3.6 million years ago, a group of Australopithecus afarensis went out for a stroll. 40 years ago, a team lead by famed paleoanthropologist Mary Leakey found the footprints of these hominins at a site in Tanzania called Laetoli. And now today, for the first time since Leakey’s original discovery, scientists describe new footprints from the same site that reveal more about the lives of individuals from the same Australopithecus community.
This research, published today in the journal eLife by a team of scientists from Tanzania and Italy, builds upon research on the first Laetoli footprints discovered in 1976. These original tracks, from an area called Site G, represent three individuals and provided one of the first pieces of direct evidence that humans walked upright 3.6 million years ago. But while this evidence is tantalizing, it is limited.
In 2015, only 150 meters away from Site G, Fidelis Masao from the University of Dar es Salaam and colleagues made a fortuitous find. While doing a survey of the Laetoli area and assessing its viability as a site for a museum, they stumbled on something in a test pit they had not found in decades—footprints from two new early human individuals.
The footprints from these individuals at the newly named Site S were found on the same ash layer as the original Site G footprints, which now combined represent a total of five individuals. Study author Jacopo Moggi-Cecchi from University of Florence was excited about the new find because it meant more data: “Now we have a new series of quantitative data,” he says, “and step and stride length can help us figure out how large these individuals were.”
Estimates of body size from these step and stride measurements were surprising when compared to the other individuals from Site G. One of the individuals in Site S was substantially larger—about 5 feet 4 inches tall compared to the other individuals who were 4 feet 9 inches and under. This range in sizes of Au. afarensis is likely explained by sexual dimorphism, with the females outsized by males. For comparison, the male individual from Site S is nearly 20 inches taller than the most famous Au. afarensis, “Lucy.”
3.6 million years ago this was likely a dry, tropical bushland that was a popular place to hang out. Hominins were not the only living things in this area, as study author Marco Cherin from University of Perugia explains: “The entire locality is completely covered by animal footprints.” He describes over 500 footprints from small cow-like creatures (similar to dik-diks), but also gazelles, giraffes, rhinos and rabbits, conjuring up images of a busy landscape teeming with life.
Discoveries like this inspire the imagination and begin to fill in details about early human life in Laetoli. Now researchers can say with confidence this area contained five individuals of varying sizes and sexes walking on the same wet ash surface, all while surrounded by a diverse community of animals. Finds like this are not only vital for understanding how hominins moved around, but also for understanding how differences in size between sexes developed. Beyond that, Cecchi says, this find is inspiring on a uniquely human level: “We can witness where our earliest relatives took a prehistoric walk, and understand the everyday life of the species.”