (More frogs stories.)