For millions of years the earth's earliest creatures were obliged to remain in the marine realm. Eventually, however, some animals evolved features that allowed them to establish a toehold on land. Evidence of these ancient trailblazers is vanishingly rare, but a new discovery indicates that they took their first steps ashore far earlier than previously thought. According to a report published in the May issue of the journal Geology, researchers have discovered in an inactive quarry near Kingston, Ontario, footprints preserved in sandstone that date to about 530 million years ago--pushing the date of landfall back some 40 million years.

The track makers appear to have been fairly large, amphibious arthropods--creatures today represented by crabs, spiders and insects, among others. Specifically, study authors Robert B. MacNaughton of the Geological Survey of Canada and his colleagues posit that the prints belong to a group of centipede-like beasts known as the Euthycarcinoidea. Judging from the nature of the tracks and of the sediments themselves, the team surmises that the animals were commuting in groups from sea to shore, perhaps to forage or to breed.

"We suggest that this occurrence represents an early phase of arthropod terrestrialization, during which individuals left the sea, probably for a limited time," the authors write. "That they found a new world of developing ecological niches may explain why the arthropods continued these early experiments, becoming the predominant land dwellers they are today."