Archaeologists working on the eastern coast of England have found a series of footprints that were made by human ancestors sometime between one million and 780,000 years ago. Pressed into estuary mudflats now hard with age, these prints are the oldest ones known outside of Africa, where humanity arose.

Scientists discovered the prints in early May 2013, at a seaside site in Happisburgh. High seas had eroded the beach sand to reveal the mudflats underneath. The team had to act quickly to record the tracks before they, too, eroded. The researchers used a technique called multi-image photogrammetry and laser scanning to capture the prints in three dimensions.

In a paper published this past February in PLOS ONE, Nick Ashton of the British Museum and his colleagues reported that analysis of the footprints—which show impressions of the arch, ball, heel and toes of several individuals—suggests they were left by a party of five as they walked south along a large river. Based on the apparent foot lengths, they ranged in height from 0.93 to 1.73 meters, evidence that the group was composed of both adults and youngsters. The researchers estimated the body mass of the adults at 48 to 53 kilograms.

Exactly which species of early human left the trails is unknown because no human remains have turned up at the site. Yet judging from the antiquity of the prints, a likely candidate is Homo antecessor, a species known from the site of Atapuerca in Spain that had body dimensions similar to those reconstructed for the largest Happisburgh footprint makers.

Happisburgh is the oldest known site of human occupation in northern Europe. Previous excavations there have turned up dozens of flint tools that these ancient people may have used to butcher animals or process their skins. Where had the track makers come from, and where were they going? Perhaps continuing erosion of the coastline will reveal more clues to the lives they lived.