Friday, August 12

The human ancestor who walked like us but climbed like an ape

A group of researchers has discovered fossil vertebrae two million years old. Australopithecus sediba, an extinct species of an ancient human relative. The recovery of new lumbar vertebrae from the spine of a single individual from this ancestor of modern humans, together with previously discovered vertebrae, form one of the most complete lumbar columns in the fossil record and give insight into how this ancient human relative walked and climbed.

The study, in which researchers have participated National Museum of Natural Sciences (MNCN-CSIC), has been published in the open access journal e-Life.

The fossils were discovered in 2015 during the excavations of a mining route that runs alongside the Malapa site, the Cradle of Humankind World Heritage, located northwest of Johannesburg, South Africa, iinforms the CSIC in a press release.

Berger and his son

Malapa is also the place where, in 2008, Professor Lee Berger of the University of the Witwatersrand and his nine-year-old son, Matthew, discovered the first remains of what would be a new species of ancient human relative called Australopithecus sediba.

“The fossils at the site date from approximately two million years before the present. The vertebrae described in the present study were recovered with virtual morphology tools in a consolidated, cement-like rock, known as a breccia, in near-joint”, explains Markus Bastir. , a researcher at the MNCN-CSIC and one of the authors of the study together with scientists from the University of New York (USA), the University of the Witwatersrand (South Africa) and the Complutense University of Madrid.

To eliminate the risk of damaging the delicate bones by hand, the fossils were prepared virtually after scanning at the University of the Witwatersrand. The vertebrae were then added to the fossils recovered during the previous work.

The scientists found that they articulated perfectly with the backbone of the fossil skeleton, that is, with part of the original type specimens of Australopithecus sediba described for the first time in 2010.

The discovery also established that, like humans, sediba had only five lumbar vertebrae. “The lumbar region is critical to understanding the nature of bipedalism in our early ancestors and to understanding how well adapted they were to walking on two legs,” says 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

Researchers have nicknamed 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 hominin skeletons to retain both a relatively complete lower spine and a dentition from the same individual, allowing for certainty as to which species the spinal column belongs to.

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

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

Regarding 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 an affiliate member of CENIEH, indicates: “the ability to use the arboreal environment for locomotion it is also seen in some other anatomical regions, such as his narrow upper thorax. ”

“These sediba results fit very well with other transitional hominin torso reconstructions from our research project that we have at the MNCN, where we also see mosaic evolution in other related anatomical systems,” adds Markus Bastir.

From walking like a human to climbing adaptations

In previous studies carried out on this ancient species, mixed adaptations throughout the sediba skeleton have been highlighted that have indicated its transitional nature between walking like a human and climbing adaptations. These include features studied in the upper extremities, pelvis, and lower extremities.

The results demonstrate that 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 could climb like a monkey, “Berger concludes.