New species revealed after 25 years of study on 'inside out' fossil -- and named after discoverer's mum

The result of 25 years of work by a University of Leicester palaeontologist and published in the journal Palaeontology, the study details a new species of multisegmented fossil and is now officially named as Keurbos susanae.

Lead author Professor Sarah Gabbott from the School of Geography, Geology and the Environment said: “‘Sue’ is an inside-out, legless, headless wonder. Remarkably her insides are a mineralised time-capsule: muscles, sinews, tendons and even guts all preserved in unimaginable detail. And yet her durable carapace, legs and head are missing – lost to decay over 440 million years ago.

“We are now sure she was a primitive marine arthropod but her precise evolutionary relationships remain frustratingly elusive.”

Today about 85% of animals on Earth are arthropods, and they include shrimps, lobsters, spiders, mites, millipedes and centipedes.

They have an excellent fossil record stretching back over 500 million years but usually their fossil remains are of their external features, whereas ‘Sue’ is the complete opposite because it is her insides that are fossilized.

The fossil was found in the Soom Shale, a band of silts and clays at a location 250 miles north of Cape Town in South Africa. These strata were laid down on the seafloor over 440 million years ago at a time when a devastating glaciation had wiped out about 85% of Earth’s species – one of the big five ‘mass extinctions’. It seems that the marine basin in which ‘Sue’ swam was somehow protected from the worst of the freezing conditions and a fascinating community of animals, including ‘Sue’, took refuge there.

The conditions in the sediments where Sue came to rest were toxic in the extreme. There was no oxygen but worse than that there was deadly (and stinking) hydrogen sulphide dissolved in the water. The researchers suspect that a strange chemical alchemy was at work in creating the fossil and its unusual inside-out preservation.

But there is a downside, because the unique preservation of ‘Sue’ makes it difficult to compare her to other fossils of the era and so it remains a mystery how she fits into the evolutionary tree of life.

The small roadside quarry where Professor Gabbott found the fossils 25 years ago at the start of her academic career has all but disappeared and so other specimens are unlikely to be found. The fossil was incredibly difficult to interpret and Professor Gabbott held out hope of finding another specimen with its head or legs intact.

Professor Gabbott adds: “This has been an ultramarathon of a research effort. In a large part because this fossil is just so beautifully preserved there’s so much anatomy there that needs interpreting. Layer upon on layer of exquisite detail and complexity. I’d always hoped to find new specimens but it seems after 25 years of searching this fossil is vanishingly rare – so I can hang on no longer. Especially as recently my mum said to me ‘Sarah 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! 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.”