Spirals in Time: The Secret Life and Curious Afterlife of Seashells Read Online Free PDF Page A

particular fossil at the Burgess Shale, a part of which had already been found elsewhere. Twelveyears previously, Canadian palaeontologist G.F. Matthew had found a single, ribbed spine while fossil hunting in the Wiwaxy Peaks in the Rockies. He called it Wiwaxia . Walcott was the first to find fossilised remains of the complete animal. He decided it was a type of bristly worm known as a polychaete, a member of the annelid phylum. But it didn’t have much in common with any living polychaete worms. Wiwaxia looked more like a slug fitted out with a suit of overlapping body armour, and with elongated knife blades sticking up in two rows along its back.
    Walcott found hundreds of Wiwaxia, including two-millimetre-long spineless specimens and larger ones, up to five centimetres (two inches) in length. And yet, peculiar as they were, Wiwaxia and the other fossils found in the Burgess Shale didn’t raise much more scientific interest for the next 50 years. Walcott is perhaps best remembered now as the man who didn’t quite realise what astonishing things he had found.
    It was only in the 1960s that palaeontologist Harry Whittington from Yale University decided to take another look. Whittington had already revolutionised the world of trilobite studies when he uncovered silica specimens, fossils made essentially of glass, that revealed dainty details of their mysterious lives. His interest in trilobites led him to the Rockies, where he reopened excavations of the Burgess Shale deposits and began a monumental task that would continue for the rest of his life.
    Whittington took up a professorship at the University of Cambridge where, along with his research students Derek Briggs and Simon Conway Morris, he reassessed the Burgess Shale fossils. Together they opened a new window into the origins of animal life. It was through their work that the concept of the ‘Cambrian explosion’ took hold, where a plethora of complex animals appeared in a sudden flurry (although more recently the pace and duration of these changes have been questioned). Evolution seemed to be tinkering with the possibilities for life.
    Among the piles of new discoveries and reinterpretations, it was Conway Morris who re-examined Wiwaxia and decided that it wasn’t a polychaete worm after all. Inside Wiwaxia ’s mouth he found two rows of backward-pointing teeth that he thought were rather familiar. They looked to him like the rasping radula (a feature of many modern molluscs, which we will return to shortly).
    While he thought the rest of Wiwaxia ’s body was too strange to win it a formal place within the mollusc phylum, Conway Morris interpreted the fossil as being a common ancestor of the group. Was this odd, spiny slug the precursor to mollusc life? Little did Conway Morris know at the time, but debates over the true identity of Wiwaxia had only just begun.
    Since then, Wiwaxia has suffered from an identity crisis as people argued over whether it was a worm, or a mollusc, or something else. Nick Butterfield, also at Cambridge, waded in on the discussions early on and pushed Wiwaxia back worm-wards. He pointed out that Wiwaxia ’s sclerites (the ribbed scales of its body armour) were built more like a worm’s bristles; what’s more, its mouthparts could have been split and arranged in two parts on the sides of its head, a distinctly worm-like trait.
    Wiwaxia isn’t the only problematic proto-mollusc of the Burgess Shale fossils. In the original excavations Walcott found a single fossil of Odontogriphus , a flattened, oval creature that grew up to 12.5 centimetres (close to five inches) long, with a hardened covering across its back. It had a small, circular mouth on its underside that seemed to be adorned with radula-like chompers just like Wiwaxia .
    Conway Morris looked at Odontogriphus again in the 1970s and concluded it was a common ancestor to the worms, molluscs and brachiopods. Then in 2006, after nearly 200 more specimens were found, Jean-Bernard