About 1.4 million years ago, a group of ancient primates crossed a muddy shoal along the shore of what is now Lake Lorenyang in modern-day Kenya, leaving behind a trail of footprints. Over time, these prints were covered by sediment, which preserved them until today. Recent research on this trackway has revealed that, based on foot structure and gait, the footprints are more similar to those of Paranthropus boisei, yet the body size of the hominins who made them matches estimates for Homo erectus. This contradiction makes it difficult to determine the exact species responsible for the tracks.

Discovery Site and Historical Context

The GaJi10 site, located on the eastern shore of the ancient Lake Lorenyang—an ancestor of today’s Lake Turkana in northern Kenya—has been known to paleontologists since 1978. Over decades of research, numerous fossils and traces of ancient animals have been found here, including hominin footprints. Fossil evidence shows that around 1.43 million years ago, two species lived in this region: Homo erectus (upright man) and Paranthropus boisei. The latter was distinguished by massive jaws and large molars, and previous estimates suggested it was shorter and lighter than Homo erectus, with a differently shaped foot.

Footprint Analysis

Using modern technology, researchers measured the depth of each footprint, the arch volume, the angle of the big toe, stride length, and also estimated walking speed, body size, and mass. These parameters were compared with other known hominin trackways, including the 3.66-million-year-old Laetoli footprints from Tanzania, 1.5-million-year-old tracks from Kenya, and prints from modern humans.

The analysis showed that the foot structure is closer to Paranthropus boisei: these ancient hominins had a flatter arch, a different foot roll mechanism, and a big toe that pointed outward. However, the size of the footprints suggests a height of up to 180 centimeters and a body mass of 75–80 kilograms, which is significantly larger than previous estimates for Paranthropus boisei (up to 160 cm tall and about 52 kg in weight).

Possible Interpretations

If the footprints indeed belong to Paranthropus boisei, this would indicate the existence of larger individuals among them than previously thought. If, on the other hand, they were made by Homo erectus, it would suggest a much greater diversity in foot structure and gait within that species. There is also the possibility that the tracks belong to a species unknown to science, but so far, all fossils from that period in the region are linked only to the two known groups.

Social Behavior and Lifestyle

The footprints all head in the same direction and likely belong to large individuals, which may indicate that a group of adult males was moving together. This is a rare direct piece of evidence for the social behavior of ancient hominins. Usually, such conclusions are drawn from indirect signs, but here a specific moment from their lives has been preserved.

Regular visits to the lakeshore were probably connected to the search for aquatic plants, mollusks, and fish. Resource-rich areas like this could have supported the long-term coexistence of Homo erectus and Paranthropus boisei in the same region without one displacing the other.

Conclusion

The study of ancient hominin footprints on the shore of Lake Lorenyang has raised new questions about the morphology and social behavior of these species. Definitive conclusions about the identity of the trackmakers are currently impossible due to contradictions between foot structure and body size. No new remains indicating the existence of another species have been found in the region.