Many scientists consider the ‘Cambrian explosion’ — which occurred about 530-540 million years ago — as the first major appearance of many of the world’s animal groups in the fossil record. Like adding pieces to a giant jigsaw puzzle, each discovery dating from this time period has added another piece to the evolutionary map of modern animals. Now, researchers have found a rare, 500-million-year-old ‘worm-like’ fossil called a palaeoscolecid, which is an uncommon fossil group in North America. The researchers believe this find, from an area in western Utah, can help scientists better understand how diverse the Earth’s animals were during the Cambrian explosion.