Around 1.5 million years ago there were several different types of pre- and early humans in Africa. However, it was previously unclear whether these hominins met each other and even occurred in the same area at the same time. Now prehistoric footprints in Koobi Fora on Lake Turkana in Kenya provide proof of this. Based on the shape and sequence of the footprints, researchers have determined that these 1.5 million-year-old traces come from two different species of humans: the early human Homo erectus and the Paranthropus boisei, a robust, more primitive pre-human species. Both hominins must have walked along the same lake shore within a few hours of each other. For the first time, this clearly confirms that different human species coexisted in one habitat, as the team reports.
It has long been known from fossil finds that human evolution was not straight and linear. Instead, many different species of hominins evolved over time, some of which became our ancestors, but others of which died out without descendants. Bone finds suggest that some of these species probably lived in the “cradles of humanity” in East and Southern Africa at the same time. “However, the sites of such hominin fossils are often spread over hundreds to thousands of square kilometers and time periods of thousands to tens of thousands of years,” explain Kevin Hatala from Chatham University in Pittsburgh and his colleagues. As a result, the spatial-temporal resolution is not sufficient to be able to say whether two species actually occurred together in an area.
One continuous track and several individual prints
Footprints in the famous fossil site of Koobi Fora on Lake Turkana in Kenya now provide more information. Since the discovery of this site by the paleoanthropologist Richard Leakey in 1969, more than 10,000 fossils of various pre- and early human species as well as stone tools and animal bones have been unearthed. The hominin bones come from pre-humans such as Paranthropus boisei, who lived around 2.3 to 1.4 million years ago, as well as from early humans of the genus Homo such as Homo ergaster, Homo rudolfensis and Homo erectus. In 2007, fossilized footprints of Homo erectus were discovered nearby, demonstrating its advanced foot anatomy and ability to walk on two legs.
Now more footprints have been added: They were discovered in 2021 by a team led by Louise Leakey from Stony Brook University and uncovered in the summer of 2022. The footprints consist of a continuous track of one person as well as several individual prints that appear to be from three other people. The team reports that the prints of various animals can also be seen in the same layer, including prehistoric marabous. They date the prints to be 1.52 million years old. “Fossil footprints are exciting because they represent snapshots that provide insight into the lives of our fossil relatives,” says Hatala. “From such data we can see how individuals moved through their environment millions of years ago and interacted with each other or with other animals. This is something that bones or stone tools cannot provide us with.”
Imprints of Homo erectus and Paranthropus boisei
Closer analyzes of the human footprints revealed that the continuous track and the individual prints cannot come from representatives of the same hominin species – they are too different in both their anatomy and their movement patterns, as Hatala and his colleagues explain. The isolated footprints therefore closely resemble the footprints of modern humans. “The HT1 track, on the other hand, shows a different kinematic pattern,” write the researchers. “They are shallower and less deep and are more similar to the 3.6-million-year-old traces of Laetoli in Tanzania.” Based on the characteristics, they assign the individual prints to the early human Homo erectus. The continuous trace, however, comes from a representative of Paranthropus boisei. This pre-human species, characterized by strong jaws and a robust physique, had a smaller brain and a less balanced upright gait than Homo erectus.
Despite these differences, the footprints show that these two hominin species occurred in the same habitat at the same time around Lake Turkana around 1.52 million years ago. “They prove beyond any doubt that not just one, but two hominin representatives walked over the same surface – at most a few hours apart,” says co-author Craig Feibel from Rutgers University. “While the fact that these species occurred at the same time is not surprising, this is the first clear evidence. This is really a big deal.” The team says the tracks suggest that the shores of Lake Turkana were an important resource for both species – and that they probably had little competition for each other. The jaws and teeth of Paranthropus boisei suggest that its diet consisted primarily of grasses, grass seeds and tubers, similar to today’s baboons. Homo erectus, on the other hand, were hunters and gatherers and had a much more flexible diet that also included fruit, meat and fish.
The lake shore and the surrounding landscape could therefore have provided both hominin species with sufficient food without them being in direct competition with each other. “The results of Hatala and his team provide a fascinating insight into the behavioral ecology of co-occurring hominin species,” writes William Harcourt-Smith of the American Museum of Natural History in New York in a commentary accompanying the study. “They suggest aspects of paleobiology that are difficult to reconstruct but crucial to our understanding of these and other hominin representatives.”
Source: Kevin Hatala (Chatham University, Pittsburgh) et al., Science, doi: 10.1126/science.ado5275