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| Professor Lluís Gibert, from the University of Barcelona, is the only expert from a European institution participating in an international study based on the analysis of the bones of a fossilized foot and teeth that has revealed how Australopithecus deyiremeda, a human ancestor that coexisted more than three million years ago with Australopithecus afarensis — the famous Lucy — on the plains of East Africa, moved and fed. Photo Credit: Courtesy of University of Barcelona |
In 2009, scientists found eight bones from the foot of a human ancestor in layers of ancient sediment at the Woranso-Mille site in the central Afar region of Ethiopia. The fossil remains, known as the Burtele Foot, were discovered by a team led by paleoanthropologist Yohannes Haile-Selassie, from Arizona State University (United States), but were not assigned to any fossil species of a human ancestor from the African continent.
The international team of experts includes Professor Lluís Gibert, from the Faculty of Earth Sciences of the University of Barcelona, who is the only researcher from a European institution to sign the study. Geological analyses were decisive for dating and linking this foot to the remains of A. deyiremeda.
A fossilized foot that could not have belonged to Lucy
A. deyiremeda is a human ancestor. This scientific breakthrough put an end to the debate over whether Australopithecus afarensis — the famous Lucy discovered in Ethiopia by Donald Johanson and Yves Coppens in 1974 — coexisted with other hominid species in the Middle Pliocene.
“The site of Woranso-Mille is significant because it is the only site where scientists have clear evidence showing two related hominin species co-existed at the same time in the same area. When we found the foot in 2009 and announced it in 2012, we knew that it was different from Lucy’s species, Australopithecus afarensis, which is widely known from that time,” said Yohannes Haile-Selassie, director of the Institute of Human Origins and professor at the School of Human Evolution and Social Change (United States).
The different faces of bipedalism in human evolution
Burtele Foot is more primitive than the feet of Lucy’s species, which was fully bipedal. It retained an opposable big toe — important for climbing — and the toes were longer and more flexible, also suitable for grasping. But when A. deyiremeda walked on two limbs, it probably pushed off with the second toe and not the big toe, as we modern humans do.
“However, it is not common practice in our field to name a species based on postcranial elements — meaning elements below the neck — so we were hoping that we would find something above the neck in clear association with the foot. Jaws and teeth are usually the elements used in species recognition.”
The discovery of Burtele Foot is even more surprising than that of the Ardipithecus ramidus fossil, an early hominid ancestor that still had an opposable big toe 4.4 million years ago. “This is a time when we see species like A. afarensis whose members were fully bipedal with an adducted big toe. So, what that means is that bipedality — walking on two legs — in these early human ancestors came in various forms. The whole idea of finding specimens like the Burtele Foot tells you that there were many ways of walking on two legs when on the ground, there was not just one way until later.”
“Without a geological context and detailed chronology, these fossils would have no scientific value,” says Professor Gibert, from the Department of Mineralogy, Petrology and Applied Geology, who has analyzed the chronostratigraphic and sedimentological context of the fossils found.
How did this Australopithecus feed itself?
A. deyiremeda’s diet was rich in food resources based on trees and shrubs, according to isotopic analysis of eight of the 25 teeth found at the site. Lucy, in turn, expanded this dietary record with the intake of tropical herbs and citrus fruits.
“I was surprised that the carbon isotope signal was so clear and so similar to the carbon isotope data from the older hominins A. ramidus and Au. Anamensis. I thought the distinctions between the diet of A. deyiremeda and A. afarensis would be harder to identify, but the isotope data show clearly that A. deyiremeda wasn’t accessing the same range of resources as A. afarensis, which is the earliest hominin shown to make use of C4 grass-based food resources”, notes Professor Naomi Levin, from the University of Michigan (United States).
In addition to the teeth found in Burtele, the jawbone of a juvenile specimen of the species A. deyiremeda was also discovered. “This jaw had a full set of baby teeth already in position, but it also had a lot of adult teeth developing deep within the bony mandible”, says Gary Schwartz, from the Institute of Human Origins (IHO) and the School of Human Evolution and Social Change.
Using state-of-the-art microCT scanning technology, the team determined that the jaw belonged to a hominid that was about 4.5 years old at the time of death. “For a juvenile hominid of this age, we were able to see clear traces of a disconnect in growth between the front teeth (incisors) and the back chewing teeth (molars), much like what we see in living apes and other early australopithecines, such as Lucy’s species,” Schwartz notes.
“I think the biggest surprise was despite our growing awareness of how diverse these early australopith (i.e., early hominin) species were – in their size, in their diet, in their locomotor repertoires and in their anatomy – these early australopiths seem to be remarkably similar in the manner in which they grew up.”
Knowing the past to understand the present and predict the future
Understanding how these ancient ancestors moved and what they ate provides new insights into how species coexisted at the same time without driving each other to extinction. “All of our research to understand past ecosystems from millions of years ago is not just about curiosity or figuring out where we came from,” Haile-Selassie said. “It is our eagerness to learn about our present and the future as well.”
“If we don’t understand our past, we can’t fully understand the present or our future. What happened in the past, we see it happening today,” he said. “In a lot of ways, the climate change that we see today has happened so many times during the times of Lucy and A. deyiremeda. What we learned from that time could help us mitigate some of the worst outcomes of climate change today.”, concludes Haile-Selassie.
Published in journal: Nature
Title: New finds shed light on diet and locomotion in Australopithecus deyiremeda
Authors: Yohannes Haile-Selassie, Gary T. Schwartz, Thomas C. Prang, Beverly Z. Saylor, Alan Deino, Luis Gibert, Anna Ragni, and Naomi E. Levin
Source/Credit: University of Barcelona
Reference Number: pal112725_01