The inner ear of a 6-million-year-old fossil monkey sheds light on the development of human mobility. Humans and our closest living relatives, the great apes, display an extraordinary diversity of locomotion, from walking on two legs to climbing trees and walking on all fours on all fours.

Although scientists have long been interested in how human bipedal posture and locomotion evolved from a quadrupedal ancestor, neither past research nor the fossil record has allowed us to reconstruct a clear and definitive history of the early evolutionary stages that led to human bipedalism.

But a new study focused on recently discovered evidence from the skulls of the fossil monkey Lufengpithecus. This 6-million-year-old fossil offers important clues about the origin of bipedalism through a new method: analysis of the bony inner ear region using 3D CT.

“The semicircular canals located in the skull between our brain and the outer ear are critical to our sense of balance and position when we move, and they provide a key component of our locomotion that most people are probably unaware of,” explains Yinan. Zhang is a doctoral student at the Institute of Vertebrate Paleontology and Paleoanthropology at the Chinese Academy of Sciences (IVPP) and lead author of the paper published in the journal Innovation.

“The size and shape of the semicircular canals are related to how mammals, including great apes and humans, moved around their environments. Using modern imaging techniques, we were able to visualize the internal structure of fossil skulls and anatomical details of the semicircular canals to reveal how extinct mammals moved.” “We were able to examine it.”

Evolutionary steps towards bipedalism

“Our study points to a three-stage evolution of human bipedalism,” adds Terry Harrison, an anthropologist at New York University and a co-author of the paper. “First, the first great apes moved around trees in a way that most closely resembles what Asian gibbons do today. Second, the last common ancestor of great apes and humans looked like this: lufengpithecus In its locomotor repertoire, it uses a combination of crawling and climbing, suspension of the forelimbs, arboreal bipedalism, and terrestrial quadrupedalism. “Human bipedalism evolved from this broad locomotor repertoire of its ancestors.”

Most studies on the evolution of locomotion in great apes have focused on comparing the bones of the limbs, shoulders, pelvis, and spine and how they relate to the different types of locomotion seen in living apes and humans. But the diversity of locomotor behavior in living great apes and the lack of a fossil record have prevented a clear picture of the origin of human bipedalism from emerging.

Technological developments in mineral exploration

Skull lufengpithekaFirst discovered in China’s Yunnan province in the early 1980s, the discovery gave scientists new ways to answer unanswered questions about the evolution of locomotion. However, severe compression and distortion of the skulls obscured the bony area of ​​the ear, leading earlier researchers to believe that the sensitive semicircular canals were not preserved.

To better investigate this area, Zhang, Nie, and Harrison, along with other researchers from IVPP and the Yunnan Institute of Cultural Relics and Archeology (YICRA), used 3D scanning technology to illuminate these parts of the skull to create a virtual reconstruction. Bone canals of the inner ear. They then compared these scans to other living and fossil monkeys and humans from Asia, Europe and Africa.

“Our analysis shows that the first great apes had a locomotor repertoire that was ancestral to human bipedalism,” explains IVPP Professor Sijun Ni, who led the project. “The inner ear appears to be a unique record of the evolutionary history of ape locomotion and offers an invaluable alternative for studying the postcranial skeleton.”

“Most fossil monkeys and their putative ancestors lie in the middle of the movement between gibbons and African monkeys,” Ni adds. “Later, the human race diverged from the great apes with the acquisition of bipedalism. Australopithecus, “Early relative of man from Africa”.

An international team studying the pace of evolutionary change in the bone labyrinth has suggested that climate change may have been an important ecological catalyst promoting the diversification of the locomotion system of great apes and humans.

“Colder global temperatures associated with the formation of ice sheets in the Northern Hemisphere approximately 3.2 million years ago are consistent with increased rates of change in the bony labyrinth and may indicate a rapid increase in the rates of monkey and human musculoskeletal evolution,” explains Harrison.