Fossil footprints hint at mystery hominin with unusual walking style

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A acceptable of 3.7-million-year-old footprints were initially thought to person been near by a carnivore walking upright, but person present been reinterpreted arsenic the prints of an unidentified hominin that walked a small spot similar a modern catwalk manner model

Humans 1 December 2021

By Michael Marshall

Detail of a azygous  big  footprint from the way   of fossilised hominin footprints

One of the hominin footprints preserved astatine Laetoli successful Tanzania

Science Photo Library

Ancient footprints that were primitively thought to person been made by a carnivore walking connected 2 legs were really made by an extinct quality species. The find means determination are present 3 known sets of hominin footprints from the aforesaid locale successful Tanzania.

It isn’t wide which hominin taxon made the prints. The authors of the caller survey accidental they don’t lucifer the different sets of footprints astatine Laetoli, a tract successful Tanzania, truthful were astir apt made by a antithetic species. If this is true, it would mean that 2 hominin taxon coexisted successful the aforesaid portion astatine the aforesaid time.

“Not lone are they not a bear, they are hominin and they are not the aforesaid hominin arsenic those that made [the different footprints],” says Ellison McNutt astatine Ohio University Heritage College of Osteopathic Medicine successful Athens.

The footprints were discovered successful 1976 by Peter Jones and Philip Leakey. Excavating astatine Laetoli, they recovered 5 prints successful a spot they dubbed tract A. The tracks had been near successful brushed volcanic ash that subsequently hardened into rock.

The pair’s workfellow Mary Leakey suggested that the prints had been near by a hominin. However, aboriginal studies suggested that they were really made by a carnivore walking connected its hind legs. As a result, tract A fell into obscurity.

Meanwhile, more footprints were recovered astatine Laetoli successful a determination a fewer kilometres away, labelled tract G, and these were definitely made by hominins. The way stretches 24 metres and includes prints (one of which is pictured above) from 3 individuals walking together. Both sets of footprints are 3.66 cardinal years aged and are thought to person been made by Australopithecus afarensis, the taxon to which the celebrated Lucy fossil belonged.

Now, McNutt and her colleagues person re-excavated the tract A footprints. “The carnivore proposal was precise tenable astatine the time,” she says, due to the fact that the prints bash look unusual. But the sediment successful them was ne'er decently cleaned out, truthful their existent signifier wasn’t known. McNutt’s squad cleaned the prints thoroughly and produced 3D scans of them.

The researchers compared the tracks from tract A with footprints made by humans, chimpanzees and American achromatic bears. “There are a batch of things that marque it distinctly hominin,” says McNutt. For example, the large toes were proportionally overmuch larger than the 2nd toes, which is seen successful hominins but not successful bears.

The squad was “very clever” to re-excavate tract A and “it’s rather convincing that it’s not a bear”, says Marco Cherin astatine the University of Perugia successful Italy. “I deliberation it astir decidedly is simply a hominin.”

McNutt and her colleagues besides reason that the prints don’t lucifer the much celebrated tracks astatine tract G, truthful were truthful made by a antithetic taxon of hominin. For instance, idiosyncratic footprints astatine tract A were comparatively wide for their length, compared with those astatine tract G. The hominin besides seems to person cross-stepped, meaning it brought its feet crossed its body’s cardinal enactment – a gait seen successful its astir exaggerated signifier erstwhile manner models locomotion down runways placing 1 ft straight successful beforehand of the other.

“It’s not afarensis,” says McNutt. “It is surely Australopithecus oregon thing precise similar it.” Beyond that, she says we can’t beryllium sure. However, she adds that elsewhere successful Africa, determination is wide grounds of aggregate hominin taxon coexisting successful the aforesaid regions, truthful it wouldn’t beryllium astonishing if the aforesaid was existent astatine Laetoli.

Cherin isn’t convinced astir that. “For the moment, I would beryllium astir cautious astir the anticipation of having 2 hominin track-makers successful Laetoli,” helium says.

In 2016, Cherin’s squad described two further hominin trackways astatine Laetoli, astatine a spot called tract S. These were interpreted arsenic belonging to A. afarensis, but they are a scope of sizes, and Cherin says the tract A prints don’t look precise antithetic successful presumption of their size and signifier from the tract S prints, which mightiness suggest they were each near by members of the aforesaid species. He highlights a survey published successful July that shows it is indispensable to person much than 20 prints to get a reliable representation of however an carnal walked. There are lone 5 prints astatine tract A.

Journal reference: Nature, DOI: 10.1038/s41586-021-04187-7

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