Traveling from branch to branch, with the agility of apes, was something the first Homo could still do. They have just found the fossil remains of a human ancestor who walked like a human but climbed like an ape.

Evolution required leaving things behind. A first-class brain, capable of imagining, worshiping gods or playing football, became possible after millions of years of profit and loss. One of the most considerable “losses” is the athletic anatomy that monkeys still possess, which allows them, among other great things, to fly from branch to branch.

The first species of Homo had to adapt to a new way of moving, down to earth, but for millions of years they retained both abilities, walk and climb.

A study involving the CSIC discovered fossil vertebrae in the lumbar spine of Australopithecus sediba, an ancient human relative who once walked bipedal but still climbed branches like an ape,

two million years ago

An international team with the participation of researchers National Museum of Natural Sciences (MNCN-CSIC), discovered two million years of fossil vertebrae of Australopithecus sediba, an extinct species of an ancient human relative. The retrieval of new lumbar vertebrae from the lumbar spine of a single individual from this ancestor of modern humans, together with previously discovered vertebrae, form one of the most complete lumbar spines in the fossil record and give an idea of ​​how this ancient human relative walked. and climbed. The study was published in the open access journal e-Life.

The fossils were discovered in 2015 during the excavations of a mining route accompanying the Malapa site, the Cradle of the World Heritage Site, located northwest of Johannesburg, South Africa. Malapa is also where, in 2008, the University of the Witwatersrand professor Lee Berger and his nine-year-old son, Matthew, discovered the first remains of what would become a new species of ancient human relative called Australopithecus sediba.

Anatomical position of the new A. sediba fossils in the complete skeleton and virtual reconstruction (the new lumbar vertebrae in red)

To eliminate the risk of damaging the delicate bones with your hands, the fossils were prepared virtually after being digitized at the University of the Witwatersrand. The vertebrae were then added to fossils recovered during the earlier work. Scientists have found that they articulate perfectly with the backbone of the fossil skeleton, that is, with part of the original Australopithecus sediba specimens first described in 2010.

The discovery also established that, like humans, sediba had only five lumbar vertebrae. “The lower back is critical to understanding the nature of bipedalism in our early ancestors and to understanding how well they were adapted to walking on two legs,” said Professor Scott Williams of New York University and Wits University and lead author of the article.

One of the most complete skeletons of an ancient hominid

The researchers dubbed the female skeleton “Issa”, which means protector in Swahili. The discovery of the new specimens means that Issa now becomes one of the first two hominid skeletons to retain a relatively complete lumbar spine and dentition from the same individual, allowing certainty as to which species the spine belongs to.

“Although Issa was once one of the most complete skeletons of an ancient hominid ever discovered, these vertebrae virtually complete the lower back and make Issa’s lower back a contender not only for the best preserved hominid ever discovered, but also probably the best preserved ,” says Berger, author of the study and leader of the Malapa project. “This combination of integrity and preservation gave the team unprecedented insight into the anatomy of the species’ lower back,” he adds.

The study also shows that sediba lordosis was even more extreme than any other australopithecine discovered so far. In fact, the degree of spinal curvature observed was only surpassed by that observed in the spine of the Turkana boy (Homo erectus) from Kenya, 1.6 million years ago, and from some modern humans.

About the integration of the lumbar spine with other regions of the skeleton, researcher Daniel García Martínez, from the Anthropology Unit of the Complutense University of Madrid and affiliated member of CENIEH, indicates: “the ability to use the arboreal environment for locomotion is also observed in some other anatomical regions, such as your narrow upper thorax”. “These sediba results fit very well with other transitional reconstructions of the torso of hominins from our research project that we have at MNCN, where we also see mosaic evolution in other related anatomical systems,” adds Markus Bastir.

In previous studies carried out with this ancient species, mixed adaptations were highlighted throughout the sediba skeleton, which indicates its transitional nature between walking like a human and adaptations to climbing. This includes features studied in the upper extremities, pelvis and lower extremities.

The results show that sediba is a transitional form of an ancient human relative and its spine is clearly intermediate in form between modern humans (and Neanderthals) and great apes. ‘Issa walked like a human, but could climb like an ape,’ concludes Berger.

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