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The Weird Wonders
Inside locked cabinets at the Smithsonian Institution nestle snapshots in stone as vivid as any photograph. There, engraved on slices of ink-black shale, are the myriad inhabitants of a vanished world, from plump Aysheaia prancing on caterpillar-like legs to crafty Ottoia, lurking in a burrow and extending its predatory proboscis. Excavated in the early 1900s from a geological formation in the Canadian Rockies known as the Burgess Shale, these relics of the earliest animals to appear on earth are now revered as priceless treasures. Yet for half a century after their discovery, the Burgess Shale fossils attracted little scientific attention as researchers concentrated on creatures that were larger and easier to understand — like the dinosaurs that roamed the earth nearly 300 million years later.
Then, starting in the late 1960s, three paleontologists — Harry Whittington of the University of Cambridge in England and his two students, Derek Briggs and Simon Conway Morris — embarked on a methodical re-examination of the Burgess Shale fossils. Under bright lights and powerful microscopes, they coaxed fine-grain anatomical detail from the shale's stony secrets: the remains of small but substantial animals that were overtaken by a roaring underwater mudslide 515 million years ago and swept into water so deep and oxygen-free that the bacteria that should have decayed their tissues couldn't survive. Preserved were not just the hard-shelled creatures familiar to Darwin and his contemporaries but also the fossilized remains of soft-bodied beasts like Aysheaia and Ottoia. More astonishing still were remnants of delicate interior structures, like Ottoia's gut with its last, partly digested meal.
Soon, inspired reconstructions of the Cambrian bestiary began to create a stir at paleontological gatherings. Startled laughter greeted the unveiling of oddball Opabinia, with its five eyes and fire-hose-like proboscis. Credibility was strained by Hallucigenia, when Conway Morris depicted it as dancing along on needle-sharp legs, and also by Wiwaxia, a whimsical armored slug with two rows of upright scales. And then there was Anomalocaris, a fearsome predator that caught its victims with spiny appendages and crushed them between jaws that closed like the shutter of a camera. "Weird wonders," Harvard University paleontologist Stephen Jay Gould called them in his 1989 book, Wonderful Life, which celebrated the strangeness of the Burgess Shale animals.
But even as Wonderful Life was being published, the discovery of new Cambrian-era fossil beds in Sirius Passet, Greenland, and Yunnan, China, was stripping some of the weirdness from the wonders. Hallucigenia's impossibly pointed legs, for example, were unmasked as the upside-down spines of a prehistoric velvet worm. In similar fashion, Wiwaxia, some scientists think, is probably allied with living bristle worms. And the anomalocaridids — whose variety is rapidly expanding with further research — appear to be cousins, if not sisters, of the amazingly diverse arthropods.