Prehistoric puzzle reveals fearsome predator
EU-funded scientists have solved a prehistoric puzzle to reveal a fearsome predator that roamed the seas half a billion years ago. The new species, Hurdia victoria, was a denizen of the deep during the Cambrian period, when life underwent a period of rapid diversification and the earliest ancestors of today's species first appeared in the fossil record. Hurdia was related to the distant ancestors of the arthropods, and its discovery sheds new light on the evolution of this massive group of animals, which accounts for over three quarters of all known species and includes insects, crustaceans, spiders and millipedes. The study, which is published in the journal Science, was partly supported by the ZOONET ('Development and evolution of animal form: training modern comparative zoologists ') Marie Curie Research Training Network under the EU's Sixth Framework Programme (FP6). Hurdia was first described as a crustacean-like animal almost 100 years ago, in 1912, by the famous fossil hunter Charles Walcott. He had discovered fragments of the ancient animal in the Canadian Rockies' Burgess Shale, a fossil bed which has taught us much about life during the Cambrian period. Meanwhile, fragments of Hurdia had also been acquired by other fossil collections, but these had been incorrectly described as separate animals and had been classified variously as jellyfish, sea cucumbers and other arthropods. In the 1980s, researchers began to realise that these apparently disparate specimens were in fact parts of the same animal. Then, the discovery of new, more complete examples of Hurdia in the 1990s added weight to the theory that the official description of Hurdia was in need of revision. The final piece of the puzzle fell into place when palaeontologists retrieved a well-preserved specimen of Hurdia from the old collections of the Smithsonian National Museum of Natural History in the US. This specimen was originally classified as an unusual example of the well-known monster predator Anomalocaris. Anomalocaris and its relations were the largest predators of the Cambrian seas, and their relatively vast size and toothy mouths have led some to dub them 'the T. rex of the Cambrian'. This latest study provides an updated description of Hurdia, which turns out to be closely related to Anomalocaris. Like Anomalocaris, Hurdia has a segmented body and its head is armed with a pair of spine-like claws and a circular jaw structure bearing many teeth. The samples of Hurdia are up to 20 cm long. Hurdia specimens have been discovered as far afield as Canada, the US, eastern Europe and possibly China. According to the researchers, this suggests that the ancient predator was what is known as a generalist species, meaning one able to adapt to a range of environmental conditions. However, Hurdia differs from Anomalocaris in one important respect; half of its body length is taken up with an immense, three-part carapace that protrudes from the front of the animal's head. The function of this unusual structure has the scientists stumped. 'This structure is unlike anything seen in other fossil or living arthropods,' commented Allison Daley of Uppsala University in Sweden. 'The use of the large carapace extending from the front of its head is a mystery. In many animals, a shell or carapace is used to protect the soft parts of the body, as you would see in a crab or lobster, but this structure in Hurdia is empty and does not cover or protect the rest of the body. We can only guess at what its function might have been.' Although the study has increased our understanding of the species, it seems that there is still some way to go before the Hurdia puzzle can be fully solved.
Countries
Canada, Sweden, United Kingdom