Scientists know this because they have examined 1.5-million-year-old fossils they unearthed and have concluded they represent the first example of two sets of hominin footprints made about the same time on an ancient lake shore.
A fossil first: Scientists find 1.5-million-year-old footprints of two different species of human ancestors at same spot
A neat find. I heard a passing reference to it today on the radio and saw it in the news now.
When hominins walked in each others’ tracks
John Hawks’ take.