Fossil footprints dating back 1.43 million years are providing new insights into hominin body size, walking style and social behavior while raising fresh questions about whether Paranthropus boisei or Homo erectus made them.
One of 1.43-million-year-old footprints found at the GaJi10 site in the Koobi Fora Formation in northern Kenya; a 15-cm (6-inch) ruler is shown for scale. Image credit: Kay Behrensmeyer.
“The sizes of the footprints indicate human-like body sizes — up to 1.8 m (5.9 feet) tall and around 75 kg,” said Dr. Kevin Hatala, a researcher at Chatham University and the Max Planck Institute for Evolutionary Anthropology.
Dr. Hatala and his colleagues analyzed 21 hominin footprints discovered at the GaJi10 site in Kenya’s Koobi Fora Formation, part of the Turkana Basin. The findings offer a rare glimpse into how ancient hominins moved across the landscape during the Early Pleistocene.
The GaJi10 site was first identified in 1978. Additional fieldwork in 2016 and 2023 substantially expanded the footprint surface, revealing many more tracks than had previously been documented.
Together, the footprints represent at least eight individuals who crossed a shallow lakeshore. Their tracks preserve evidence of body size, foot anatomy, walking mechanics and possible group behavior.
“One trackway is oriented to the east while all other tracks and trackways are oriented toward the west,” the researchers noted.
“It is possible that the east-bound individual is also sampled in the west-bound tracks, but evidence to make that determination is lacking.”
The fossil footprints preserve details of the internal structure and mechanics of the ancient feet. These features can be compared with tracks previously associated with two hominin species known to have lived in the region: Homo erectus and Paranthropus boisei.
Paranthropus boisei. Image credit: © Roman Yevseyev.
The foot mechanics recorded in the new tracks most closely resemble those previously attributed to Paranthropus boisei. The footprints show relatively flatter arches and more mobile big toes than modern human footprints—features also identified in much older tracks from Laetoli, Tanzania, which are attributed to Australopithecus afarensis.
However, the apparent body size of the GaJi10 trackmakers complicates their identification. For most of the individuals, estimates of height and body mass based on the footprints are larger than nearly all known skeletal estimates for Paranthropus boisei. Some estimates are closer to the expected size of Homo erectus.
The results point to two possible explanations. Paranthropus boisei may have reached larger body sizes and displayed greater variation than the fossil skeletons currently indicate. Alternatively, the footprints may have been made by Homo erectus individuals whose foot anatomy and walking mechanics varied more widely than previously documented.
Although the species responsible remains unresolved, the researchers suggest that several of the trackmakers were likely large adult males traveling in the same direction at approximately the same time.
If correct, the interpretation provides rare direct evidence of hominin social behavior in the fossil record. Social interactions are typically reconstructed indirectly from skeletal remains, stone tools and other archaeological evidence rather than from footprints themselves.
Homo erectus. Image credit: Yale University.
“The fact that eight, mostly adult male, Paranthropus boisei individuals seemingly traveled together as a group, without females or children, hints at a complex social structure in this species,” said Dr. Neil Roach, a researcher at Harvard University.
“They may have lived in large groups, where males competed for mates, but also tolerated each other at times for safety in a dangerous environment.”
Dr. Purity Kiura, a researcher at the National Museums of Kenya, said the fossil footprints near Lake Turkana highlight the region’s importance for understanding human evolution.
“The discovery of these fossil footprints along the margins of Lake Turkana reinforces the region’s global importance in understanding human evolution, preserving remarkable evidence of how our ancient relatives lived 1.4 million years ago,” Dr. Kiura said.
“It further strengthens Kenya’s position as one of the world’s leading paleoanthropological landscapes and highlights our responsibility to protect this irreplaceable heritage.”
The study was published this week in the Proceedings of the National Academy of Sciences.
_____
Kevin G. Hatala et al. 2026. Insights into hominin body size, locomotion, and behavior from Early Pleistocene trackways in northern Kenya. PNAS 123 (31): e2530996123; doi: 10.1073/pnas.2530996123
Source: www.sci.news