In nature, humans and apes have shown a variety of ways to move, from walking on two legs to climbing trees to walking on all fours. For scientists, the origins of human bipedal posture and movement have always been a mystery. Although past studies and the fossil record have attempted to shed light on this process, they have never been able to produce a clear historical picture. However, a recent study sheds light on the mystery. The study, which focuses on the skull of the 6 million-year-old ape fossil "lufengpithecus", provides us with important clues to the origin of bipedal movement. This is all thanks to a new approach: the analysis of the bony inner ear area using 3D CT scanning. The mysterious structure of the semicircular canal, located in the skull between our brain and our external ear, plays a vital role in providing a sense of balance and position. Zhang Yinan, a PhD student at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences and lead author of the **, explained: "The size and shape of semicircular canals are closely related to the way mammals, including apes and humans, move through the environment. With modern imaging techniques, we can delve into the internal structure of fossils and explore the anatomical details of semicircular canals, revealing how extinct mammals moved. "This study, published in the journal Innovation, provides a new perspective on how humans and apes move. This not only reveals the mysteries of biological evolution, but also gives us a deeper understanding of its origins. 
Our study points to a three-step evolution of human bipeds," added Terry Harrison, an anthropologist at New York University and one of the co-authors of the event. "First of all, the earliest apes' style of locomotion in trees is most similar to that of today's Asian gibbons. Second, the last common ancestor of apes and humans is similar to Lufeng wart in the athletic repertoire, using a combination of climbing and climbing, forelimb suspension, arboreal bipeds, and terrestrial tetrapods. It was from this extensive repertoire of ancestral sports that human bipeds evolved.
Most research on the evolution of ape locomotion has focused on comparing the bones of the limbs, shoulders, pelvis, and spine, and how they relate to different types of locomotor behaviors in living apes and humans. However, the diversity of extant ape-locomotor behavior and the incompleteness of the fossil record have hindered the development of a clear picture of the origin of human bipeds.
The discovery of the skull of Lu Fengweng, in China's Yunnan province in the early 1980s, gave scientists the opportunity to solve unanswered questions about the evolution of locomotion in new ways. However, severe compression and twisting of the skull obscured the bony ear region and led to what previous researchers thought was a fragile semicircular canal that had not been preserved.
To better explore the area, Zhang, Ni, and Harrison, along with IVPP and other researchers from the Yunnan Provincial Institute of Cultural Relics and Archaeology (YICRA), used 3D scanning technology to illuminate these parts of the skull to create a virtual reconstruction of the inner ear bone canal. They then compared these scans with those collected from other living and fossil apes in Asia, Europe, and Africa, as well as humans.
Our analysis shows that early great apes shared a locomotor ability, which is the ancestor of human bipeds," explained IVPP professor Xijun Ni, who led the project. "It appears that the inner ear provides a unique record of the evolutionary history of ape loctility, providing a valuable alternative to the study of the postcranial skeleton.
Most of the ape fossils and their inferred ancestors are somewhere between the gibbon and the African ape in terms of movement patterns," Ni added. "Later, with the acquisition of bipeds, the human lineage diverged from the great apes, as seen by the early human relatives Australopithecus from Africa.
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By studying the rate of evolutionary change of the bone maze, the international team proposed that climate change could be an important environmental catalyst for the diversification of ape and human movements.
"Lower global temperatures, associated with the accumulation of glacier ice sheets in the Northern Hemisphere about 3.2 million years ago, correspond to an increase in the rate of change of the bone maze, which may indicate a rapid acceleration in the evolutionary rate of ape and human movement," Harrison explained.
Reference: "Lufengpithecus Inner Ear Provides Evidence of a Common Locomotor Recurtore Ancestral to Human Bipedalism" by Yinan Zhang, Xijun Ni, Qiang Li, Thomas Stidham, Dan Lu, Feng Gao, Chi Zhang and Terry Harrison, February 14, 2024, The Innovation.
doi： 10.1016/j.xinn.2024.100580
Compiled from: scitechdaily