What has at least 25 pairs of legs and can turn on a dime? That's a question researchers have been asking themselves ever since they uncovered a strange set of footprints in the Burgess Shale, a 500-million-year-old fossil field in the western Canadian Rockies. The first analysis of the comma-shaped and elliptical tracks, reported online today in the Proceedings of the Royal Society B, indicates that they belonged to a marine arthropod called Tegopelte (artist's impression above), a relation of an extinct group of hard-shelled critters known as trilobites. The size of a loaf of bread, Tegopelte was the biggest bottom-dweller known from the Burgess Shale. The tracks show that the creature was also speedy and nimble, adding to evidence that it was either a predator or a scavenger—and therefore a possible rival in importance to free-swimming predators such as the segmented arthropod Anomalocaris, which were known to have thrived in ancient seas.
See more ScienceShots.