Impossible tiny fossil found

03 February 2017

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Fossilised Loriciferan

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A type of fossil less than a millimetre long and believed originally to be impossible to find, has been unexpectedly discovered by researchers surveying mudstone samples from Western Canada.

The new fossil is a member of a new species of an animal group known as "Loricifera". It dates from a period called the "Cambrian Explosion" half a billion years ago when early life began to diversify. Leicester University's Tom Harvey and Cambridge University's Nicholas Butterfield, who discovered it, have named the new species Eolorica deadwoodensis, which means ‘ancient corset-animal from rocks of the Deadwood Formation’ as a nod to its origins.

It was whilst surveying "micro-fossils" found in samples of sedimentary rock taken from the cores of hollow drills that Dr Harvey found specks of "mysterious fragments" which aroused his suspicion.

"[They] looked like the back ends of loriciferans, but I told myself it was impossible. Finally, however, I found an exceptionally well-preserved specimen with a fossilised head still in place, proving its identity."

During such surveys, the rock sample is dissolved in a bath of strong, hydrofluoric acid that dissolves most of the minerals leaving behind organic carbon. In a specialised process combining this acid-bath with gentle seiving, tiny fossils can be extracted for observation under a microscope.

Loricifera are tiny pineapple-shaped creatures that live between grains of sand. A bulbous body contains the animal's digestive system, while the head has multiple protruding parts. But because these animals lack bones or any kind of hard shell, scientists had thought it was virtually impossible for them to fossilise. Despite this, the bodies of the loriciferans are encased in a softer material called "cuticle", which in extremely rare cases can also fossilise. "They’re very easy to overlook; even the modern ones weren’t noticed until the 1980s because they’re so tiny," says Harvey.

Even with their miniscule size, loricifera play an important part in the natural world, recycling nutrients in marine ecosystems.

"Unknown to many people, there is a hidden world of tiny animals inhabiting the spaces between sand grains on beaches and under the sea."

In addition to aiding the understanding of modern day ecosystems, a fossilised, adult loriciferan can inform us of the environmental conditions that existed 500 million years ago. Much like today, the evolutionary pressures of catching prey or evading predators were widespread in the animal kingdom.

This biological competition is what drove many species to become larger in size, but the evidence suggests that loriciferans instead bucked this trend and evolved to become smaller, shrinking to spend their entire life cycle in the sediment, although why they did so currently remains a mystery.

At present, it’s difficult to tell whether the fossil is a once-in-a-lifetime find or the beginning of a new research strategy. There is hope that since loricifera shells were found in different sediment samples, such fossils may be more widespread than first thought.  “Now we know how to look for it, we can apply this technique to other rocks around the world,” says Harvey.

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