The missing link? South African fossils reveal a creature with ape and human characteristics

Is this the missing link?

A group of researchers have put together the most complete picture yet of Australopithecus sediba, an early hominin that lived in southern Africa nearly two million years ago. Their findings appear in six separate papers published in the latest edition of the journal Science.

Anthropologist Lee Berger of the Evolutionary Studies Institute at the University of Witwatersrand in Johannesburg, South Africa, and his colleagues studied the fossilized remains of two hominin individuals discovered at the site of Malapa, located about 30 miles from Johannesburg. Hominins make up the group consisting of modern humans, extinct human species, and all their immediate ancestors, while hominids consist of all modern and extinct Great Apes (chimpanzees, gorillas, orangutans, and their immediate ancestors).

Williams and his colleagues describe Au. sediba’s vertebral column, analyzing the creature’s cervical, thoracic, lumbar, sacral regions. The researchers based their analysis on two partially complete spinal columns and reveal that while Au. sediba had a lower back with a distinctly human-like curvature, it was longer and more flexible than that seen in modern humans. According to Williams, Au. sediba displayed a “compromise form” of bipedalism, suggesting a creature that still spent some of its time climbing trees.

The researchers also analyzed Au. sediba’s dental characteristics and rib cage, as well as its upper and lower limb bones. In the series of papers, researchers concluded that although the species is close to Au. africanus, it represents a southern African autralopith clade, or branch, distinct from east African australopiths. This finding has important implications for understanding the hominin evolutionary position through the end of the Pliocene Era.

Analysis of Au. sediba’s upper and lower limb bones reveal a creature whose upper torso resembled an ape while its lower body looked more like a human. Like other australopiths, Au. sediba had upper limbs that were well-suited for climbing trees, while its lower limb anatomy showed that it was able to walk with exceptional precision. The description of the animal’s rib cage indicates that it had a distinctly ape-like ‘shrugged’ shoulder appearance.

According to Berger, the Malapa fossils provide researchers with an “unprecedented insight” into the anatomy and evolutionary position of one of our early human ancestors. Calling Au. sediba “mosaic in its anatomy,” he noted that it presented a picture of a creature that was different both from other australopiths and from early humans.

“Such clear insight into the anatomy of an early hominin species will clearly have implications for interpreting the evolutionary processes that affected the mode and tempo of hominin evolution and the interpretation of the anatomy of less well preserved species,” said Berger.

The studies themselves represent the most comprehensive depiction of the earliest human ancestral remains ever discovered. Experts around the world say it is on par with the studies examining Lucy, an individual  Australopithecus afarensis. The study could provide insight into how the first humans evolved over time and eventually how they moved from Africa to Asia and Europe, say researchers.