Arizona State University Uncovers Coexisting Ancestors: The Burtele Foot and Australopithecus deyiremeda
For more than a decade the Science and Technology team at Arizona State University (ASU) has been digging deep into the Afar Rift in Ethiopia. The work culminated in the discovery of a single foot fossil, the Burtele Foot, that connects two early hominin species that once lived side‑by‑side. The research offers a clearer view of how ancient human ancestors moved, ate, and adapted in a changing environment—data that may help us understand how today’s species respond to climate shifts.
Why the Burtele Foot Matters
When the first fragments of the Burtele Foot were found in 2009, the team was excited but cautious. The toe was unusually long and had an opposable big toe—a trait that suggests a climbing ability still present in the earliest human ancestors. At the time, the foot could not be matched to any known species because the field still lacked the cranial, jaw and tooth material typically used in species identification. The site’s significance lies in its evidence of two distinct hominins co‑existing during the same geological period.
The Two Species: Australopithecus deyiremeda and Australopithecus afarensis
Arizona State University’s Professor Yohannes Haile‑Selassie first announced the presence of a new species, Australopithecus deyiremeda, in 2015 using skull and dental remains discovered at the same site. Ten years later, after a sustained effort and further discoveries, the Burtele Foot could be confidently assigned to this species. In contrast, Australopithecus afarensis, best known from the famous Lucy specimen, is differentiated by an adducted (non‑opposable) big toe and a different foot morphology.
Connecting Foot to Species: The Methodology
Determining the species affiliation of a postcranial element requires robust comparative data. The research team used a combination of anatomical comparison, micro‑CT scanning, and statistical analysis:
- Anatomical Comparison – The foot’s pedal morphology was compared to the foot bones of other known australopithecines.
- Micro‑CT Scanning – High‑resolution scans allowed researchers to reconstruct the foot’s 3D structure, revealing subtler traits such as the positioning of the metatarsals and the shape of the plantar surface.
- Statistical Analysis – By measuring the foot’s dimensions relative to known samples, scientists identified a pattern that best matched the new species.
With the foot placed within Australopithecus deyiremeda, ASU anthropologists could start to reconstruct the species’ locomotion habits in more detail.
Locomotion Insights: A More Primitive Biped?
The Burtele Foot differs greatly from the foot of Lucy’s species. While the modern human foot pushes off the second digit during bipedal walking, the Burtele Foot’s structure indicates that the foot likely used the big toe as a secondary lever during locomotion. The presence of an opposable big toe signifies that even a few hundred thousand years after Lucy’s appearance, a more primitive biped was still evolving. The fossil demonstrates the diversity of bipedal strategies and suggests that early hominins experimented with multiple ways of walking before the modern pattern emerged.
What Teeth Reveal About Diet and Ecology
Dietary reconstruction is essential for understanding ecological pressures driving evolution. Professors from Arizona State and the University of Michigan performed isotope analysis on eight of the 25 teeth recovered from the Burtele site. They measured the ratio of carbon isotopes (13C to 12C) to infer the types of plants the animals ate.
The results were clear: Australopithecus deyiremeda primarily consumed C3 plants—trees, shrubs, and some grasses—while avoiding the C4 grasses that Australopithecus afarensis exploited. This dietary divergence suggests that the two species carved different ecological niches: one remained hill‑lily shrub specialists, the other expanded into mixed forests and early grasslands.
Implications for Coexistence
By occupying separate dietary niches, A. deyiremeda and A. afarensis could coexist without direct competition. The careful partitioning of food sources and habitat preferences likely reduced interspecies conflict. Such findings provide a model to understand how multiple species can occupy the same geographic area when each adapts to distinct resources.
Growth Patterns from the Juvenile Mandible
Microscopic analysis of a juvenile mandible recovered from the same layer uncovered a full set of baby teeth and several adult teeth developing inside the jaw. Using pattern and rate of tooth development, scientists estimated the juvenile’s age to be about 4½ years at death.
Consistent with other australopithecines, the development sequence showed a disconnect between the front teeth (incisors) and the back chewing teeth (molars). These patterns mirror growth cycles seen in living non‑human apes, reinforcing the notion that early hominins retained certain primitive growth tactics even as their bodies evolved.
What This Means for Modern Anthropology
Understanding how early humans diversified informs how we interpret the modern human lineage. The research demonstrates:
- The presence of multiple bipedal strategies and the evolutionary plasticity that preceded the modern upright posture.
- The importance of dietary niche partitioning for species survival in a shared environment.
- That ecological pressures from the distant past echo present challenges, particularly in the context of rapid climate change.
Alex Haile‑Selassie notes that “We can’t fully understand the present or future without understanding the past.” The data gathered from the Burtele site offers a window into how species adapt—or fail to adapt—to environmental shifts, a reality that resonates with today’s global ecological concerns.
How to Engage with this Research
Curious about the origins of human evolution? We encourage you to dive deeper into ASU’s extensive web of research publications and to follow their Institute of Human Origins’ updates. Understand the tools—like micro‑CT scanning—and learn how they contribute to our broader knowledge base.
Further Reading and Resources
- Nature paper: New finds shed light on diet and locomotion in A. deyiremeda
- Lucy: The Fossil That Sparked Homo Evolution Research
- Institute of Human Origins at Arizona State University
If you are a student interested in pursuing a degree in anthropology or a research assistantship at ASU, consider submitting your application to the College of Liberal Arts and Sciences. The university’s interdisciplinary approach provides a dynamic environment for upcoming scholars.
Call for Engagement
We value your perspective. Feel free to share your thoughts in the comments below and join the conversation about how early hominins interacted with their world.
For related insights, browse our anthropology article archive or explore the ASU research highlights page. Scheduling a complimentary virtual tour of the findings collection could broaden your understanding of the field’s current direction.
