Discoveries indicate that 7.2 million years ago, early apes might have been walking upright in present-day Bulgaria. Researchers uncovered ancient leg bones exhibiting characteristics of bipedalism.

These leg bones predate all known human fossils, including those from Africa, suggesting that bipedalism—a critical milestone in human evolution—may have originated in Europe rather than Africa.

“The earliest signs of bipedalism are found in Europe,” states Madeleine Boehme, from the University of Tübingen, Germany.

Boehme and a dedicated team have been excavating at Azmaka near Chirpan, Bulgaria, since 2008, uncovering a sediment layer approximately 20 meters thick, deposited by rivers over time.

A crucial find in 2016 was a right femur, known to be 7.2 million years old and nearly intact, nicknamed “Diva.” This femur, measuring 21.5 centimeters, offers substantial insight into the locomotion of early humans.

“This discovery is incredibly significant,” remarks Clement Zanoli from the University of Bordeaux, France, who was not involved in the study. “The femur’s exceptional preservation is rare in the Miocene hominin fossil record.”

During early epochs, Europe hosted various great apes, yet by 7.2 million years ago, most had become extinct. Today, all closest relatives to modern apes are located in Africa, as are the earliest human ancestors, or hominins.

The only ape confirmed from Azmaka is Grecopithecus freybegii, known primarily from a damaged jawbone found in Greece, and some teeth from North Macedonia and Azmaka. Consequently, Böhme’s team posits that the femur likely belongs to Grecopithecus.

“This is the most reasonable assumption at this time,” states Zanoli, but he stresses that more fossil evidence is necessary for stronger validation.

“The relationships among these fossils remain unclear,” explains Kelsey Pugh from OCAD University, Toronto, Canada.

Böhme’s team meticulously measured the femur and conducted CT scans, uncovering attributes indicative of a bipedal organism. Notably, a short neck that laterally extends and forms a rounded ball fits into the pelvis, resembling structures found in bipedal hominids but absent in knuckle-walking species. Additionally, the outer bone layer’s thickness at the neck’s base supports vertical loads.

An additional ridge was identified, which would have allowed for the attachment of buttock muscles, playing a vital role in maintaining an upright posture, according to Boehme.

While other scientists find the findings intriguing, they remain unconvinced. “This femur displays several traits,” Zanoli points out. “Some suggest bipedalism, while others imply quadrupedal movement. Hence, determining the locomotion remains complex.”

The nuanced study of extinct great apes has revealed increasing challenges in accurately diagnosing bipedalism based solely on isolated fossil bones. Pugh notes, “Many features once thought exclusive to bipedal hominids have also been noted in quadrupedal apes. Thus, prioritization of diagnostic traits is crucial.”

Much attention has focused on Sahelanthropus tchadensis, known from a solitary location in Chad and considered the earliest hominid. This species lived 7 million years ago, slightly younger than the Azmaka specimen. The femur of Sahelanthropus has long fueled debate about bipedalism.

Boehme and her team are determined to establish that significant steps in early human evolution transpired in Europe. They’ve identified potential hominid features in Grecopithecus, despite past controversies linked to a damaged jawbone. Furthermore, they have also detailed another European ape, Danuvius guggenmosi, which existed approximately 11.6 million years ago.

These early human-like ancestors might have migrated to Africa, potentially driven by climate changes. Research indicates that this migration likely gave rise to all subsequent hominins, including modern humans.

Zanoli comments, “Numerous other animals migrated between Africa and Eurasia. If fauna can do it, why can’t hominins?”

Yet, Professor Pugh asserts that further discoveries are essential to substantiate bipedalism evidence in Grecopithecus, allowing detailed analysis of relationships among other apes and early humans. Without this, she emphasizes that it’s premature to construct comprehensive evolutionary narratives.

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