A New Chapter in Human Ancestor Discovery: The Bipedal Tree-Climber
The University of Barcelona
In 2009, an extraordinary find was made at the Woranso-Mille site in Ethiopia's central Afar region. A team led by paleoanthropologist Yohannes Haile-Selassie from Arizona State University unearthed eight bones from the foot of a human ancestor, known as the Burtele Foot. This discovery, however, presented a unique challenge: the fossils did not belong to any known human ancestor species from Africa. Fast forward to the present, and a groundbreaking study published in the journal Nature reveals the true identity of the Burtele Foot.
The study, led by Haile-Selassie, uncovers a fascinating story. The Burtele Foot, dating back approximately 3.4 million years, belongs to the species Australopithecus deyiremeda, a hominid fossil first discovered at the Woranso-Mille site in 2015. This finding is significant because it demonstrates that A. deyiremeda was a bipedal species, capable of walking on two limbs, and also had a prehensile big toe, similar to that of chimpanzees, indicating a unique ability to live in trees.
The international team of experts, including Professor Lluís Gibert from the University of Barcelona, played a crucial role in this discovery. Geological analyses were instrumental in dating the fossils and linking them to A. deyiremeda. This meticulous work provided the missing piece in the puzzle of human evolution.
A Fossilized Foot with a Unique Story
The Burtele Foot offers a unique perspective on human evolution. It challenges the long-standing debate surrounding the coexistence of Australopithecus afarensis, famously known as Lucy, discovered in Ethiopia in 1974. The Woranso-Mille site is now recognized as a pivotal location, as it provides evidence of two related hominid species living in the same area at the same time.
Yohannes Haile-Selassie, director of the Institute of Human Origins and professor at the School of Human Evolution and Social Change, emphasizes the significance of this discovery. He notes that the Burtele Foot is distinct from Lucy's species, Australopithecus afarensis, which was well-documented at that time.
Bipedalism's Complex Evolution
The Burtele Foot reveals a more primitive form of bipedalism compared to Lucy's species. It retained an opposable big toe, crucial for climbing, and had longer, more flexible toes, suitable for grasping. However, a fascinating detail emerges: when A. deyiremeda walked on two limbs, it likely pushed off with the second toe, unlike modern humans who use the big toe for this purpose.
Haile-Selassie highlights the rarity of naming a species based on postcranial elements, which include bones below the neck. Typically, jaws and teeth are used for species recognition. The discovery of the Burtele Foot is even more remarkable when compared to the Ardipithecus ramidus fossil, an early hominid ancestor with an opposable big toe, dating back 4.4 million years.
This finding underscores the diverse forms of bipedality in early human ancestors. It suggests that there were multiple ways of walking on two legs, challenging the notion of a single, universal method. The Burtele Foot discovery is a testament to the complexity and diversity of human evolution, inviting further exploration and discussion.
