A single right thighbone, nicknamed “Diva” and buried in Bulgaria for 7.2 million years, may push the origin of upright walking out of Africa and into Europe.
Researchers excavating at Azmaka, near Chirpan in southern Bulgaria, found the femur in 2016. It measures 21.5 centimetres long and is nearly complete. According to the announcement, it predates every known hominin fossil, including all those from Africa.
The team, led by Madelaine Böhme at the University of Tübingen, has been working the site since 2008. The bone was recovered from river-deposited sediments roughly 20 metres thick, in sands independently dated to 7.2 million years old.
What the bone shows
Böhme’s team CT-scanned and measured the femur in detail. They identified a long, straight femoral neck — a feature seen in bipedal hominins but not in knuckle-walking apes — capable of bearing a vertical load. The outer bone layer is thicker on the bottom of the neck than the top, consistent with weight-bearing. A ridge on the back of the bone marks where gluteal muscles attached. “They are important because they hold the back upright,” says Böhme.
The only ape species identified at Azmaka is Graecopithecus freybergi, known elsewhere only from a damaged jawbone found in Greece, a tooth from North Macedonia, and a single tooth from the same site. The team attributes the femur to that species by default. “It’s the most parsimonious choice we can do for now,” says Clément Zanolli at the University of Bordeaux.
Significant pushback
Zanolli describes the femur as “quite well preserved,” calling it “really, really rare in the Miocene fossil record for hominids.” But he stops short of endorsing the bipedality claim. “Some are biped-like, but others are quadruped-like. So, it’s quite difficult to know exactly what was the locomotor behaviour.”
Kelsey Pugh at OCAD University in Toronto points out that the link between the femur and Graecopithecus is loose, and that the field has been steadily revising which skeletal features can reliably signal upright walking. Many traits once considered unique to bipedal hominins have since been found in quadrupedal apes. “We’re raising the standard of what is required,” she says. The femur alone does not meet it.
The debate sits alongside an unresolved dispute over Sahelanthropus tchadensis, from Chad, the species most widely accepted as the earliest hominin. It lived around 7 million years ago — slightly more recently than the Azmaka specimen — and its own locomotion remains contested. The European find adds a new front to a broader argument about where and how bipedality first appeared.
Photo by Pixabay
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