Crustaceans are some of the most widely spread arthropods on the planet. Having evolved over 500 million years ago, they have diversified and spread, filling nearly all the different ecological niches on Earth. On land woodlice can be found under almost every stone or within leaf litter. In the seas hordes of crabs and lobsters click and crawl across the ocean bed, resplendent in coats of coloured armour.
Such creatures are certainly not rare, but the most diverse crustaceans on Earth, as well as in the fossil record, are tiny bivalve-like creatures called ostracods. Even the largest are no more than 3 centimetres in length, but size is no guarantee of evolutionary success. Fossils of ostracods are littered throughout the fossil record. Most are simply preserved as single shells, but occasionally something more interesting is unearthed.
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Recently two specimens of ostracod were recovered from 425 million year old rocks in Herefordshire on the English-Welsh border by a team of palaeontologists led by Dr David Siveter from the University of Leicester. Normally, analyzing fossils is not much of a challenge. The larger the creature is, the easier it is to identify features.
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The two ostracods on the other hand presented something of a challenge. They were small and very delicate and as a result, removing the rock would have destroyed the fossil. CT scans were also out of the question as the density of the fossils and the surrounding rock were so similar that no useful images could be obtained. Instead they had to resort to older and more primitive methods.
Physical tomography involves grinding down the fossil in 20 micrometer increments and photographing the surface of the fossil at each stage with a highly sensitive camera. After imaging 500 slices, the fossil was destroyed, but the team had enough data to build a computer model from these.
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The computer models of the 425 million year old ostracod
Pauline avibella from fourdifferent angles |
It was evidently a new species which was named Pauline avibella or beautiful bird on account of the shell's similarity to a pair of wings. What is interesting is the preservation of the soft-tissue. 'Ostracods are the most abundant fossil arthropods, occurring ubiquitously as bivalved shells in rocks of the last 490 million years, and are common in most water environments today,' said Siveter.
Soft part preservation is rare, but vital to our understanding of evolution. Yet this group of arthropods has a hidden, new identity.....'A case of a wolf in sheep's clothing.'
