Cast of a trail of hominid footprints fossilized in volcanic ash. The trail was found by Mary Leakey's expedition at Laetoli, Tanzania in 1976. It dates from 3.6 million years ago and shows that hominids (probably Australopithecus afarensis) had acquired the upright, bipedal, free-striding gait of modern man by this time. The footprints show a well developed arch to the foot and no divergence of the big toe. The prints are from two adults, and possibly a third set belonging to a child who walked in the footsteps of one of the adults.