Researchers have identified 21 ancient hominin footprints at a site beside Lake Turkana in Kenya. The tracks, made 1.43 million years ago, do not match the expected features of either Homo erectus or Paranthropus boisei, the two species known to have lived in the area at that time.
The footprints were left by a group of eight individuals crossing a shallow mudflat at the edge of the lake, where water was between 2 and 10 centimetres deep. The site, called GaJi10, was first noted in 1978, and the tracks were preserved in mud alongside those of hippos, bovids, birds and equids.
Analysis shows the prints share some traits with those attributed to Paranthropus boisei, such as flatter arches and an angled big toe, yet they are much larger than expected for that species. If made by P. boisei, the individuals would have stood over 180 centimetres tall, exceeding previous estimates of the species’ maximum height.
The shape of the prints does not align with known Homo erectus tracks from the region either. Kevin Hatala of Chatham University said the findings either extend the known size range for P. boisei or reveal greater variation in H. erectus foot morphology than previously observed in modern humans.
Hatala noted that a third, unknown species is unlikely given the existing fossil record from the area and period. The group that made the tracks was probably composed of males travelling together.