Ancient Apes May Have Learned To Walk Upright In The Trees

Ancient Apes May Have Learned To Walk Upright In The Trees

Scientists in Germany have discovered the fossilised remains of a previously unknown ancient ape with an unusual way of moving through the treetops. By standing upright on two feet and grasping branches with its long arms, this animal may have set an important evolutionary precedent for the bipedal primates that followed.

The ability to stand upright and walk on two feet may have emerged as a physical trait not in Africa as is commonly assumed, but in Europe, according to new research published today in Nature. The authors, led by paleontologist Madelaine Böhme from Eberhard Karls University of Tübingen, describe an entirely new species of ape, named Danuvius guggenmosi. This creature—possibly a distant ancestor to humans—lived 11.2 million years ago in what is now southern Germany, an area that once featured a lush forest.

Artist’s impression of Danuvius. (Illustration: Velizar Simeonovski)

Remarkably, the bones of Danuvius suggests it was capable of using all four limbs while climbing, but it did so while walking upright on two legs—an unprecedented form of locomotion the researchers describe as “extended limb clambering.” This method of manoeuvring through an arboreal landscape has never been documented before, and the authors say it could represent an important evolutionary adaptation that set the stage for ground-based bipedal locomotion.

Scientists have struggled to explain how apes transitioned to fully upright, two-legged walking. Much of this has to do with the lack of fossil evidence and the various modes from which this ability may have emerged. Bipedalism may have sprung from quadrupedal monkey-like apes that suspended themselves from branches, from brachiating apes that used their limbs to swing from branch to branch (like orangutans), or from so-called knuckle-walking apes, also known as terrestrial quadrupeds (similar to modern chimps and gorillas). The new paper proposes a previously unknown mode of locomotion that could finally explain this important transition.

The new fossils were excavated between 2015 and 2018 at the Hammerschmiede Clay pit in Bavaria, Germany. The fossils were in reasonably good shape, but some bones were crushed by machinery used at the site, which is an active clay mine. The sedimentary layer from which the fossils were pulled were dated to around 11.62 million years ago—within the Miocene Epoch, when the ancestors of humans and apes diverged from an unknown last common ancestor.

The remains of four Danuvius specimens were found at the Hammerschmiede site, including a nearly complete adult male with associated limb bones, finger bones, toe bones, and spine. The other Danuvius fossils belonged to two smaller adults and a juvenile. Böhme studied these fossils with the help of paleoanthropologist David Begun from the University of Toronto.

Danuvius is like an ape and a hominin in one,” wrote Böhme in an email to Gizmodo. “It was astonishing for us—and me—to realise how similar certain bones of Danuvius are to humans, as opposed to great apes.”

These animals were about as big as baboons, but with arms like bonobos and legs like hominins. They stood about 1 metre (3 feet) tall and weighed between 18 and 31 kilograms (40 – 68 pounds), which is very small compared to apes living today. With a broad, flat rib cage and a long lower back, these animals could maintain their centre of gravity while standing upright. Danuvius also had a strong opposable big toe, which it likely used to grasp branches.

Böhme said she was most surprised by similarities in the spine and legs bones of Danuvius compared to humans and other hominins and in contrast to other apes. This finding “was totally unexpected to all of us,” she said.

Bones from the hand of a male Danuvius. (Image: Christoph Jäckle)

To infer this animal’s posture and mode of locomotion, the researchers took their reconstructed version of Danuvius and performed some comparative anatomy. The “emerging picture of its locomotion is different from any known living creature,” Böhme told Gizmodo.

Danuvius moved through the trees by using both its extended hind limbs and its long arms for support and balance but not for pulling up its body, like other apes. The researchers aren’t sure how this method of moving through the trees conferred an advantage, but these early apes might have done it to get away from predators, such as big cats.

Böhme said the three main implications of her team’s new paper are that “upright walking originated in the trees” rather than on the ground and “our last common ancestor with apes did not go through a stage of hunched knuckle-walking.” Second, bipedal walking emerged during the Middle Miocene, which is 4 million to 6 million years earlier than previous estimates. And thirdly, this evolutionary process happened in Europe, not Africa.

This is an exciting new paper in that it proposes a potential evolutionary mode from which bipedalism emerged and then spread, but our relation to Danuvius and this species’ exact position within the larger primate family tree still needs to be determined. Importantly, Danuvius was a dryopith—an ancient group of European apes that some scientists, including Böhme, consider to be ancestral to African apes, though that remains a controversial opinion. Regardless, Böhme said Danuvius is now “the best model we have for the ‘missing link’ between humans and apes.”

More evidence to prove the bipedal nature of Danuvius would also be welcomed, Isaiah Nengo, an anthropologist at De Anza College, told Gizmodo.

“The inference for bipedalism, a large part of which is based on a tibia specimen that is rather crushed, is difficult to corroborate at this time,” said Nengo, who wasn’t involved with the new work. “The novel mode of locomotion proposal is a fascinating hypothesis, but the jury is out on the bipedalism claim until better materials are found.”

Indeed, it’s fascinating research, but more work still needs to be done to firmly place Danuvius in the larger evolutionary context and to better demonstrate its purported bipedal abilities. Still, the thought that two-legged walking may have emerged in the trees is truly astounding.