Fossils suggest tree-dwelling apes walked upright long before hominids did

Tree-dwelling apes in Europe strode upright around 5 million years before members of the human evolutionary family hit the ground walking in Africa.

That’s the implication of fossils from a previously unknown ape that lived in what’s now Germany about 11.6 million years ago, say paleontologist Madelaine Böhme of the University of Tübingen in Germany and her colleagues. But the relation, if any, of these finds to the evolution of a two-legged stride in hominids by perhaps 6 million years ago is hazy (SN: 9/11/04).

Excavations in a section of a Bavarian clay pit produced 37 fossils from the ancient ape, dubbed Danuvius guggenmosi by the investigators. Bones from the most complete of four individuals represented by the new finds cover about 15 percent of that creature’s skeleton, including nearly complete specimens from the forearm and lower leg, Böhme’s team reports online November 6 in Nature. Earlier research had generated age estimates for fossil-bearing sediment in the German pit.

Danuvius’ limbs, spine and body proportions indicate that it could hang from branches, like present-day orangutans and gibbons, as well as walk on two legs slowly, somewhat like hominids that originated in Africa roughly 6 million to 7 million years ago, the researchers say. No other fossil or living ape has moved in trees and on the ground precisely as Danuvius did, they conclude. An ape built like Danuvius likely served as a common ancestor of great apes and hominids that emerged roughly 7 million years ago or more, Böhme contends.

If true, Danuvius’ body design would upend the long-standing idea that hominids evolved an upright stance after splitting from a common knuckle-walking, chimplike ancestor in Africa. The new finds also challenge an argument that hominids evolved from ancient apes built much like modern orangutans, which walk upright on tree branches while grasping other branches for support (SN: 7/30/07).

A Danuvius link to hominids would fit with evidence that a 4.4-million-year-old hominid called Ardipithecus ramidus combined an upright gait with adept tree climbing (SN: 4/2/18). But A. ramidus weighed about three times as much as Danuvius, which ranged from an estimated 17 to 31 kilograms, Böhme’s team says. Based on available fossils, the considerably smaller and older Danuvius was designed for less efficient walking and better climbing than A. ramidus was, says paleoanthropologist Scott Williams of New York University who was not involved in the new study.

Despite those differences, “upright walking preceded the great ape/human split and likely started in Europe,” Böhme says.

Many fossil apes dating to between 13 million and 5.3 million years ago have been found in Europe (SN: 5/22/17) and, to a lesser extent, Africa (SN: 8/9/17). Those finds, however, included no completely intact limb bones.

Measurements of three Danuvius limb bones, two of which come from the same adult male, indicate that this extinct ape relied equally on its forelimbs and hind limbs. Comparisons of two Danuvius spinal bones with those of fossil and living apes suggest that the newly discovered animal had a relatively long, inwardly curving back capable of supporting an upright stance. Grasping, opposable big toes helped to stabilize flat feet while walking, the researchers say, while curved fingers, much like those of present-day chimps and other apes, would have aided climbing and maneuvering in trees.

Danuvius’ big toes were long and strong enough to grip thin branches and hanging vines in trees, Böhme says. As a result, Danuvius could have held itself in place in a thicket of branches or vines to hide from large, predatory cats, she speculates.

If further fossil finds confirm that Danuvius and perhaps other ancient tree-dwelling apes stood upright, “it would show that our [human] lineage never did go through a hunched-over stage of walking because we were always upright,” says paleoanthropologist Jeremy DeSilva of Dartmouth College.

It’s possible, though, that Danuvius independently evolved a form of upright walking on tree branches that had nothing to do with the appearance of a two-legged gait in hominids, says DeSilva, who was not a member of Böhme’s team.

The latter possibility appears most likely, Williams says. Danuvius shares enough of its known anatomy with modern African and Asian monkeys, gibbons as well as other fossil apes for scientists to question whether the German creature had any direct influence on hominids’ upright stance, he says.

Still, the discovery of Danuvius “adds an exciting piece to the puzzle” of ancient ape evolution, Williams says.