Five hundred and twenty million years ago, in the Cambrian sea, there swam and crawled a bizarre array of animals. There was Opabinia, which carried on its head a veritable cluster of eyes, not to mention a huge anterior 'sucker'. There was Anomalocaris, a swimming creature as large as a baby shark, equipped with two horrid grasping arms - jointed for all the world like those of a lobster - but with a body apparently as slick as a squid and weirdly flapped along its side. There were worms dusted with scales as dense as the down on a chick. Oddest of the oddities was Hallucigenia, a small, spindly, spiky thing, yet with tubular organs, and what may or may not have been a head. The Cambrian ocean swarmed with sea-going arthropods: jointed-legged animals, now familiar as lobsters and lice, beetles and bees, spiders and scorpions. Their original discoverer C.D. Walcott dubbed the commonest of these Cambrian beasts 'lace crabs': creatures as delicate and diaphanous as ostrich feathers, but crested in a way unlike any shrimp or woodlouse. And alongside this Marrella there were knobbly, prawn-like creatures and a dozen more puzzling or peculiar, like Sidneya inexpectans or Waptia. This was the world of the Burgess Shale, and all these creatures are known only from fossils preserved as subtle, silvery films laid out on slabs of dark shale.
LRB 1 October 1998 | PDF Download