More than 8,000 amphibian bones dating back to the Iron Age and weighing almost 700kg have been uncovered in Cambridgeshire.

Researchers from the Museum of London Archaeology (MOLA) found that the bones recovered by zooarchaeologists between 2016 and 2018 were those of at least 350 individual frogs and toads.

The settlement where the bones were uncovered was in use from the Iron Age to the Roman period, circa 400 BC – 70 AD.

Most of the frog bones were discovered in a 14-metre long ditch to the side of a roundhouse, which was in use during the middle and late Iron Age.

Dr Vicki Ewens, senior archaeozoologist at MOLA, said: “This is a puzzling and unexpected find, which we are still trying to fully understand.

“This accumulation of frog remains may have been caused by a number of different factors, possibly interacting over a long period of time.”

The bones were identified following an archaeology programme along the A14 Cambridge to Huntingdon improvement scheme by National Highways.

Most of the findings at the site in Bar Hill were linked to domestic animals, such as cattle.

But after analysis by zooarchaeologists, they were mystified as to how a large volume of frog and toad bones were gathered in one area of the site.

Some theories include the frogs being consumed as no traces on the bones could be seen, frogs acting as predators and the possibility of a ‘prehistoric frog tragedy’.

MOLA zooarchaeologists believe the frogs may have been unable to climb out of the 14m ditch, and that an unusual death toll may have been caused by winter hardship.

Cambs Times: Location of the roundhouse in Bar Hill where the frog bones were found.Location of the roundhouse in Bar Hill where the frog bones were found. (Image: MOLA Headland Infrastructure)

MOLA also think “the unusual mortality might have been caused by a disease.

“In the 1980s, UK frogs were heavily affected by a ranavirus; a similar disease might have had devastating effects on the amphibian population at Bar Hill.”

The two-year archaeology programme along the A14 comprised over 40 separate excavations covering around 578 acres.

Cambs Times: Over 8,000 frog and toad bones were unearthed at this site in Bar Hill, Cambridgeshire.Over 8,000 frog and toad bones were unearthed at this site in Bar Hill, Cambridgeshire. (Image: MOLA Headland Infrastructure)

Archaeologists continue to review the evidence from the A14 Cambridge to Huntingdon improvement scheme, with more data due to become available.

But for this frog mystery, questions still remain.