Making old bones: Joint Mitnor cave reopens with replica fossils

Experts use 3D printing to restore mound of fossilised remains in Devon quarry plundered by thieves in 2015

Future archaeologists may be seriously puzzled by Joint Mitnor, a cave in a Devon quarry. They will find a mound of fossil bones of animals, which about 120,000 years ago were unfortunate enough to fall through a sinkhole into the limestone cavern.

Among bison and hippo bones they will find the teeth of wolves, bears and elephants, and the droppings of hyenas that probably came into the cave to feast on their rotting corpses, which appear to date from the 21st century.

The cave in Buckfastleigh reopens to the public on 12 August, with all the damage and losses caused by thieves who broke in two years ago apparently miraculously undone.

Replicas of the stolen bones have been placed back in the cave through a unique collaboration between the Pengelly Trust, which manages it, the Natural History Museum (NHM) and the University of Birmingham.

The replicas were created by scanning bones in London excavated from the same cave in the 1960s, 3D-printing them in Birmingham where the complexity of the task broke two machines, and casting them in gypsum plaster in Cornwall. The casts were made in case the polymer plastic versions damaged the delicate environment where dripping limestone-rich water preserved the fossils for so long.

The NHM and the university gave their time and expertise for free. Farah Ahmed, the head of imaging at the museum, said: ‘When we heard about the Joint Mitnor cave project, we jumped at the chance to be involved.

Replicas of some of the stolen fossils in situ in Joint Mitnor cave
Replicas of some of the stolen fossils in situ in Joint Mitnor cave. Photograph: Charlie Bird

“The museum boasts some of the most advanced scanning technology in the world and by using innovative CT scanning on the museum’s own Joint Mitnor collection, we were able to create high definition 3D scans of each object.”

The Birmingham team was led by Robert Stone, professor of interactive multimedia systems and a Devonian, who said: “Our printers were set up for small industrial tasks, not for leaving them working away hour after hour on objects as complex as the elephant tooth. It broke two of them.”

His team has also created a virtual reality interpretation of the cave as it was in the temperate period between two ice ages, when lush vegetation flourished in what is now southern England.

Bison, hippos, wolves and bears roamed the region, alongside gigantic straight tusk elephants – taller than mammoths or elephants today, standing up to 4 metres tall at the shoulder – and untroubled by human beings.

Over a weekend in September 2015 thieves smashed two locks on the cave’s steel security door, broke in and stole some of the more accessible bones, damaging others in the process.

A computer-generated image of an elephant molar used to print a 3D replica
A computer-generated image of an elephant molar used to print a 3D replica. Photograph: University of Birmingham, School of Electronic, Electrical & Systems Engineering

“They weren’t just kids, it was a serious undertaking. The door was a really solid thing,” Alan Finch, a retired police officer and secretary of the William Pengelly Caves Study Trust, said.

The cave was discovered in the 1930s by two adventurous local youths who were first told by a local museum that their find was “just a bit of bison”. Scholarly excavation after the second world war uncovered a site internationally important for its exceptional fossil remains, the richest from any British cave.

Finch pointed out that although there are many such specimens in museum collections, it is very unusual for them to remain heaped in their original site and accessible to the public.

Though word was circulated through the caving and museum communities, no trace has ever surfaced of the fossils, which police and museum experts believe were stolen for sale to collectors. Pip Brewer, the NHM’s curator of fossil mammals, thinks the thieves were probably very disappointed at their haul.

“People assume that just because the fossils come from a cave and they’re very old, they must be worth a fortune, but actually hyenas are very common,” she said.

The cave will open for guided tours by members of the Pengelly Trust on Wednesdays and Thursdays until the end of August.


Maev Kennedy

The GuardianTramp

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