An amazing fossil find in Ethiopia shows that the genus Homo was around 2.8 million years ago, which is 400,000 years earlier than scientists had previously estimated, according to an international team of anthropologists and geoscientists.
The fossil, a lower jaw with five teeth, was discovered in the Ledi-Geraru archeological site in Afar Regional State, Ethiopia, by Chalachew Seyoum, an ASU graduate student from Ethiopia.
The genus Homo (hominoids) denotes a group of Hominids that includes modern humans (Homo sapiens) as well as some extinct species. ‘Homo’ is Latin for ‘man’. Hominids are a biological family including humans, extinct human-like species, and the great apes (chimps, gorillas, orangutans and bonobos).
Fossilized jawbone and teeth of an early human dating back to 2.8 million years ago. (Photo: Science)
Two studies have been published in this week’s online issue of the academic journal Science.
The mandible (jawbone) fossil, known as LD 350-1, discovered in 2012, dates back to 400,000 years before any other human fossils previously found.
Scientists have been trying to find African fossils pointing to the earliest phases of Homo lineage. Until this latest find, none of the scarce specimens dating back to between 2.5 million and 3 million years ago were in good condition.
Erin N. DiMaggio, a research associate at the College of Earth and Mineral Sciences at Penn State, said:
“The record of hominin evolution between 3 and 2.5 million years ago is poorly documented in surface outcrops, particularly in Afar, Ethiopia.”
This lack of documentation means nobody has been able to pinpoint exactly when the Homo lineage evolved into modern humans.
This Ledi-Geraru fossil provides clues to changes in the jaw and teeth in Homo only 200,000 years after the last known occurrence of Australopithecus afarensis (“Lucy”) from the nearby Hadar site.
The back molar teeth of the Ledi-Geraru fossil, being smaller than those of other ancient humans that lived in the area, show that it belonged to a modern human.
According to Professor William Kimbel, director of the Institute of Human Origins at Arizona State University, modern human’s molars are smaller than those of their ancient ancestors.
Different views of the LD 350-1 mandible. (Photo credit: William Kimbel)
In an interview with the BBC, Prof. Kimbel said:
“Previously, the oldest fossil attributed to the genus Homo was an upper jaw from Hadar, Ethiopia, dated to 2.35m years ago.”
“So this new discovery pushes the human line back by 400,000 years or so, very close to its likely (pre-human) ancestor. Its mix of primitive and advanced features makes the Ledi jaw a good transitional form between (Lucy) and later humans.”
Climate change and evolution
Did climate change get us to walk upright?
Climate change may also have been a factor in getting our ancestral tree dwellers onto the ground and walking on two legs, the researchers believe.
Professor Kaye E. Reed, who works at the Institute of Human Origins, Arizona State University, said:
“We can see the 2.8 million-year-old aridity signal in the Ledi-Geraru faunal community. But it’s still too soon to say that this means climate change is responsible for the origin of Homo. We need a larger sample of hominin fossils and that’s why we continue to come to the Ledi-Geraru area to search.”
“Late Pliocene fossiliferous sedimentary record and the environmental context of early Homo from Afar, Ethiopia,” Erin N. DiMaggio, Christopher J. Campisano, Guillaume Dupont-Nivet, Lars Werdelin, Kaye E. Reed, John Rowan, Alan L. Deino, Faysal Bibi, Margaret E. Lewis, Antoine Souron, and J. Ramón Arrowsmith. Science aaa1415. Published online 4 March, 2015 [DOI:10.1126/science.aaa1415].
“Early Homo at 2.8 Ma from Ledi-Geraru, Afar, Ethiopia,” Brian Villmoare, John Rowan, David R. Braun, William H. Kimbel, Chalachew Seyoum, J. Ramon Arrowsmith, Christopher J. Campisano, Erin DiMaggio, and Kaye E. Reed. Science aaa1343. Published online 4 March, 2015 [DOI:10.1126/science.aaa1343].
Video – Discovery of the Oldest Human Fossil