A recent investigation conducted by paleoanthropologists from the United States and Canada has focused on the morphology of the hominid talus, a significant bone in the ankle that connects to the tibia and calcaneus of the foot. Ardipithecus ramidus, a hominid species that existed in eastern Africa approximately 4.4 million years ago, was at the center of this study. The researchers discovered that the fossil exhibits similarities to the talus of chimpanzees and gorillas, which are adapted for vertical climbing and terrestrial quadrupedal locomotion—a form of movement where animals traverse on all fours with the entire sole of the foot touching the ground, including the heel. Additionally, the authors confirmed the presence of derived features in the specimen that align with earlier suggestions for improved extrusion mechanisms in the legs of Ardipithecus ramidus.
Ardipithecus ramidus, a hominid that existed in Africa over 4 million years ago. Illustration by Arturo Asensio, from Quo.es.
Partial skeleton from 4.4 million years ago, Ardipithecus ramidus, affectionately dubbed “Aldi,” was uncovered in 1994.
This species featured an ape-sized brain and had grasping big toes adapted for climbing trees.
It walked on two legs, and its upper canine teeth were diamond-shaped as opposed to the V-shape commonly found in chimpanzees.
“Aldi represents one of the oldest and most complete skeletons discovered,” remarked Dr. Thomas (Cody) Plan, a researcher at Washington University in St. Louis.
“Aldi is roughly a million years older than ‘Lucy’, another renowned early human ancestor, and signifies an early phase in human evolution.”
“Oneof the surprising aspects of this find was that, despite walking upright, Aldi retained many monkey-like characteristics, such as its grasping feet.”
“Great apes, including chimpanzees and gorillas, possess forked big toes that facilitate gripping tree branches while climbing.”
“However, it also exhibited traits consistent with our lineage. Ardipithecus truly represents a transitional species.”
Initially, scientists speculated that Ardi’s locomotion resembled a common form rather than being typical of African apes, leading them to conclude that this early human ancestor was not particularly ape-like, which startled the paleoanthropology community.
“From their analysis, they inferred that contemporary African apes, like chimpanzees and gorillas, represent a dead end, or a kind of evolutionary cul-de-sac. Dead end underscores the evolutionary process rather than the point at which humans emerged,” stated Dr. Puran.
“Instead, they posited that Ardi offered evidence of a more generalized ancestry that was less akin to chimpanzees and gorillas.”
By examining the ankles of chimpanzees and gorillas, researchers can gain insights into their movement, especially regarding their vertical tree climbing techniques.
This crucial bone also sheds light on how early species transitioned to bipedalism.
For the recent study, Dr. Plan and his team compared Ardi’s ankles to those of great apes, monkeys, and early humans.
Their findings indicated that Ardi’s ankle is the only one within the primate fossil record that shares similarities with African apes.
These apes are recognized for their adaptations to vertical climbing and terrestrial quadrupedal locomotion, suggesting that Ardi might have utilized their feet similarly.
Alongside these primitive traits, Ardi’s talus exhibited signs of an enhanced foot extrusion mechanism.
This complexity points to a blend of climbing and locomotor behaviors in this early human species, which is crucial in understanding the evolution of bipedalism.
“This discovery is both controversial and aligns with earlier theories,” Mr. Pran noted.
“While there is no disagreement regarding the significance of Aldi’s find, many in the field would argue that the initial interpretation was likely flawed.”
“Thus, this paper represents a reevaluation of the original views that distanced Aldi from chimpanzees and gorillas.”
“It’s vital to understand that our paper does not claim that humans evolved from chimpanzees.”
“However, this study further supports the hypothesis that the common ancestor of humans and chimpanzees was likely very similar to today’s chimpanzees.”
For more details, refer to the paper published in the journal Communication Biology.
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TC Plan et al. 2025. Ardipithecus ramidus Ankle provides evidence of African ape-like vertical climbing in early humans. Commun. Biol. August 1454. doi: 10.1038/s42003-025-08711-7
Source: www.sci.news
