A new species of primitive arthropod dating back 444 million years has been discovered in the Soom Shale, a site north of Cape Town in South Africa. The baffling specimen is so bizarre that its exact evolutionary relationships remain frustratingly elusive, says discoverer Professor Sarah Gabbott from the University of Leicester School of Geography, Geology and the Environment. Why? Because, bafflingly, it was preserved inside out.
Palaeontology is a lot like detective work. You are presented with limited information, you have to piece together clues to work out the time of death, and the identity of the remains. Sometimes that means lugging a fossil home before you can even begin trying to work it out, but nobody ever said you can’t travel in style.
None of her preserved anatomy looked like any other fossil
Professor Sarah Gabbott
“When I first discovered Sue in the rock layers in South Africa I knew instantly we had something very special and unusual,” Gabbott told IFLScience. “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].”
“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 realised 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.”
Professor Sarah Gabbott near the site where the fossil was discovered.
Image credit: University of Leicester
Around 440 million years ago, the planet was experiencing a glaciation event that would wipe out 85 percent of the species alive on Earth, marking one of the Big Five mass extinctions (though we may be entering a sixth). The theory is that the specific marine basin Sue was preserved in was a kind of refuge that escaped the worst of the freeze, creating a small pocket where life could survive, but the conditions were far from ideal.
I think it is these unusual conditions that led to her inside-out preservation
Professor Sarah Gabbott
“We know from analysing the chemistry of the shales that she was found in that conditions were very harsh at the bottom of the ocean at the time,” said Gabbott. “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.”
Exquisitely well preserved as she may be, it made things trickier when it came to finding Sue’s place on the tree of life, as there was so much detail to interpret. Following what Gabbott describes as an “ultramarathon of a research effort” that represents 25 years of searching, the fossil has finally been described in a new paper. It’s named Keurbos susanae after Gabbott’s mom, who told her, “If you are going to name this fossil after me, you’d better get on and do it before I am in the ground and fossilized myself.”
“I tell my mum, in jest, that I named the fossil Sue after her because she is a well-preserved specimen,” said Gabbott in a statement. “But, in truth, I named her Sue because my mum always said I should follow a career that makes me happy – whatever that may be. For me that is digging rocks, finding fossils and then trying to figure out how they lived what they tell us about ancient life and evolution on Earth.”
A remarkable fossil discovery, and a really rather lovely story.
The study is published in the journal Palaeontology.
Source Link: Meet Sue The Fossil, An “Inside-out, Legless, Headless Wonder” That Dates Back 444 Million Years
