Laetoli in brief
Laetoli lies on the dry Serengeti plateau in northern Tanzania, about 45 kilometres south of Olduvai Gorge, in the Ngorongoro Conservation Area. The name comes from the Maasai word for the red lily that grows there. The area’s ancient layers, the Laetolil Beds, are between about 3.8 and 3.6 million years old, and they hold fossils of many kinds of animals, with early human relatives among them.
It is known above all for a trail of footprints, the oldest clear evidence that human relatives walked upright.
The first expeditions
The German collector Ludwig Kohl-Larsen found part of an early human upper jaw in the area in 1939, and Louis Leakey visited the area in 1935. Mary Leakey returned in 1974 and led teams there for several years. Her team found a lower jaw with teeth in 1974, catalogued LH 4 (Laetoli Hominid 4). It was later chosen as the name-bearing specimen of Australopithecus afarensis, which is why a species named for Ethiopia’s Afar region has its type specimen in Tanzania.
The footprints
The footprints were found in stages. In 1976, members of Mary Leakey’s team, including the geologist Andrew Hill, noticed animal prints in a layer of hardened volcanic ash while throwing lumps of elephant dung at each other, and soon found tracks of many animals: elephants, giraffes, rhinoceroses, hares and many birds. In 1978 Paul Abell found the first of the human-like prints, and the team excavated a trail about 27 metres long.
The trail has about 70 prints, left by at least two, and perhaps three, individuals walking side by side, in volcanic ash (long thought to come from the nearby volcano Sadiman, though that is now doubted) that was then dampened by rain. The ash then hardened and was covered by more ash. Radiometric dating of the layer gives an age of about 3.66 million years.
The prints show a heel strike, a rounded arch and a big toe in line with the other toes, as in a modern foot. That was strong support for the idea that the makers walked on two legs in a human way, a claim that was challenged by some scholars. Later studies of the stride and the depth of the prints suggested a slightly bent-hip, bent-knee gait or a more upright one, and researchers still debate the details. The makers are usually thought to be A. afarensis, the only known hominin species at Laetoli at that time.
In 2015 a team led by Fidelis Masao found more tracks at a nearby spot, from at least two more individuals of the same age, one of them larger than any of those in the first trail. That fits the evidence from Hadar that males of this species were much bigger than females.
Protecting the trail
After its excavation in the late 1970s, the trail was covered again, to protect it from erosion and from the roots of acacia trees that were growing in the ash. It was reburied in 1979. A conservation project run by the Getty Conservation Institute and Tanzanian authorities examined and reopened it in the 1990s and re-covered it. Today the original prints stay buried, and casts and replicas are shown instead.
Why it matters
Laetoli showed that walking upright was established more than 3.6 million years ago, well before the species of Homo appeared, and from the prints alone it gives a picture of a small group of individuals going across an ash-covered landscape, with animals around them, soon after a volcanic eruption. Both the footprints and the jaw are in the same layers, so the site holds, in one place, a record of the species’ walking and its anatomy.
Visiting
The Laetoli site is within the Ngorongoro Conservation Area, a World Heritage Site, and access to the trail is limited. Visitors can see displays, casts and information at the Olduvai Gorge museum and at the National Museum in Dar es Salaam. See also Olduvai Gorge.
Sources
- Leakey, M. D. and Hay, R. L. (1979). Pliocene footprints in the Laetolil Beds at Laetoli, northern Tanzania. Nature 278: 317 to 323.
- Masao, F. T. and others (2016). New footprints from Laetoli (Tanzania) provide evidence for marked body size variation in early hominins. eLife 5: e19568.
- Agnew, N. and Demas, M. (1998). Preserving the Laetoli footprints. Scientific American 279(3): 44 to 55.
- Smithsonian National Museum of Natural History, Human Origins Program. Laetoli footprints.