Newly discovered footprints in Kenya are the first evidence that two different species of ancient human relatives walked the same ground at the same time 1.5 million years ago.
The researchers responsible for the find say the tracks belong to Homo erectus and Paranthropus boisei and were made within hours or days of each other, opening up new mysteries about what happened when their paths crossed.
According to a study about the discovery, published in the journal Science, the footprints were found in dried mud near a lake in northern Kenya and were buried in sediment at a known fossil site.
After analyzing the shape of the prints and the pattern of the strokes, the scientists found that the two sets were different from each other. The best explanation, they found, is that the tracks were made by two different species.
The study contributes to a growing understanding among anthropologists and paleontologists that ancient human relatives likely interacted and coexisted. And, more broadly, it raises questions about what relationships these species had.