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Australopithecus sediba walked like a human, but climbed like an ape

Daniel García Martínez , from the Anthropology Unit of the Complutense University of Madrid ( UCM ) and affiliated member of the National Research Center on Human Evolution ( CENIEH ) is part of the international team of scientists that has just published in the magazine e-Life the discovery of fossil vertebrae two million years old antiquity of an extinct species , Australopithecus sediba .

These vertebrae resolve a decades-long debate by showing that early hominids used their upper extremities to climb like apes and their lower extremities to walk like humans.

The recovery in a rock of new vertebrae of the spinal column of a single individual of Australopithecus sediba, found in 2015 at the Malapa site (Johannesburg, South Africa), together with the vertebrae discovered in 2008, they form one of the most complete lumbar columns in the fossil record and provide insight into how this ancient human relative walked and climbed.

The first hominids used the upper extremities to climb like apes and the lower ones to walk like humans

The discovery also establishes that, like humans, sediba had only five lumbar vertebrae . “The lumbar region is critical to understanding the nature of bipedalism in our earliest ancestors and to understanding how well adapted they were to walking on two legs,” explains Scott Williams , lead author of the study.

One of the most complete skeletons

The fossils were virtually reconstructed, after being scanned using computed microtomography – method of analysis by X-rays where the internal and external image of an object are represented in 3D -, thus eliminating the risk of damaging the delicate bones.

Once virtually reconstructed, the vertebrae were added to previously recovered fossils, which perfectly articulated with the vertebral column of the fossil skeleton MH 2 , part of the original type specimens from [19459007 ] Australopithecus sediba first described in 2010.

The female skeleton MH 2, nicknamed by researchers as Issa (‘protector’ in Swahili), is one of the two first hominid skeletons that conserve both a relatively complete lower column and the dentition of the same individual, which allows us to be certain about the species to which the vertebral column belongs.

Issa is one of the first two hominid skeletons to preserve both a relatively complete lower spine and the dentition of the same individual

“While Issa was already one of the most complete skeletons of an ancient hominin ever discovered, now these vertebrae complete the lower back and make his lumbar region a competitor, not just for the hominid. most complete, but also probably the best preserved. This combination of integrity and preservation gave the team an unprecedented look at the anatomy of the species’ lower back, ”says Lee Berger , study co-author and Malapa project leader.

Transitional hominid

According to this work, lordosis of Australopithecus sediba -excessive curvature lower back – is more extreme than that of any other Australopithecus discovered so far, surpassed only by that observed in the spine of the Turkana boy ( Homo erectus ) in Kenya, of 1.6 million years, and some modern humans.

Regarding the integration of the lumbar spine with other regions of the skeleton, García Martínez indicates that “the ability to use the arboreal environment for locomotion is also observed in some other anatomical regions, such as for example in his narrow upper thorax ”.

Australopithecus sediba walked like a human, but climbed like an ape

Sediba is a transitional form of an ancient human relative and its spine is clearly intermediate in shape between modern humans (and Neanderthals) and great apes

Lee Berger, study author

Australopithecus sediba walked like a human, but climbed like an ape

“These results from sediba fit very well with our other torso reconstructions of transitional hominins , where we also see mosaic evolution in other related anatomical systems”, points out Markus Bastir , from the National Museum of Natural Sciences ( MNCN ).

Previous studies on the upper extremities, pelvis, and lower extremities of this ancient species already noted mixed adaptations through the skeleton in sediba indicating its transitional nature between walking as a human and climb like an ape.

Sediba is a transitional form of an ancient human relative and its spine is clearly intermediate in shape between modern humans (and Neanderthals) and great apes. Issa walked like a human, but he could climb like a monkey ”, concludes Berger, who in 2008, together with his nine-year-old son, Matthew, discovered the first remains of what would become this new species .

Reference:

Williams et al. “New fossils of Australopithecus sediba reveal a nearly complete lower back.” eLife .

Rights: Creative Commons.

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