Ancient human relative walked like a human but climbed like an ape, new fossils suggest - CNN

"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 only the best-preserved hominin lower back ever discovered, but also probably the best preserved," said Professor Lee Berger, an author on the study and leader of the Malapa project.

The excellent preservation of Issa helped to show that curvature of sediba's spine was more extreme than any other Australopithecus yet discovered -- that kind of spine curvature is typically seen in modern humans and demonstrates strong adaptations to bipedalism.

"While the presence of lordosis (the inward curve of the lumbar spine) and other features of the spine represent clear adaptations to walking on two legs, there are other features, such as the large and upward oriented transverse processes, that suggest powerful trunk musculature, perhaps for arboreal behaviors," said Professor Gabrielle Russo of Stony Brook University, another author on the study.

Arboreal behaviors refer to climbing and living in trees.

"The spine ties this all together," added study author Professor Thomas Cody Prang of Texas A&M University, who studies how ancient hominins walked and climbed.

"In what manner these combinations of traits persisted in our ancient ancestors, including potential adaptations to both walking on the ground on two legs and climbing trees effectively, is perhaps one of the major outstanding questions in human origins."

The study concluded that Australopithecus sediba was a transitional form of ancient human relative and its spine is clearly intermediate in shape between those of modern humans and great apes -- meaning that the species would have possessed both human and ape-like traits in its movements.

The study was published Tuesday in the journal e-Life.