Hallucigenia sparsa from the Burgess Shale (Royal Ontario Museum 61513). The fossil is 15 mm long. Credit: Jean-Bernard Caron A new study of an otherworldly creature from half a billion years ago - a worm-like animal with legs, spikes and a head difficult to distinguish from its tail - has definitively identified its head for the first time, and revealed a previously unknown ring of teeth and a pair of simple eyes. The results, published today in the journal Nature, have helped scientists reconstruct what the common ancestor of everything from tiny roundworms to huge lobsters might have looked like....