Thousands of years ago, a swath of land along what is now the western coast of England served as a superhighway for humans and animals alike. Today, the ebb and flow of each passing tide reveals more of the ancient footprints that these long-gone travelers stamped into the once mud-caked route.
Reminders of their travels can be seen along a nearly 2-mile-long (3 kilometers) stretch of coastline near Formby, England. The footprint beds show how, as glaciers melted and sea levels rose after the last ice age ended around 11,700 years ago, humans and animals were forced inland, thus forming a hub of human and animal activity seen in the commingled footprints.
In a new study published in the October issue of Nature Ecology and Evolution (opens in new tab), researchers found that the trackways, some of which are more than 8,000 years old, date from the Mesolithic period, or Middle Stone Age (15,000 B.C. to 50 B.C.) to medieval times (from A.D. 476 to A.D. 1450). Researchers recovered seeds from alder, birch and spruce trees scattered within the layers of the route and radiocarbon-dated them to pinpoint the age of the tracks.
In total, there are a dozen "well-preserved" footprint beds, some of which are stacked, creating roughly 36 exposed layers, or "outcrops." These patchworks of prints contain foot impressions from not only humans but a variety of animals, including aurochs (an extinct species of ox), red deer, wild boars, wolves, lynx and cranes.
"Only some of the outcrops are visible at any one time," Alison Burns, the study's lead author and an archaeologist at The University of Manchester in England, told Live Science. "The farther down you [dig], the older the outcroppings are."
Related: Ice-age children frolicked in 'giant sloth puddles' 11,000 years ago, footprints reveal
The mishmash of tracks was originally discovered in the late 1970s by a geologist who thought they were "cattle footprints.” In the 1990s, a retired teacher saw the trackways and began dating them, "realizing that they were of some antiquity," Burns said. "Before then, people didn't think [the prints] were particularly interesting or old."
Since then, the footprints have continued to reveal themselves "due to erosion of the coastline as the sea eats away at the covering sand dunes that helped to preserve the footprints," Burns said.
"The footprints are preserved under the sand, and as the coastline is being eroded, the water is eating away at the cover that helped preserve them," Burns said. "When the tracks were made, they were filled with sand and then a layer of mud. That's how you get these stacks [of footprints]. Once you have four or five beds on top of each other, the top layer is vulnerable [to erosion], but the ones beneath it are quite well preserved."
Of the dozens of prints discovered at the site, one in particular stood out, not only because it's the oldest track, imprinted approximately 8,500 years ago, but also due to the story it told researchers, Burns said.
"It was a human track that proceeded forward four or five paces and then the person stopped," Burns said. "They were barefoot, and the footprints were fantastic; the mud has oozed up between each toe, so you get all the features of the footprint. Immediately adjacent to them were prints from a crane. The person could very well have been looking for birds to hunt during a scouting expedition. And beside the crane, there is a clear set of adult red deer tracks nearby. Within 2 square meters [22 square feet], we get this amazing snapshot of the past."
However, the discovery of footprint impressions "isn't unique to the area," she said. One nearby archaeological site contains 900,000-year-old human prints (opens in new tab) exposed during a 2013 storm in Norfolk, located about 250 miles (400 km) to the southeast of Formby. But what makes the Formby site special is that it reveals how humans and animals lived together thousands of years ago.
"Many footprint studies typically focus on the human prints and not the animal prints," Burns said. "I was really interested in seeing how the animals and humans shared this very populated environment."