Scientists solve the mystery of the prehistoric ‘Burtele Foot’

By Will Dunham

WASHINGTON (Reuters) – Scientists have solved the mystery of 3.4 million-year-old fossils called “Burtele’s foot” discovered in Ethiopia in 2009, discovering that they belonged to an enigmatic human ancestor who lived alongside another closely related species during a poorly understood era of human evolution.

Based on the recent discovery nearby of 25 teeth and the jaw of a 4 1/2-year-old child, scientists determined that the eight-foot bones represent the species Australopithecus deyiremeda, which “combined ape-like and human-like traits and was first identified just a decade ago.”

The Burtele foot, so named because the bones were found at a site called Burtele in the Afar region of northeastern Ethiopia, showed that this species was “bipedal but still had an opposable big toe, a useful feature for climbing trees – evidence that although it walked upright, it did so in a different way than people do today.”

Fossils show that two closely related hominids – species in the human evolutionary lineage – lived at the same time and place, with Australopithecus afarensis being the other species. This raises the question of whether these close cousins ​​exploited the same resources or were different enough to avoid direct competition.

Australopithecus afarensis is the species that includes the famous Lucy fossil, discovered in 1974 in the Afar region.

The new findings add depth to the understanding of this period of human evolution, long before the appearance of our species, Homo sapiens, around 300,000 years ago.

“They provide us with the most conclusive evidence that Australopithecus afarensis – Lucy’s species – was not the only human ancestor that lived between 3.5 and 3.3 million years ago,” said paleoanthropologist Yohannes Haile-Selassie, director of the Institute of Human Origins at Arizona State University and lead author of the study published this week in the journal Nature.

“As a result, we now know that the early phases of our evolution were not linear, that is, only one species lived at any given time,” Haile-Selassie said.

Fossils showed that the two species walked differently and had different plant-based diets.

“Understanding the differences and similarities between these closely related hominids is essential to understanding their environments and perhaps even how interactions with each other, even indirectly, may have shaped their evolution and relationships with our own species,” said Naomi Levin, a University of Michigan geochemist and co-author of the study.

The big toe of Lucy’s species was non-opposable and more similar to ours. The big toe of Australopithecus deyiremeda was more of an ancestral form, similar to tree-climbing monkeys. On the ground, this species walked on two legs and probably grew not from its big toe, like Lucy’s species and modern humans, but from its second toe.

“It would certainly be less efficient to walk on two legs on the ground. However, it was more effective for climbing trees – not a bad trade-off, especially in areas where large predators are found,” Haile-Selassie said.

These included large saber-toothed cats and hyenas.

“We know that our lineage descends from an ancestor who had an opposable big toe,” Haile-Selassie said. “Human bipedalism must have undergone many experiments and modifications, with certain aspects of the foot, legs and pelvis evolving at different times.”

Chemical analysis of enamel samples from eight teeth of Australopithecus deyiremeda revealed the type of plants consumed by this species.

Lucy’s species was more of a generalist with a broader diet including grass-based foods and foods from trees and shrubs such as leaves, fruits or nuts. Australopithecus deyiremeda, in contrast, was limited to a diet based solely on trees and shrubs, similar to that of more primitive hominids. ⁠And foot anatomy beneficial for climbing may explain this.

“These species moved in different ways. There were many ways to be human at that time, and each way probably had an advantage. To me, it’s exciting that we can now associate these different ways of moving on two feet with different diets. We can link different morphological adaptations to different behaviors,” Levin said.

Eating a wider variety of foods could have given Australopithecus afarensis a competitive advantage.

“But we also have to ask,” Levin said, “whether it was Australopithecus deyiremeda that had the advantage, forcing Australopithecus afarensis to broaden its feeding strategy. Now that we know they ate different things and moved in different ways, we are that much closer to solving this coexistence puzzle.”

(Reporting by Will Dunham; editing by Daniel Wallis)