Enigmatic 3.6 million-year-old footsteps

Bears in Africa? They survived there, in the Atlas, until very recently, and fossils 5 million years old have been unearthed in particular in the Langebaanweg quarry, in South Africa. But were they present in Tanzania, 3.66 million years ago, sharing the territory of Australopithecus Lucy and its congeners? The hypothesis, mentioned in the 1970s, to explain the enigmatic fossilized footsteps found on the Laetoli site, “Pulled a little by the hair of the bear”, according to paleontologist Yves Coppens, may have just died his beautiful death.

It has in fact been re-examined by a large international team, returned in 2019 to the scene to make new surveys of “track A” which has preserved the suspicious footprints, covered at the end of the 1970s to protect them from erosion. and the passage of livestock. In the review Nature of December 2, Ellison McNutt (University of Southern California, Los Angeles) and colleagues suggest that these traces may have been left there by an undetermined species of hominin, distinct from the australopithecines already identified in the region.

The Laetoli site is well known in the paleontological community for its richness in various fossils – it was explored in the 1930s by the pioneer of African excavations Louis Leakey. It was there that his wife Mary was discovered in 1974, a mandible called LH 4 ​​(for Laetoli Hominid 4) which will serve as a specimen to define the species. Australopithecus afarensis, to which the famous Lucy belongs.

Swaying approach

It was also there that in 1976, according to legend, paleontologist Andrew Hill literally found his nose on fossil footprints, when he had just tripped while trying to avoid an elephant dung that a colleague had joked to him. No less than 18,400 animal tracks were to be unveiled, printed in three dimensions in volcanic ash and protected by successive eruptions, 3.66 million years ago. Among them, Mary Leakey’s team identifies five consecutive footprints which, according to her, are the mark of the passage from a bipedal hominin to the swaying gait: the successive traces seemed to pass on the opposite side of the axis of movement of the ‘individual – “A bit like those models who cross their footsteps during fashion shows”, describes Yves Coppens.

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The Frenchman, who first visited Laetoli in 1963, remembers the jokes with his colleagues about the enigmatic move. “The British said it was an Australopithecus hopped around to piss off paleontologists, and we were talking more about an early invention of wine …” But two years later, in 1978, the discovery of new, less equivocal footprints, clearly bipedal and attributed to A. afarensis, those of “track G”, eclipses the first. The hypothesis of the passage on “track A” of a bear on its hind legs then takes shape. A print of a right bear’s foot corresponding more or less to that of the left foot of a hominin, no need to explain the strange crossing of steps along the line of progression. It doesn’t matter if there are no fossil bears in Laetoli, Agriotherium africanum discovered at the same time in South Africa, even if it is older, will do the trick, without totally winning the membership. And then, with time passing, as Stephanie Melillo (Max-Planck Institute for Evolutionary Anthropology Leipzig) nicely writes, in a commentary in Nature, “The footprints of the track A were more easily forgotten than explained “.

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