Mass frog burial baffles experts at iron age site near Cambridge

Archaeologists working near the site of an iron age home near Cambridge were confused when they found a lot of frog skeletons. It's a mystery why so many bones had been preserved.

There was a settlement during the middle and late iron age at Bar Hill and they were all recovered from a 14-metre ditch. The Museum of London Archaeology (Mola) Headland Infrastructure conducted excavations as part of the national highways A14 Cambridge to Huntingdon road improvement scheme.

Archaeologists are perplexed by the number of frog bones found at Bar Hill.

Dr Vicki Ewens, Mola's senior archaeozoologist, told the Observer that they don't get a lot of Frogs. It's amazing to have so many bones coming from a single ditch.

She said that the bones are mostly from the common frog and common toad, species found in garden ponds around the country.

Two Saxon sites have single bones on them. They were only found in East Anglia in the 1990s but have recently been reintroduced.

It is difficult to find an explanation as ancient civilisations saw the frog as a symbol of fertility.

The people living at the settlement probably didn't eat the salamanders. There is evidence of amphibian consumption in Britain dating to the stone age, but the bones have no burn marks. The frog might not have left traces if it had been boiled.

Evidence of charred grain found near the site suggests that its inhabitants were processing crops that would attract pests such as beetles. The promise of food may have been a factor in the attraction of the frog to the area.

A prehistoric frog tragedy is one of the possibilities. Frogs are known to move in large numbers in the spring in order to find breeding waters and if they fall into the ditch, they could be trapped.

The death toll may have been caused by winter hardship according to one theory. It's possible that the frog fell victim to a particularly severe winter.

They may have been affected by disease like in the 1980s when the UK frog was devastated by a ranaviruses.

I don't know how deep the ditch was. The field team dug through the ground to reach the site. There were only a small amount of domestic waste found at the site.

Around 40 excavations took place over the course of two years across an area of 234 hectares and included the bones of the amphibian. Analyses are continuing even after excavations have ended.

Ewens has been studying the bones of animals. It is hoped that once all the studies are done, they will shed new light on the lives of people thousands of years ago.