Lower jaw fossil of the new hominin species.
Image credit: Yohannes Haile-Selassie,
Cleveland Museum of Natural History
Writing in the journal Nature, Dr. Yohannes Haile-Selassie, curator of physical anthropology at the Cleveland Museum of Natural History in Ohio, and colleagues describe how they recovered the upper and lower jaw fossils of a new human ancestral species believed to have lived 3.3 million to 3.5 million years ago.
The discovery was made in the Woranso-Mille area of the Afar region of Ethiopia, the region that gives its name to the famous Lucy species, Australopithecus afarensis. Dr. Haile-Selassie notes:
"The new species is yet another confirmation that Lucy's species, Australopithecus afarensis, was not the only potential human ancestor species that roamed in what is now the Afar region of Ethiopia during the middle Pliocene."
The newly discovered hominin has been given the name Australopithecus deyiremeda - "deyiremeda" means close relative in the language of the Afar people.
Hominins include modern humans, extinct human species and all our direct ancestors.
Lucy's species lived some 2.9 million to 3.8 million years ago, and until recently was thought to be our only hominin ancestor, but it is becoming clearer that this is not the case.
Evidence of more than one human ancestral species living over 3 million years ago
The newly discovered species differs from Lucy's in terms of the shape and size of its teeth - which are more thickly enameled, and its lower jaw - which has a more robust structure. The teeth nearer the front are also smaller than Lucy's, suggesting A. deyiremeda probably had a different diet.
The researchers say the fossils also show evidence of tooth and jaw traits that were thought to have appeared much later in the human family tree.
Dr. Haile-Selassie says the discovery offers the most conclusive evidence for the existence of more than one closely related early human ancestor species living more than 3 million years ago.
For a long time, it was thought that humans descended in a straight line from one pre-human species living 3 million to 4 million years ago. This theory was backed up by the fossil record - including the discovery of Lucy - until the end of the 20th century.
But then, the new century brought some surprises - researchers discovered Kenyanthropus platyops in Kenya and Australopithecus bahrelghazali in Chad. Both these species date from Lucy's period - challenging the idea that humans descended from a single hominin species.
Researchers have not assigned the 'Burtele foot' to the new species
At first, scientists were highly sceptical following the discoveries in Kenya and Chad. But some started to change their view when in 2012, Dr. Haile-Selassie announced the discovery of the 3.4 million-year-old Burtele partial foot fossil, confirming the likelihood of multiple hominin species living at the same time 3 million to 4 million years ago.
Daniel Lieberman, an anthropologist at Harvard University said at the time Dr. Haile-Selassie announced the discovery that the Burtele foot is "very much like the Ardipithecus foot, which I believe had many hominin features, so it's likely to be a hominin."
While several features of the Burtele foot confirm that it is truly a hominin, and despite the similarity in geological age and close geographic proximity, the researchers have not assigned the partial foot to the new species due to lack of clear association - there are no skull or dental elements to go with the foot.
Nevertheless, the new discovery adds to the fossil evidence from the Woranso-Mille study area that at least two, if not three, early human species were around at the time of Lucy, the researchers note.
Dr. Haile-Selassie says the new species "takes the ongoing debate on early hominin diversity to another level," and adds:
"Some of our colleagues are going to be skeptical about this new species, which is not unusual. However, I think it is time that we look into the earlier phases of our evolution with an open mind and carefully examine the currently available fossil evidence rather than immediately dismissing the fossils that do not fit our long-held hypotheses."
He and his colleagues say the growing evidence of multiple species raises important questions about how our early ancestors coexisted, shared their environment and resources.
The following video gives an account of the find and its implications, and includes comments from Dr. Haile-Selassie.
Meanwhile, MNT reports how recently discovered 430,000-year-old skull fractures found in a cave in the Atapuerca Mountains of northern Spain may represent the earliest case of murder in humans.