A team led by Cleveland researchers has discovered a fossil cranium that puts a face on an early human ancestor which had only been known by bone fragments.
The finding also shows that this human ancestor lived at the same time as the species made famous by the Lucy fossils.
The skull, about the size of a large grapefruit, is 3.8 million years old. That puts it within the window of time when Lucy’s species (Australopithecus afarensis) roamed east Africa.
He says it provides a much more complete picture of this ancient hominin known as Australopithecus anamensis.
“All we had were some teeth, the upper jaw and lower jaw fragments, without the midface, without the cranium," says Haile-Selassie, "now we have the whole thing.”
Haile-Selassie says Australopithecus anamensis is a likely forebear to Lucy’s species, but it had not been previously known that the two species overlapped by 100,000 years. The oldest evidence of Lucy's species dates back to 3.9 million years ago.
This discovery changes the way scientists had postulated the evolutionary transition from anamensis to afarensis. He says we now know they split from each other and coexisted for a time.
“A small population of Australopithecus anamensis could isolate itself from the main population and undergo a lot of changes through time," says Haile-Salassie, "which eventually accumulated to make it different from the parent population."
"That’s one way of speciation not only in hominins but also in a lot of other animal groups,” he says.
Haile-Selassie says by around 3.3 million years ago, this region of Africa was home to 3 or 4 early hominins.
They include Lucy's species, Au. afarensis, along with the closely related species Australopithecus deyiremeda, Australopithecus bahrelghazali, and Kenyanthropus platyops, along with remnant populations of ancient tree-dwelling hominins related to Ardipithicus.
This menagerie of early human ancestors creates a confusing picture of the dawn of humankind, according to Haile-Selassie.
"So the big challenge that we have now is that we need to figure out which one of these Australopithecus species actually gave rise to the genus Homo," he says.
The earliest evidence we have of the genus Homo is from a 2.8 million-year-old jaw bone, according to Haile-Selassie.
Analysis of mineral evidence by Case Western Reserve University's Beverly Saylor shows the individual lived near a lake in otherwise semi-arid scrubland. Her team also determined that 3.8 million-years-ago is the precise age of the fossil cranium.
The findings are published in this week’s online edition of the journal Nature.