In 1976, a trail of fossilized hominid tracks was found in Laetoli, Tanzania. These footprints were determined to be at least 3.6 million years old, and some of the earliest evidence ever found to illustrate upright, bipeDalí walking in early hominids. Thanks to a chance series of events including a volcanic eruption, a light rainfall, and a second deposit of ash, scientists today can observe firsthand the preservation of a specific moment in prehistoric time.
Laetoli was first surveyed by anthropologists in 1935, when Louis S. B. Leakey and his wife Mary D. Leakey evaluated the area. They were excavating at Olduvai Gorge 2 days to the north when Maasai tribesmen told them there were many bones at Laetoli. The team investigated when the Olduvai season ended. After making a few scattered, fragmented finds, they left. Later, during the 1938-1939 season, a German team surveyed the Laetoli area. The Leakeys returned a couple of more times, with few results. In 1974, Mary Leakey found better preserved hominid remains, resulting in a more systematic evaluation of the area. One night in 1976, team member Andrew Hill was joking around with colleagues, throwing dried elephant dung in a mock battle. As Hill ducked to avoid a hit, he noted what appeared to be animal prints preserved in the exposed volcanic tuff. Further investigation revealed a trail of hominid footprints.
The majority of the Laetoli footprint site was excavated in 1978. The exposed trail is about 80 feet long. The prints are distinctively different in size and in two parallel tracks. Despite the size disparity, the strides are the same length, indicating that the two hominids were walking together and compensating to match their strides. Scientists have disagreed as to whether the tracks represent two or three individuals. The smaller prints in the westernmost trail have sharp, clear impressions. The larger prints are blurred and more indistinct. Some argue that a third hominid was walking in the prints made by the larger individual, while others claim the larger, heavier hominid was simply sliding more in the wet ash. The footprints are almost indistinguishable from those of modern humans except for their small size. They have a deep heel impression, a distinct arch, and push off from the toes at the end of the stride. The big toe is in line with the other toes like the toes of a modern human, rather than being an opposing toe like that of a chimpanzee.
Regardless of whether the prints were made by two or three hominids, the importance of this find cannot be overstated. It is, literally, rock-solid proof that early hominids were bipeDalí long before large brains evolved and stone tools were used. The only hominid fossils found at Laetoli belong to Australopithecus afarensis, indicating that individuals of this species made the trail. Despite years of searching, no stone tools have been found in the Laetoli beds, indicating for now that hominids had not yet developed into the toolmaking stage.
Study and debate about the Laetoli footprints is ongoing, but no one can deny the uniqueness of this find. Approximately 3.6 million years ago, the Laetoli area was savanna that supported a varied animal population. At the beginning of a rainy season, Sadiman, a volcano to the east, erupted. The shower of ash was not severe enough to drive the animals away. The season brought intermittent showers, turning the ash to a fine mud that the local fauna continued to walk through. Several times over the course of a few weeks additional light layers of ash covered the area. The scattered rains continued to make a mud that left distinct impressions. Finally a heavy ash fall buried the area deeply, protecting the Footprint Tuff from erosion. Over time, the ash cemented and became rock. Weathering eventually brought the Footprint Tuff layer to the surface again, giving modern man a unique view of a specific event in the life of early hominids. A brief moment in prehistoric time has been preserved.
Jill M. Church
See also Anthropology; Dating Techniques; Evolution, Organic; Fossils, Interpretations of; Olduvai Gorge; Paleontology
Hay, R. L., & Leakey, M. D. (1982). Fossil footprints of Laetoli. Scientific American, 246, 50-57.
Leakey, M. D., & Harris, J. M. (Eds.). (1987). Laetoli: A Pliocene site in northern Tanzania. Oxford, UK: Clarendon.
Stringer, C., & Andrews, P. (2005). The complete world of human evolution. New York: Thames & Hudson.