Fossil footprints preserved along the ancient shoreline of Kenya's Lake Turkana are reshaping scientists' understanding of Paranthropus boisei, an extinct human relative that lived 1.4 million years ago.
The trackway, described in a study published in late August 2026 by researchers from the Max Planck Institute and the Smithsonian Institution, contains the footprints of at least eight individuals who appear to have traveled together across an ancient lakeside landscape. The finding provides a rare snapshot of social behavior in a species known primarily from skulls and bone fragments.
Most strikingly, the footprints suggest that P. boisei was significantly larger than scientists had estimated from skeletal remains alone. The foot sizes implied by the trackway indicate individuals standing roughly 1.5 meters (about 5 feet) tall and weighing up to 50 kilograms — considerably larger than previous estimates based on fragmentary fossils.
The body sizes suggested by the footprints would make P. boisei at 1.4 million years ago essentially indistinguishable in stature from contemporary Homo erectus individuals whose tracks were found at the same site. This overlap raises provocative questions about how these two human species coexisted in the same landscape and whether they competed for resources.
The footprints also provide evidence that P. boisei was not the solitary, small-bodied forager that some scientists had envisioned. Instead, the group of eight individuals traveling together suggests social coordination and potentially cooperative behavior.
The discovery adds to a growing body of evidence that Paranthropus, long dismissed as a failed evolutionary side branch, was a more successful and adaptable genus than previously appreciated. Its disappearance from the fossil record around 1 million years ago remains one of paleoanthropology's enduring mysteries.
