About 1.5m years ago a big-toothed cousin of prehistoric humans walked quickly along a lakeside in Kenya, footprints marking the muddy ground. But they were not our only ancestor on the scene: treading the same ground was the early human Homo erectus.

Researchers say an analysis of fossilised footprints discovered in deposits of the Turkana Basin, northern Kenya, suggest the marks were made by two different species on the human family tree who were in the same place within hours or days of each other.