Reacción a "Footprints of coexistence of different hominids described in Kenya 1.5 million years ago"

Kevin Hatala and co-workers have found a series of undoubtedly human footprints with bipedal locomotion, together with faunal tracks at the edge of a palaeolake with a chronology of about 1.5 million years. There is at least a trail of more than ten footprints and other isolated tracks.

The main novelty of this article (apart from the fact that they are hitherto unknown tracks) is that two different kinetic patterns of bipedalism can be observed among these tracks. That is, two different ways of stepping. Both are bipedal with the adducted big toe typical of bipedalism and different from the chimpanzee footprint. This leads them to consider that they may belong to two different taxa with different footfall biomechanics. They compare with other footprints from the African fossil record of similar chronology and observe that there are also two footprint patterns in different sites. But this would be the first time that both patterns have been observed at the same site.

Here comes the biggest limitation when studying footprints in archaeological sites: it is to know who made those footprints. In this case, at least two taxa of humans or hominins (H. ergaster/erectus and Paranthropus boisei) are represented in East Africa. Homo ergaster is a larger-bodied species than paranthropes, which resemble australopithecines in body size. Both population groups inhabit the region in these chronologies. The kinematic and size study of the footprints from this site of the KBS member allows them to possibly be associated with these two groups. When one looks at the fossil record of Homo erectus and Paranthropus boisei from the region in these chronologies, it is interesting to note that there are also two different morphologies in the different bones of the foot. Thus, at Koobi Fora, around a lake 1.5 million years ago, we have two types of footprints (in terms of kinetics/biomechanics of the footprint and in terms of overall size). In the same region there are at least two different hominin foot morphologies corresponding to a large-bodied species (H. erectus) and a small-bodied species (P. boisei). Most likely then, both types of footprints are made by these two types of hominins, indicating that both human groups coexist with slightly different ecological and environmental requirements. The authors propose at this point a possible low ecological competitiveness between Paranthropus boisei and Homo erectus.