Footprints from Laetoli Analyzed

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December 19, 2021

In 1978, a team led by Mary Leakey uncovered several trackways of animal foot prints at a site in Tanzania called Laetoli. There were bird and other animal footprints but what caught everyone's attention were prints that appeared to be human. Some trackways containing the human foot prints were 60 feet in length, some were as short as 5 feet. The trackways were identified as Trackway A through H. Trackway G was the longest at 60 feet and Trackway A at 5 feet was quickly covered over to preserve the foot prints.

What caused the foot prints was this: a nearby volcano erupted  and covered the area with a fine ash. Sometime later, many animals, including quadrupeds and bipeds, walked through the ash. Later still, perhaps a few hours or a few days, a light rain fell. The rain was not so forceful as to wash the footprints and ash away but strong enough to set the ash as if it were concrete, thus preserving the foot prints of the many animals who had walked through the ash.

Because this was volcanic ash, the site could be dated radiometrically by the Leakey team to 3.66 million years ago. The type specimen for Australopithecus afarensis had been found at Laetoli and the human appearing footprints were attributed to that species. The famous fossil “Lucy", found by Donald Johanson more than 700 miles away in Ethiopia, was A. afarensis as well and anatomically an obligate biped. The Laetoli foot prints caused many paleoanthropologists, formerly skeptical of the claims of bipedality, to accept those claims.

In the journal Nature for December 1 there is a paper by McNutt et al. discussing trackway A at Laetoli, which they re-excavated and bearing the same estimated date - 3.66 ma - as the other track weighs, and claiming the possibility the footprints recorded there were made by another bipedal species. Dr. Yohannes Halle-Selassie, Director of the Institute of Human Origins as well as a professor at the School of Human Evolution & Social Change (SHESC) at Arizona State University comments "I don't think many paleoanthropologists would find these 'footprints' as convincing as the Laetoli G1 trackway. ...using this as evidence for the presence of two hominin species at Laetoli would be a steep hill to climb, especially when all of the fossil hominin specimens discovered at Laetoli thus far belong to one species, A. afarensis.”

The McNutt et al. paper can be found here. A companion piece in the same issue of Nature  can be found in the same journal.