Scientists uncover the mystery of the ancient 'Burtele Foot'

WASHINGTON Researchers have finally unraveled the mystery surrounding the 3.4-million-year-old fossils known as the "Burtele Foot," unearthed in Ethiopia in 2009. The bones have now been identified as belonging to a previously enigmatic human ancestor that coexisted with a closely related species during a scarcely documented period of early human evolution.

Recent discoveries in the vicinity, including 25 teeth and a jawbone from a 4-and-a-half-year-old child, allowed scientists to determine that the eight foot bones belong to Australopithecus deyiremeda. This species, first described about a decade ago, exhibited a mix of ape-like and human-like traits.

The fossils from Burtele, in northeastern Ethiopias Afar region, show that Australopithecus deyiremeda was bipedal but retained an opposable big toe, suggesting adaptations for climbing trees. While the species walked upright, its gait differed significantly from that of modern humans.

These findings reveal that two closely related hominins shared the same habitat, with Australopithecus afarensisthe species of the famous fossil Lucybeing the other. This raises questions about whether the two species competed for the same resources or occupied distinct ecological niches.

"This evidence clearly shows that Lucys species was not the only human ancestor living between 3.5 and 3.3 million years ago," said paleoanthropologist Yohannes Haile-Selassie, director of Arizona State University's Institute of Human Origins and lead author of the study published in Nature. "It demonstrates that early human evolution was not a straight line with only one species at a time."

The analysis indicates that the two species had different walking styles and diets. "Studying the differences and similarities among these neighboring hominins is essential to understanding their environment and how their interactions, direct or indirect, may have influenced evolution," noted University of Michigan geochemist Naomi Levin, co-author of the study.

Unlike Lucys species, which had a non-opposable big toe similar to modern humans, Australopithecus deyiremeda retained a more primitive, tree-adapted toe. On the ground, it likely walked upright but pushed off using the second toe rather than the big toe, trading some walking efficiency for superior climbing abilitya useful adaptation in areas inhabited by predators like saber-toothed cats and hyenas.

"Our lineage descends from an ancestor with an opposable big toe," Haile-Selassie said. "Human bipedalism evolved through various experiments, with the foot, legs, and pelvis adapting at different times."

Chemical analysis of enamel from eight Australopithecus deyiremeda teeth revealed a diet limited to leaves, fruits, and nuts from trees and shrubs. In contrast, Australopithecus afarensis had a broader diet, including grass-based foods and other vegetation.

"These hominins moved and fed differently, showing that there were multiple successful ways to be human at this time," Levin explained. "Linking foot anatomy and locomotion to dietary habits helps us understand their behavior and coexistence."

The study suggests that dietary differences may have reduced direct competition between species, offering new insights into how early human ancestors shared ecosystems.

Analysis: A Complex Web of Early Human Evolution

The recent discovery of the "Burtele Foot" fossils sheds light on the nuanced and diverse nature of early human evolution. These findings, now attributed to Australopithecus deyiremeda, reveal that multiple hominin species coexisted in the same region at the same time, each with distinct traits and behaviors that shaped their survival strategies. Unlike Lucy's species, which was more adapted for ground locomotion, Australopithecus deyiremeda retained an opposable big toe, suggesting that climbing trees was still an essential part of its lifestyle. This adaptation likely offered crucial advantages in environments populated by predators, such as saber-toothed cats.

The evidence indicates that these hominins did not simply compete for the same resources but likely occupied different ecological niches. While both species were bipedal, their walking patterns and dietary preferences differed. Australopithecus deyiremeda had a more limited diet focused on tree-based foods, whereas Australopithecus afarensis had a broader range of food sources, including grass-based vegetation. This dietary divergence may have alleviated direct competition between the two species, providing each with a more sustainable way to thrive in a shared ecosystem.

These findings challenge the long-held assumption that early human evolution followed a linear path with one species dominating at a time. Instead, it presents a more intricate picture of cohabitation and adaptation. By studying the subtle differences between neighboring hominins, scientists can better understand the environmental pressures and behaviors that shaped human evolution. Early human ancestors, it seems, were far more flexible in their survival strategies than previously thought.

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• Scientists solve the mystery of the prehistoric 'Burtele Foot'