1.4-Million-Year-Old Footprints Reveal a Surprisingly Large, Social Human Relative

A set of fossil footprints preserved in Kenya for 1.4 million years is rewriting what scientists thought they knew about one of humanity's ancient relatives - both how big it was, and how it lived.

The tracks were uncovered in the Koobi Fora Formation near Lake Turkana and date to roughly 1.43 million years ago. They capture a single moment frozen in time: at least eight individuals of Paranthropus boisei, an extinct hominin species known for its massive jaw and teeth, walking together across wet ground moments before the surface hardened and locked their footprints in place.

The most striking finding is size. Based on the depth and spacing of the prints, researchers estimate some individuals stood up to 1.8 meters tall and weighed around 75 kilograms - dramatically larger than earlier estimates, which were based on a handful of rare fossil bones and had pegged the species as considerably smaller and more ape-like in stature.

Just as significant is what the footprints reveal about behavior. The group appears to have been made up mostly of adult males traveling together, with no clear evidence of females or juveniles in the tracks. "The fact that eight, mostly adult male, P. boisei individuals seemingly traveled together as a group, without females or children, hints at a complex social structure in this species," said Neil Roach, a researcher at Harvard University involved in the study.

Fossil bones can tell scientists a lot about anatomy, but they rarely reveal behavior - footprints are one of the few kinds of evidence that capture a moment of actual activity, rather than just physical remains. The research, published in Proceedings of the National Academy of Sciences and led by teams from Chatham University and the Max Planck Institute for Evolutionary Anthropology, adds Paranthropus boisei to a short list of ancient hominin species where fossilized "behavior" - not just bones - has actually survived to be studied.