Ancient Foot Fossil Identifies New Early Human Species

Discovery of an Enigmatic Ancient Foot FossilThanks to a series of newly uncovered fossil bones, researchers have successfully connected a mysterious 3.4-million-year-old hominin foot, originally discovered back in 2009, with a distinct species separate from the well-known fossil known as Lucy. This

Discovery of an Enigmatic Ancient Foot Fossil

Thanks to a series of newly uncovered fossil bones, researchers have successfully connected a mysterious 3.4-million-year-old hominin foot, originally discovered back in 2009, with a distinct species separate from the well-known fossil known as Lucy. This important connection reinforces the idea that multiple early human ancestor species coexisted in the same geographic area during the same era, highlighting greater diversity among our distant relatives than previously understood.

Back in 2009, an international research group headed by Arizona State University paleoanthropologist Yohannes Haile-Selassie recovered eight foot bones belonging to an ancient human forebear from layers of sediment dated to approximately 3.4 million years ago. These remains came from the Afar Rift region in Ethiopia at the Woranso-Mille paleontological location. The specimen, referred to as the Burtele foot, was later formally described in a scientific paper published during 2012.

Upon locating the foot remains in 2009 and sharing the findings publicly in 2012, the team recognized right away that this particular foot differed significantly from the species associated with Lucy, known scientifically as Australopithecus afarensis. That species is extensively documented from fossils found in the same general time period, according to Haile-Selassie, who serves as director of the Institute of Human Origins and holds a professorship at the ASU School of Human Evolution and Social Change.

Linking the Burtele Foot Remains to Australopithecus deyiremeda

At the time the Burtele foot was initially analyzed and published, several teeth had already been collected from the broader surrounding area. Researchers remained uncertain, however, whether those teeth originated from precisely the same sedimentary layer as the foot bones. In 2015 the group formally described a new species from this locality called Australopithecus deyiremeda, yet they refrained from directly associating the Burtele foot with it at that stage, even though certain fossils lay in close proximity to the foot site.

Through continued fieldwork spanning the following decade and the recovery of additional specimens, the scientists gradually assembled stronger supporting evidence. Haile-Selassie noted that sufficient material now exists to confidently attribute the Burtele foot to the species Australopithecus deyiremeda with greater certainty than before.

Evidence of Two Coexisting Hominin Species

Assigning the Burtele foot to a particular species forms only one chapter in a broader narrative. The Woranso-Mille locality stands out because it supplies compelling proof that two closely related hominin species inhabited the identical region simultaneously. The Burtele foot, now tied to Australopithecus deyiremeda, exhibits more primitive characteristics compared to the feet belonging to Lucy's species, Australopithecus afarensis. In contrast to Lucy, the Burtele foot retained an opposable big toe suited for arboreal movement. Nevertheless, when moving across the ground, Australopithecus deyiremeda remained bipedal and appears to have propelled itself mainly using the second toe instead of the big toe, differing from the typical gait pattern observed in modern humans.

The presence of an abducted big toe in the earlier species Ardipithecus ramidus came as a considerable surprise because at 4.4 million years ago an early hominin ancestor still possessed an opposable big toe, an unexpected trait. Then roughly one million years afterward at 3.4 million years ago, the Burtele foot appears, which proves even more unexpected. This timeframe coincides with species such as Australopithecus afarensis whose individuals were fully adapted to upright walking with an adducted big toe. The implication is that bipedal locomotion among these early human ancestors manifested in multiple distinct forms rather than following a single uniform pattern until much later periods.

Isotopic Analysis Revealing Dietary Differences

To gain deeper insight into the diet of Australopithecus deyiremeda, Naomi Levin from the University of Michigan examined eight out of twenty-five teeth recovered from the Burtele locality through isotopic methods. The procedure starts by thoroughly cleaning the tooth surface before carefully extracting only the enamel portion for detailed examination.

Sampling occurs using a dental drill fitted with a very small bit measuring less than one millimeter, identical to equipment employed by dentists during routine procedures. Small quantities of powder are removed and stored in plastic vials before transport back to the laboratory at the University of Michigan for isotopic analysis. The resulting data proved surprising because while Lucy's species displayed a mixed diet incorporating both C3 resources from trees and shrubs along with C4 plants such as tropical grasses and sedges, Australopithecus deyiremeda depended more extensively on C3 resources alone.

Establishing Fossil Ages and Ancient Environments

Determining the precise age of the fossils and reconstructing the ancient landscapes where these hominins lived represented another essential component of the investigation. Mapping how fossil-bearing layers relate across space and time assists scientists in understanding the timing and environmental conditions under which each species existed. Extensive careful fieldwork at Woranso-Mille has clarified relationships among different fossil layers, which proves vital for interpreting when and in what settings the various species lived, as explained by Beverly Saylor of Case Western Reserve University who directed the geological studies confirming the stratigraphic link between the foot and Australopithecus deyiremeda.

Juvenile Jawbone Providing Developmental Insights

In addition to the twenty-five teeth from Burtele, the team also recovered the jaw of a juvenile individual that tooth anatomy clearly assigned to Australopithecus deyiremeda. This jaw contained a full complement of baby teeth already erupted along with numerous adult teeth still forming within the lower jawbone. Researchers applied CT scanning technology to visualize the developing teeth. Because tooth formation closely correlates with overall growth patterns, this data enabled the team to estimate that the young individual was approximately 4.5 years old at death. For a juvenile hominin of this developmental stage, clear traces emerged of a disconnect in growth timing between the front teeth known as incisors and the back chewing teeth called molars, resembling patterns seen in living apes and other early australopiths including Lucy's species. Despite increasing recognition of diversity among these early australopith species in terms of body size, dietary preferences, locomotor abilities, and anatomical features, they appear remarkably consistent in the manner of their growth and development.

Understanding Coexistence Among Ancient Hominins

By integrating data concerning locomotion, diet, and environmental context, scientists are developing fresh perspectives on how distinct hominin species could occupy the same region without one driving the other toward extinction. Variations in walking styles, climbing behaviors, and feeding strategies likely permitted them to utilize the landscape in different ways. All of the research aimed at understanding ecosystems from millions of years ago extends beyond mere curiosity about human origins. It reflects a desire to comprehend our present circumstances and future trajectory as well. Without grasping our past we cannot fully appreciate the present or anticipate what lies ahead. Events from the distant past mirror processes observable today, including repeated instances of climate change during the times of Lucy and Australopithecus deyiremeda. Lessons drawn from that ancient period may help address some of the most severe consequences of contemporary climate shifts.