An ancestor's ancestor
In an old iron ore mine near the town of Rudabánya, paleontologists unearthed fossil fragments that challenge ideas about how humans came to walk on two legs. The fragments form a partial pelvis from Rudapithecus hungaricus, an ape that lived here approximately 10 million years ago. This region in the Late Miocene was a subtropical swamp forest on the shores of the Pannonian Sea, a shallow inland sea that has long since disappeared. The discovery of this pelvis is important because this part of the skeleton is rarely preserved and shows direct evidence about an animal's posture and movement.
Analysis of the Rudapithecus pelvis, led by researcher Carol Ward, shows a creature with a unique blend of anatomical features. While it likely moved through trees like modern apes, holding its body upright, its lower back was surprisingly flexible. This flexibility is a trait shared with humans, allowing us to stand and walk efficiently on two legs, and is different from the long pelvis and short, stiff lower back of modern African apes like chimpanzees and gorillas. The discovery suggests that the common ancestor of African apes and humans might not have been built like today's apes. Instead, it may have possessed a more flexible torso, meaning our own lineage may never have passed through a knuckle-walking phase.
A flexible build
The shape of the Rudapithecus hipbone provides specific clues to its upright, or orthograde, posture. The iliac blades, the large, flat upper parts of the pelvis, are broad and oriented in a way similar to all modern apes, indicating a stable torso. However, unlike modern great apes, the lower part of the ilium is not elongated. This elongation in chimpanzees and gorillas is associated with a stiffened, shorter lower back, an adaptation for their large size and knuckle-walking locomotion.
The Rudapithecus pelvis, by contrast, points to a longer and more mobile lumbar spine. This animal was relatively small, about the size of a medium dog, which would have accommodated a more flexible torso. This flexibility would have allowed it to stand upright when on the ground with greater ease than a chimpanzee. Researchers used 3D modeling to complete the shape of the fragmented fossil, comparing the digital model to modern animals to understand its function. The finding shows that a body plan suited for upright posture existed in European apes millions of years before the first bipedal hominins appeared in Africa.