A mysterious bipedal hominid left its footprints more than three million years ago in Tanzania

Half a century ago, the paleontologist Mary Leakey and his team discovered five consecutive footprints at the Laetoli site in Tanzania, providing the oldest unequivocal evidence of bipedalism in hominids. At the time, it was proposed that these footprints had been made by Australopithecus afarensis, the same species as the famous ‘Lucy’ skeleton.

Yet another set of footprints excavated in a nearby site called A, and later covered, aroused a debate. At first, some researchers thought they must be of a type of hominid, others that they belonged to a young bear who walked on their hind legs. In the 1980s, the geologist Dick hay, a member of Mary Leakey’s research team, dated them to 3.7 million years old using the relationship between radioactive potassium and argon (K-Ar dating) in the volcanic ash layer.

In 2019 these tracks were re-excavated and completely cleaned by a team of scientists displaced to Tanzania. The footprints were measured, photographed and 3D scanned.

Although thousands of animal fossils have been found at Laetoli, none were of bears. In this way, they unequivocally determined that they were made by a hominid.

Footprints are very different in bears, chimpanzees, and humans. By analyzing them, the researchers were able to verify that they were very similar to those of hominids. In fact, they came to analyze on video the behavior of the wild american black bear (Ursus americanus), which barely walks on its hind legs. Furthermore, although thousands of animal fossils have been found in Laetoli, none were bear. In this way, they unequivocally determined that they were made by a hominid, but which one?

“These footprints show that the evolution of the upright gait was more complicated and more interesting than we thought. In this age of our evolutionary history there were at least two hominids that walked differently, with differently shaped feet. This shows that the acquisition of human gait was less linear than many imagine. In other words, throughout our history, there have been different evolutionary experiments on how to be biped”, Declares to SINC Jeremy M. De Silva, co-author of the work, which publishes the magazine Nature, and researcher at Dartmouth College (USA).

A curious way of walking crossed

This hominid, which has not yet been identified, walked in an unusual way: his step was crossedthat is, each foot crosses above the midline of the body to touch the ground in front of the other foot.

There is evidence that different hominin species walked in different biomechanical ways, but there is no reconstructed cross walk like this one.

There is evidence that different hominin species walked in different biomechanical ways, but there is no reconstructed cross-walking like this

“We are still not sure what it means. Cross-gait sometimes occurs in humans when we walk on uneven ground, which perhaps explains this strange gait. Or maybe just this individual hominin walked in a peculiar way. Or maybe an unknown species of hominin was adapted to walk this way. We will see it as more traces are discovered ”, assures De Silva.

Ellison J. McNutt, a scientist from the University of Ohio (USA), who is also participating in the study, explains that although humans do not usually take crossed steps, this movement may have occurred when trying to reestablish the Balance: “The tracks from site A may have been the result of a hominid walking through an area that was an uneven surface.”

“We cleaned the inside of the tracks and found a clear impression of a big toe of the enlarged foot, something that is only found in primates, including apes and hominins, ”continues De Silva.

The anatomy of hip and knee prevents bears from balancing easily on one leg. When they walk on two they wobble from side to side, producing widely spaced footprints. Yet another proof that the path made by these fossil tracks is too narrow to come from these animals.

Different footprint from Lucy’s

The team also compared the footprints from Site A and inferred foot proportions, morphology, and likely gait. Thus they showed that they were different from those of Australopithecus afarensis of the G and S fields.

There are fascinating differences in shape between the tracks from Site A and those (presumably) of A. afarensis from Sites G and S

J. De Silva

“There are fascinating differences in shape between the footprints from Site A and those (presumably) from A. afarensis of the G and S reservoirs. The former are much wider for their length and have a slightly more divergent big toe. In fact, in our analysis, the fingerprints of A are so different from the fingerprints of A. afarensis as is a chimpanzee footprint of a human footprint ”, the expert concludes to SINC.

These findings are part of a growing body of evidence pointing to an undervalued diversity of hominids from this era.


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