Mysterious Ancient Ape May Have Evolved a Key Human Trait

Around 7 million years ago, a little creature braved wildcats and hyenas to cross the floodplains of Bulgaria – and she may have done so on two legs.

A recently described fossil femur offers evidence that this extinct ape, estimated to have weighed around 24 kilograms (53 pounds) and tentatively identified as Graecopithecus freybergi, displayed multiple anatomical features consistent with bipedalism.

In a press statement, the researchers who analyzed the ancient thighbone posit that this compact creature may have therefore been our premier predecessor – but the claim is not without controversy.

"At 7.2 million years old, this ancestor, which we classify as belonging to the genus Graecopithecus, could be the oldest known human," says David Begun, a paleoanthropologist at the University of Toronto and study co-author.

Graecopithecus' lineage has been a contentious hypothesis for years. Other scientists refute the researchers' conclusion, including the implication that humanity emerged in the Balkans rather than Africa, for various reasons, including a dearth of evidence.

Previously, Graecopithecus was only known from two fossils: a lower jawbone found in Greece in 1944 and a premolar tooth found in Bulgaria in 2012. The latter was unearthed at the Azmaka excavation site, the same place where the previously mentioned fossil femur was found in 2016.

In this most recent study, the researchers characterize the owner of the ancient thighbone as a small-chimpanzee-sized adult female. For comparison, her femur was similar in size to that of the meat-eating mammals that prowled the plains, including giant otters, early hyenas, and proto-badgers.

A comparison of the fossil femur found at Azmaka, Bulgaria, pictured left, the femur from the famous Lucy fossil (Australopithecus afarensis), center, and a femur from a chimpanzee. The femoral neck region is highlighted in red, showing a longer length and a more upward orientation in Graecopithecus and Australopithecus. (Spassov et al., Palaeobio. Palaeoenv., 2026)

Yet the femur's morphology is more telling than its size. For example, it displays a relatively long femoral neck, which connects the shaft of the thighbone to the femoral head, which then slots into the hip. A longer femoral neck suggests bipedalism because it allows the leg to move more freely.

It also represents the evolutionary trade-off between strength and mobility. As humans became more modern, we gained a greater range of motion at the expense of stability and climbing power.

The researchers also cite the insertion points for the gluteus muscles, which appear to be conducive to bipedalism. Additionally, the thickness of the bone's outer layer is indicative of the stresses caused by upright locomotion.

Yet the fossil also shows features common to quadrupedal creatures. In the paper, the researchers say the femur represents a "transitional position between African great apes and habitual bipedal hominins."

The Azmaka region during the late Miocene would have been a sparsely forested savannah, supporting the idea that bipedalism may have emerged as woody landscapes turned to grasslands.

But despite potentially ditching the trees, this ape would not have walked exactly as we do. Her femoral features suggest facultative bipedal locomotor skills, meaning she may have been able to walk upright when advantageous, but also moved along the ground using all four limbs.

Perhaps she assumed an upright posture to scan for predators, forage more effectively in ever-sparser environs, or carry her offspring between arboreal nesting sites.

Given the environmental and climatic shifts of the time, it's possible that Graecopithecus also traveled from the Balkans to Africa, the researchers hypothesize.

"We know that large-scale climate changes in the eastern Mediterranean and western Asia led to the periodic emergence of extensive semi-deserts and deserts 8 to 6 million years ago," says Madelaine Böhme, a paleontologist at the University of Tübingen and study co-author.

"This set off several waves of dispersal of Eurasian mammals to Africa and laid the foundation for today's mammal fauna of African savannas."

Various views of the femur discovered at the Azmaka excavation site in Bulgaria. Images f and g show muscular attachment sites. Images h through k include, in ordered, scans of the FM3549AZM6 femur, that of a Homo sapiens from a modern Roman burial, the small old world monkey Mesopithecus, and a chimpanzee. (Spassov et al., Palaeobio. Palaeoenv., 2026)

However, last time Begun and Böhme made this claim, other experts raised their eyebrows.

"A hominin or even a hominine (modern African ape) ancestor located in a fairly isolated place in southern Europe doesn't make much sense geographically as the ancestor of modern African apes, or particular the oldest ancestor of African hominins," Rick Potts of the Smithsonian museum told The Washington Post in 2017.

Related: 'Lucy' Was Neighbors With an Even Older Human Ancestor, Fossils Reveal

Overall, this discovery is a reminder of the uncertainty, controversy, and potential mutability of our human origins. On any given day paleoanthropologists can unearth some curious fossil that ignites arguments about our ancestry.

This study was published in Paleobiodiversity & Paleoenvironments.