Discovering a new species of animal is always exciting, even if that animal has been extinct for millions of years. That is what happened when Professor Sarah Gabbott from the University of Leicester School of Geography, Geology, and the Environment went digging in the Soom Shale location just north of Cape Town, South Africa.

While digging through rocks, she found a very well-preserved arthropod that has since been dubbed, “Sue” and identified to have lived 444 million years ago. Fossils are often very unusual, but this one is particularly odd in that it was preserved inside out. Figuring out exactly how and why this happened is part of the challenge that Gabbott loves about her job.

She talked about her find to IFLScience, saying:

“When I first discovered Sue in the rock layers in South Africa I knew instantly we had something very special and unusual. It took three days to carefully dig her out of the rock and we encased her in plaster of paris (like you do for a broken limb) and she was then flown back to England by British Airways who kindly gave her a first-class seat for free! She weighed 70 kilograms [11 stone].”

It isn’t often that a fossil gets to fly first class!

Getting it back to her lab is just the beginning of the hard work she had to put in to learn as much from the fossil as possible. She went on to say:

“Then the hard work started trying to work out what she was and was not. Honestly, she is so unusual that it was a real head-scratcher – none of her preserved anatomy looked like any other fossil. Then I realized there were muscles preserved and then finally the penny dropped that she was an inside-out fossil. The tough carapace that usually would be fossilized was all but missing, and yet all her insides were exquisitely well preserved.”

This animal lived during a time when the world was going through a large scale glaciation event, which was one of the five major mass extinction events in global history, this one killing around 85% of all living species at the time.

The area where this specimen was found, it is theorized, was a basin that was able to avoid the worst of the freeze, allowing life to survive (though it would have been difficult) through this period. Gabbott explains:

“We know from analyzing the chemistry of the shales that she was found in that conditions were very harsh at the bottom of the ocean at the time. There was almost no oxygen, and, in fact, there was hydrogen sulfide in the spaces between the grains of sediment. This is what gives ‘bad eggs’ their fetid smell. I think it is these unusual conditions that led to her inside-out preservation but the exact details I have yet to work out. The main mineral that replaced all her insides before they rotted away is calcium phosphate – the same mineral that our bones and teeth are made from.”

This is another great example of being able to learn a lot about the history of the Earth with limited information gathered from fossils. Gabbott published a study on her find in the journal Paleontology.

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