LONDON.- For the first time ever, all of the known fossils collected by Charles Darwin during his voyage on the Beagle were brought together under the Natural History Museum roof.

The final fossils to be digitised were two halves of a single Megatherium skull collected in 1832 by the young naturalist in Punta Alta, Argentina. They were brought to the Museum to be 3D scanned as part of the digitisation programme.

The Megatherium was a giant ground sloth native to South America. Growing to the size of an elephant, they were some of the largest land animals roaming the landscape when they lived some 10,000 years ago.

During his voyage, Darwin actually collected a number of different ground sloth fossils which would turn out to be from four different species. Of these, three were new to science.

Dr Pip Brewer, Curator of Fossil Mammals at the Museum, says, 'Megatherium was actually one of the few fossil mammals from South America that were known before Darwin went on his trip.'

On the trail of Darwin's fossil mammals
The Darwin fossil mammal collection has been pieced together through a little bit of detective work by Dr Pip Brewer and Prof Adrian Lister, as over the past 150 years it had got somewhat complicated.

'We've been trying to document every specimen, understand where it came from and even work out whether it was definitely one of Darwin's in the first place,' says Pip. 'Bizarrely nobody had really done that in any detail before.'

Considering the pivotal role that these fossils likely played in laying the foundations for Darwin's theory of evolution, this is surprising.

The majority of these fossils have ended up in the Museum's collection, with just one remaining at the Royal College of Surgeons (RCS), where Darwin was initially sending the specimens during his voyage (the Museum didn't exist at that time).

Over the years, specimens have been lost, forgotten and added to the collection, meaning Pip and Adrian have had to go through all the documents tracing each and every one.

'Looking at the specimens Darwin recounted in his journals and the notes he made at the time, we've been tracing the fossils right the way through to the present, trying to find a definite connection about what he was talking about and what we have in front of us,' says Pip.

It was this search that led the researchers to Darwin's former home, Down House.
The missing piece

While staff at Down House were not aware of Darwin's mammal fossils in their collection, they did have some intriguing specimens which were brought out for Pip and Adrian during a visit.

'The minute we walked into the room at Down House we knew what the specimen was,' says Pip, recounting her trip. 'It had been figured by Richard Owen and is the other half of a fossil we'd seen before at the RCS.'

It turned out that when Owen received the Megatherium fossil skull from Darwin, he cut it in two to study how the teeth of the extinct animal were formed.

'This helped Owen understand how the teeth grew, what the animals ate and how they would have lived in their environment,' explains Pip.

This not only confirmed that despite its colossal size Megatherium's closest relatives were modern-day sloths, but it was the first time that anyone had moved beyond the purely descriptive and started exploring these fossil creatures as animals that were once alive.

Darwin's Megatherium skull also proved to be a vital piece in an entirely different puzzle.

At the time that Darwin's fossils started trickling back from his voyage, scientists were in the middle of casting the Megatherium skeleton that is still on display in the Museum on Fossil Way. But there was a problem.

'They were missing the back of the skull,' says Pip. 'But when Darwin sent the back of the Megatherium skull to Owen, it meant that they could finally complete the full skeleton.'

Scanning for the future
By 3D scanning all of Darwin's mammal fossils, researchers at the Museum want to both permanently preserve them and increase their accessibility not only other scientists but anyone who might have a passing interest in these specimens.

'Having a digital surrogate not only reduces handling, but also gives access for people around the world, be them researchers wanting to study them or the public who are just interested and want to see them,' explains Pip.

Already the project is showing its worth. The previously scanned Toxodon skull, which once belonged to a now extinct rhino-like animal native to South America, has been viewed thousands of times and the model has been downloaded and printed around the world.

It has been used in engagement activities in the Museum and elsewhere including by researchers at in the Western Science Centre in California, the United States, and by Adrian during talks to English Heritage at Down House and at the Chilean Congress of Palaeontology.