Daniel Garcia Martinez, from the Anthropology Unit of the Complutense University of Madrid (UCM) and affiliate member of the National Center for Research on Human Evolution (CENIEH) is part of the international team of scientists that has just published in the journal e-life the discovery of fossil vertebrae two million years of an extinct species, Australopithecus sediba.

These vertebrae resolve a decades-long debate, showing that the first hominids they used their upper limbs to climb like apes and their lower limbs to walk like humans.

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

Early hominids used the upper extremities to climb like apes and the lower extremities to walk like humans.

The discovery also establishes that, like humans, Sediba there was only five lumbar vertebrae. “The lumbar region is essential to understand the nature of bipedalism in our early ancestors ​​and understand how well adapted they were to walk on two legs, he explains. Scott Williams, lead author of the study.

One of the most complete skeletons

The fossils were virtually reconstructed, after being digitized by computed microtomography –Radiographic analysis method in which the internal and external image of an object is represented in 3D– in order to eliminate the risk of damaging delicate bones.

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

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

Issa is one of the first two hominid skeletons to retain a relatively complete lumbar spine and teeth from the same individual.

“If Issa was already one of the most complete skeletons of an ancient hominid ever discovered, now these vertebrae complete your lower back and make your lower back a competitor to not just the most complete hominid but probably the best preserved. This combination of integrity and preservation gave the team unprecedented insight into the anatomy of the species’ lower back,” he says. Lee Berger, co-author of the study and leader of the Malapa project.

transitional hominid

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

As for 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 the narrow upper thorax”.

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

Lee Berger, study author

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

Previous studies of the upper extremities, pelvis, and lower extremities of this ancient species have already observed mixed adaptations across the skeleton in Sediba indicating its transitional nature between walking like a human and climbing like an ape.

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

Reference:

Williams et al. “New fossils of Australopithecus sediba reveal an almost complete lumbar region”. eLife.

Rights: Creative Commons.

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