More than a million years ago, in a hot savannah filled with wildlife by the future Lake Turkana in Kenya, two distinct species of early humans might have crossed paths while looking for food. This conclusion comes from the analysis of 1.5-million-year-old fossils, which reveal the earliest known example of two different sets of hominin footprints created around the same time along the lake shore. The scientists believe this finding will enhance our understanding of human evolution, particularly regarding how different species interacted with and competed against one another.
Over a million years ago, in a lively savannah near what would later become Lake Turkana in Kenya, two entirely different species of early humans may have encountered each other while foraging for food.
Researchers have studied fossils dating back 1.5 million years, which indicate the first example of two types of hominin footprints from the same time period left on ancient lake shores. This remarkable discovery sheds light on human evolution and the dynamics of cooperation and competition among species.
The term “hominin” refers to a subgroup of hominids, encompassing all species within the human lineage that emerged after diverging from the ancestors of great apes, which is thought to have occurred roughly 6 to 7 million years ago.
Published today in Science, this discovery provides solid evidence that various hominin species coexisted both in time and in the same environment, as they navigated risks from predators and sought food in the ancient African landscape. The footprints belonged to the species Homo erectus and Paranthropus boisei, which were two of the predominant human species during the Pleistocene Epoch, according to the researchers.
“The close timing and shared habitat indicated by their tracks suggest that these two species were present near the lake, utilizing the same area,” stated Craig Feibel, a co-author of the study and a professor at Rutgers University in the Department of Earth and Planetary Sciences and Anthropology.
Feibel has been conducting research in northern Kenya, a site rich in fossils, since 1981. Using his expertise in geological studies and dating techniques, he confirmed the fossils are indeed 1.5 million years old and analyzed the conditions in which the footprints formed, concluding that the track makers were there within a few hours of each other, at the same soft sediment location.
Whether they directly interacted or simply walked the shore at around the same time remains unclear, Feibel noted.
While skeletal remains have long been the primary means of understanding human evolution, new findings based on fossilized footprints unveil intriguing details about ancient human movement and behavior. According to Kevin Hatala, the lead author of the study and a biology professor at Chatham University in Pittsburgh, Pa., these footprints present opportunities to understand how early humans navigated their environments and interacted with one another and other species—insights not easily gleaned from bones or tools.
“Fossil footprints are fascinating because they offer vivid glimpses of our ancient relatives in action,” said Hatala, who has researched hominin footprints since 2012. “These data help us observe how individuals lived millions of years ago and their potential interactions, which skeletal remains don’t reveal.”
Hatala, who specializes in the anatomy of feet, noted that the different species left distinct patterns of footprints due to variations in anatomy and movement. He and his colleagues employed innovative techniques for a three-dimensional analysis to differentiate the sets of footprints.
“In biological anthropology, we strive to find new methods to interpret behaviors from fossil evidence, and this study is a prime example,” said Rebecca Ferrell, a program director at the National Science Foundation, who supported this research segment. “The use of advanced 3D imaging technologies allows a transformative approach to studying footprints, contributing to our understanding of human evolution, as well as cooperation and competition within it.”
Feibel described the discovery as somewhat unexpected. The fossil footprints were found in 2021 by a team led by Louise Leakey, a third-generation paleontologist related to famous figures in the field.
The research team, managed by Cyprian Nyete, consists largely of skilled local Kenyans who routinely examine the area following heavy rains. They identified fossils on the surface and began excavating to locate the source. During their work, excavator Richard Loki first discovered a giant bird track, then the initial hominin footprint, prompting Leakey to organize a team for further excavation in July 2022.
Feibel pointed out that it has long been suggested that these human species existed simultaneously. Fossil records indicate that Homo erectus, a direct human ancestor, survived for another million years, while Paranthropus boisei went extinct within the subsequent few hundred thousand years for reasons currently unknown.
Both species were capable of upright walking and were agile. However, little is understood about their interactions, both in terms of culture and reproduction.
The footprints have great importance, according to Feibel, as they fall under the category of “trace fossils”—evidence of behavior that includes tracks, nests, and burrows as opposed to body fossils like bones. While body fossils can be displaced by natural forces, trace fossils remain stationary.
“This discovery conclusively shows that at least two different hominins walked on the same surface, quite possibly within hours of each other,” Feibel stated. “While it’s not surprising that they lived at the same time, this is the first evidence confirming it. That’s a significant finding.”
