As they walked across Engare Sero in northern Tanzania, a group of people left their mark in the soft surface of volcanic ash beneath their bare feet. Preserved for thousands of years in material expelled during an eruption of Oldoinyo L’engai (visible in the background), these impressions were first spotted by members of a nearby Maasai community in 2008. When a team of researchers visited the year after, they found 56 footprints exposed by natural erosion and, during the ensuing excavations, they uncovered hundreds more, bringing the total to at least 408, the largest assemblage of fossilised footprints known in Africa.

These footprints offer a snapshot of how people moved through this spot at one point in the past. A study recently published in Scientific Reports has concluded that the bulk of the tracks, dated to between 19,100 and 5,760 years ago, represent a group of 17 individuals walking together sideby- side, their paths not crossing as they head south-east. The researchers, led by Kevin Hatala of Chatham University, suggest this group was probably made up of 14 women, two men, and one juvenile male, although foot measurements are not a sure sign of age or sex. The women may have been foraging and were perhaps visited or accompanied by the males, as in some modern hunter-gatherer groups.

More tracks belong to six people heading in the opposite direction. Judging by the length of their strides, they were moving at different speeds – one woman appears to have been running – and so probably passed through separately. Tracks left by bovids, zebra, and buffalo were found nearby, and the researchers believe there are likely to be many more prints beyond the limits of the excavations.

Image: Cynthia Liutkus-Pierce