A groundbreaking discovery of a 7.2-million-year-old femur at the Azmaka fossil site in southern Bulgaria reveals a unique blend of locomotor features, suggesting both quadrupedal and bipedal abilities. This significant finding involves a research team led by Professor Madeleine Böhme from the Senckenberg Center for Human Evolution and Paleoenvironment at the University of Tübingen. The fossil has been tentatively linked to Grecopithecus, a fossilized species of ape known from fragmented archaeological sites in the Balkans, which is considered by some as a contender for the earliest known human species.
Grecopithecus freibergii inhabited the dusty savanna of the Athens Basin 7.2 million years ago. This image from Pyrgos Vasilisis, the site of discovery, shows a southeastern view over Athens’ plains, beneath reddish clouds of Saharan dust. Background features include Mount Himethos and Mount Lycabettos. Image credit: Velizar Simeonovski.
Researchers regard Grecopithecus as a controversial late Miocene ape fossil, estimated to be around 7.2 million years old.
Some experts speculate that this ancient species could represent the earliest humans, potentially predating fossils traditionally linked to early human ancestry in Africa.
The fossil record of Grecopithecus includes a partial lower jaw discovered near Athens, Greece, in 1944, alongside isolated upper premolar fossils from Bulgaria examined in the 2010s.
“This ancestor from 7.2 million years ago is classified within the genus Grecopithecus and may represent the oldest known hominid,” stated David Bigan, a professor at the University of Toronto and co-author of the study.
The analysis in the study involved nearly complete femurs from Grecopithecus unearthed from the Azmaka site.
The newly discovered fossil, located in floodplain sediments dating back approximately 7.2 million years, showcases distinctive features. The Azmaka femur’s bulbous head is noticeably separated from the neck, with an elongated, diagonally ascending medial edge characteristic of hominids.
While this find does not fully represent the range of adaptations seen in later bipedal species, the angle of the neck axis falls within the lower spectrum observed in modern humans and approaches estimates for early human ancestors such as Orrorin, but remains below the typical angle found in suspensory apes like orangutans.
Researchers suggest that this combination of anatomical features indicates a transitional form of bipedalism that is neither specialized for climbing nor fully adapted for terrestrial life.
Weight estimates based on the dimensions of the femur suggest Grecopithecus weighed approximately 23-24 kg, akin to a small chimpanzee.
Professor Nikolai Spasov of the Bulgarian National Museum of Natural History remarked, “Numerous external and internal morphological traits, such as the elongated neck between the femoral shaft and head, the specific attachment points for the gluteal muscles, and the robust nature of the external bone layer, share similarities with our bipedal hominin ancestors and modern humans.”
“These anatomical features differ significantly from those of tree-dwelling apes,” he added. “Nevertheless, Grecopithecus did not walk in the same manner as modern humans.”
The environmental context of the Azmaka site indicates a scrub and forest savannah near a braided river system, suggesting that early terrestrial bipeds may have evolved outside of jungle habitats.
The authors hypothesize that the descendants of this group might have migrated from Eurasia to Africa during the late Miocene in response to climatic and environmental changes in the eastern Mediterranean, potentially influencing the ancestry of later African apes and hominids.
Whether the Azmaka femur ultimately reconstructs the geographic story of human origins remains contingent upon future discoveries.
Yet currently, it provides a rare insight into the origins of upright walking within a landscape characterized by seasonal rivers and open forests, millions of years prior to the emergence of the first widely recognized human ancestors in Africa.
Grecopithecus exemplifies a pivotal moment in human evolution, representing the transition from arboreal to terrestrial ancestors, akin to those from approximately 12 million years ago, including Danuvius guggenmosi, discovered at the Hammerschmiede site in southern Germany and more recently in East Africa,” emphasized Professor Bigan.
“In essence, you could classify this as a missing link. Grecopithecus is likely a descendant of apes from the Balkans and Anatolia that existed 8 to 9 million years ago, including Ouranopithecus and Anadrovicius, evolving from Western and Central European ancestors.
“Significant climate fluctuations in the eastern Mediterranean and Western Asia resulted in the periodic formation of extensive semi-desert landscapes between 8 and 6 million years ago,” he concluded. “This prompted a dispersal of Eurasian mammals into Africa, laying the groundwork for the contemporary savannah mammal fauna.”
The team’s findings were published in the November 2025 issue of Paleobiodiversity and Paleoenvironment.
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N. Spasov et al. Early forms of bipedal locomotion in terrestrial humans during the Late Miocene of Bulgaria. Paleobio Paleoembu, published online on November 13, 2025. doi: 10.1007/s12549-025-00691-0
Source: www.sci.news
