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john hawks weblog

paleoanthropology, genetics and evolution

Photo Credit: The cave that contains hominin footprints. Photo by Martin Lockley CC-BY

Ancient footprints emerge from the coast of South Africa

According to the Canadian Broadcasting Corporation, the hominin footprints discovered in South Africa and published last week were discovered by some dedicated avocational paleontologists: “Ancient human footprints discovered by B.C. family on vacation in South Africa”.

A B.C. family's hobby of hunting for fossils has led to the discovery of a rare set of ancient human footprints on the south coast of South Africa.
The existence of the tracks, estimated to be approximately 90,000 years old, was revealed in an article published in the open-access journal Scientific Reports, maintained by the editors of the UK publication Nature.
The lead author of the report is Charles Helm, a former family physician in Tumbler Ridge, B.C., who is originally from South Africa.

This is such a great story, a case study in how discoveries are made. Some new scientific discoveries come from exploring where nobody else has been before. But most discoveries emerge from someone looking in a well-trodden area with new eyes. They may see something that no one else has noticed before.

These footprints are actually embedded within the walls and ceiling of a cave. What is today a cave actually formed within a dune sand breccia. The erosion naturally happened along ancient natural surfaces, leaving the impressions preserved within layers that had originally filled in the footprints, stratigraphically above them.

Imagine, studying footprints on the ceiling of a cave!

Footprints in figure 4a of Helm et al 2018
Footprints illustrated in figure 4a of Helm et al. (2018)

The research paper is in Scientific Reports, which is open access: “A New Pleistocene Hominin Tracksite from the Cape South Coast, South Africa”. The paper makes it clear that this was no chance discovery. These hominin footprints were just the most interesting results of a systematic survey of coastal sites for trackway evidence.

The hominin tracks reported here were discovered as part of a ground survey by the senior author along a 275 km stretch of coastline from Witsand in the west to Robberg in the east, undertaken between 2007 and 2016 (Fig. 1). Over 100 Late Pleistocene vertebrate tracksites were identified in coastal aeolianites, and in 2016 natural cast tracks on the ceiling of a ten-metre long cave (Fig. 2) were identified as human in origin. In 2017 further hominin tracks were identified in this cave on a lower layer. The focus of this paper is to describe these tracks and to briefly place them in their sedimentary and palaeoecological context.

The larger footprints are 23 cm long, and there are shorter ones that are around 17 cm long. The paper suggests that all these footprints likely belong to modern humans. That is by no means impossible, but I note that all these footprints are within the size range that I would expect for Homo naledi as well.

It may take some time for archaeologists to change their outdated assumption that the entire African Pleistocene record documents a linear succession of modern human ancestors. With every discovery, we need to be critical about documenting context and associations.