Scientists are toadly baffled by 8,000 ancient toad and frog bones that have been found in a ditch during an excavation along a route of a new road near Cambridge, UK.

The bones were found in a 14-meter-long [6 foot] ditch during excavations between 2016- 2018. They were located by an Iron Age roundhouse that was in use in the Middle and Late Iron Ages. The depth of this ditch is unclear, as the scientists had to dig through a meter of topsoil and subsoil to reach the amphibian graveyard.  

The sheer mass of the remains in one place is an unusual and extraordinary find, and one that is a bit of a head-scratcher, as scientists do not understand how they got there.  

“In my experience, mainly working on sites from London, we don’t get that many frogs. To have so many bones coming from one ditch is extraordinary,” Vicki Ewens, Museum of London Archaeology (MOLA) senior archaeozoologist, told the Observer.

These bones seem to come mostly from the common frog and common toad species – this is a species that is found across the country.

“We’ve also had possible evidence of pool frog, which is exciting… It’s not something that we usually find archaeologically,” says Ewens. “In my research, I’ve only found two Saxon sites with single bones on each. They’re a frog that was only found in East Anglia that died out in the 1990s, possibly due to habitat loss, but has recently been reintroduced.”

Dating back to the Stone Age, there has been evidence of people chomping down on our amphibian friends. However, there are no cuts or burn marks on the bones found in the ditch, which is the typical evidence of these bones being munched on – so it is unlikely that these animals were eaten by the people in the settlement. Although if the frogs were boiled there may not be any traces of this.

At the nearby site, there was evidence of charred grain, which suggested that the inhabitants were processing crops. This crop process could have attracted other pests that are part of the amphibian’s diet, so the frogs may have been drawn to the area because of the food.

One theory for this prehistoric frog tragedy is frisky frogs could have moved into the area in the spring in search of breeding areas, and tragically fallen into the ditch and become trapped.

Alternatively, the high death could have been from winter hardship. If there was a very severe winter, the extreme cold could have killed them.

A further explanation could be from disease. There are many diseases that can affect frogs. In fact in the UK in the 1980s the froggy population was destroyed by a ranavirus. So much so that the Frog Mortality Project was set up to monitor and report the disease. Ranavirus are viruses that affect a large number of amphibians, along with some fish and/or reptiles.

“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. We just aren’t sure yet what these were!” said Ewen.

The bones were not the only ones found at the site, there were human and other animal remains, along with other artifacts.

The analysis is still being conducted on the samples and there is hope that this data will shed light on the time period. There is also hope that the amphibian death mystery will one day be solved.