Issa climbed like a monkey and walked like a human

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Issa climbed like a monkey and walked like a human

Reconstruction of Issa's appearance.

The unearthing of fossilized vertebrae from the lower back of an Australopithecus sediba establishes that these hominins, who lived 2 million years ago, used their upper limbs to climb like apes and their lower limbs to walk like humans.

The newly discovered lumbar vertebrae […] constitute one of the most complete lower backs ever found in early hominids and provide insight into how this ancient relative of humans walked and climbed, explains the University of the Witwatersrand in a press release.

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Silhouette of Australopithecus sediba showing newly discovered with other skeletal bones of the species.

Paleontologists from 17 institutions participated in work published in the journal eLife (in English) describing the new fossils. These vertebrae are, according to scientists, the missing link that settles an old debate on the mode of locomotion of this ancient species.

These fossils were discovered in 2015, during excavations that took place at the fossiliferous site of Malapa, located in South Africa in the area of ​​the sites of the cradle of humanity, listed as World Heritage of Humanity .

It was at this site that paleontologist Lee Berger of the University of the Witwatersrand discovered the first remains of an Australopithecus sediba in 2008, which he described in an article published in 2010.

The new vertebrae were recovered from breccias, conglomerates of rocks resulting from the mechanical degradation of ;other rocks.

The lumbar region is essential for understanding the nature of bipedalism in our oldest ancestors and for knowing the extent to which they were adapted to walking on two legs, explains in the press release Professor Scott Williams of the University of the Witwatersrand, the lead author of the paper.

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Reconstruction of Issa's appearance on display at the University's Museum of Natural History from Michigan.

Lumbar vertebral series are extraordinarily rare in the hominid fossil record, and only three comparable lower spines are known in the entire early African record, continues the scientist.

The female skeleton bears the catalog number MH2, but the researchers nicknamed it Issa, which means protector in Swahili.

This discovery also established that, like humans, Australopithecus sediba had only five lumbar vertebrae. Issa is one of only two early hominid skeletons to possess both a lower spine and relatively complete dentition.

These vertebrae virtually complete his lower back and make Issa's lumbar region the best-preserved ever discovered, said Lee Berger, who is one of the study's authors and the head of the study. Malapa project.

Previous analyzes of the species' incomplete lower spine, by authors not involved in the present study, supported the hypothesis that the spine of s edibawas relatively straight, with no curvature, or lordosis, commonly seen in modern humans and associated with bipedalism.

Furthermore, these scans suggested that the spine of Australopithecus sediba more closely resembled that of extinct species of Neanderthals and other more primitive species of ancient hominins.

However, the recent discovery reveals that Issa's lordosis was in fact more extreme than that of all other australopithecines discovered to date, and that the extent of spinal curvature observed was not exceeded than that seen on the spine of Turkana man (Homo erectus) from Kenya, 1.6 million years old, and some modern humans.< /p>

While the presence of lordosis and other features represents an obvious adaptation to walking on two legs, other features suggest powerful trunk musculature, possibly associated with arboreal behaviors, explains Prof. Gabrielle Russo of Stony Brook University, which also participated in the study.

Strong upward-pointing transverse spines are usually a sign of powerful trunk musculature, as seen in great apes, adds Professor Shahed Nalla of the University of the Witwatersrand. Combined with other parts of the torso anatomy, this indicates that the sediba retained clear adaptations for climbing.

Other work conducted on this ancient species have shown mixed adaptations of its skeleton, which tends to show its transitional nature between walking like a human and adaptations to climbing. These include distinguishing features in the upper and lower limbs, but also the pelvis.

The spine connects it all, concludes Professor Cody Prang of the Texas A&M University.

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