In 2008, paleoanthropologists reveled in the discovery of a new species of human ancestor, one that held the promise of filling in an important piece of the puzzle of human evolution. Dubbed Australopithecus sediba, this hominin species was described from a pair of partial skeletons representing both sexes, skeletons found in a Malapa cavern near Johannesburg — South Africa’s “Cradle of Humankind” site.

Uncovered by 9-year-old Mattew Berger after he tripped on a bizarre-looking rock while out walking with his dog, the specimens were dated to 2 million years ago and sparked a long debate among paleoanthropologists, who couldn’t agree on how to classify the fossils. As a result, the bones remained shrouded in mystery for the past decade, as some scientists suggested that Australopithecus sediba belonged to an already known hominin species — while others argued that the remains actually pointed to not one, but two unknown species.

Now, the 2-million-year-old fossils have been confirmed as a “missing link” in the history of the human species, CNN is reporting. After much consideration, researchers have finally agreed that Australopithecus sediba is not only a distinct species, but actually represents a bridge between Australopithecus africanus and Homo habilis.

According to the Human Origins website of the Smithsonian National Museum of Natural History, Australopithecus africanus was an ape-like hominin — and the oldest known early human from South Africa. Meanwhile, Homo habilis was one of the earliest members of the genus Homo and, though it retained some ape-like features, it was proficient in using tools some 1.5 million years to 2 million years ago, notes the Huffington Post.

The new conclusion about Australopithecus sediba is detailed in a study in the journal Paleoanthropology, which published a special issue on the early human species featuring data from nine separate studies. These papers each examine different sections of the hominin’s skeletal anatomy, while also providing descriptions of body size and proportions — as well as a detailed look into the species’ walking mechanics, reports Phys.org.

“The researchers find that Au. sediba is in fact a unique species, refuting earlier critics who questioned its validity as a species,” states the media outlet.

“Au. sediba is distinct from both Australopithecus africanus, with which it shares a close geographic proximity, and from early members of the genus Homo (e.g., Homo habilis) in both East and South Africa; yet, it also shares features with both groups, suggesting a close evolutionary relationship.”

Facial Reconstruction of 'Australopithecus sediba.' Featured image credit: Cicero Moraes et alii Wikimedia Commons/Resized(CC BY 4.0 )

For instance, some details regarding the teeth, the length of the arms and legs, and the narrow upper chest of Australopithecus sediba are similar to fossils of earlier Australopithecus. However, other tooth traits of the 2-million-year-old skeletons — as well as the fossils’ broad lower chest — resemble features seen in the Homo genus.

Moreover, the hands of Australopithecus sediba also had grasping capabilities that were even superior to those of Homo habilis, which suggests that the hominin was an early tool-user, too. In addition, the research also includes a 3D computer animation illustrating the unusual way in which Australopithecus sediba walked, with its foot turned inward and the weight focused on the outer edge of the foot.

This revelation that Australopithecus sediba is actually the missing link between early humans and our more ape-like ancestors suggests that we were still swinging from trees 2 million years ago. As the new study point out, all three species “spent significant time climbing in trees, perhaps for foraging and protection from predators.”

“The combination of primitive and derived traits in Australopithecus sediba shows part of the transition from a form adapted to partial arboreality to one primarily adapted to bipedal walking. but the legs and feet point to a previously unknown way of walking upright,” details the Human Origins website.

In addition, Australopithecus sediba helps fill a gap in the timeline of human evolution, as the hominin species slides in between the famous “Lucy,” the 3.2-million-year-old Australopithecus afarensis female unearthed in 1974 in Ethiopia, and Homo habilis, nicknamed the “handy man.”

Comparison of ‘Lucy’s’ skeleton (center) to two of the two ‘Australopithecus sediba’ hominins found in Malapa. Featured image credit: Profberger Wikimedia Commons/Resized(CC BY-SA 3.0 )

“This larger picture sheds light on the lifeways of Au. sediba and also on a major transition in hominin evolution,” said lead researcher Scott Williams of New York University.