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Early human ancestors had lots of company, fossils reveal (+video)

Our apelike forbears shared East Africa with lots of other hominid species, according to an analysis of fossils discovered in northern Kenya.

By Charles ChoiLiveScience Contributor / August 8, 2012

Four decades ago, in 1972, the Koobi Fora Research Project (KFRP) discovered the enigmatic fossilized skull known as KNM-ER 1470, or "1470" for short, which ignited a now long-standing debate about how many different species of early Homo lived alongside Homo erectus during the Pleistocene epoch. Shown here, 1470's cranium combined with the new lower jaw KNM-ER 60000; both are thought to belong to the same species. The lower jaw is shown as a photographic reconstruction, and the cranium is based on a computed tomography scan.

© Photo by Fred Spoor

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New fossils from the dawn of the human lineage suggest our ancestors may have lived alongside a diversity of extinct human species, researchers say.

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Although modern humans, Homo sapiens, are the only human species alive today, the world has seen a number of human species come and go. Other members perhaps include the recently discovered "hobbit" Homo floresiensis.

The human lineage, Homo, evolved in Africa about 2.5 million years ago, coinciding with the first evidence of stone tools. For the first half of the last century, conventional wisdom was that the most primitive member of our lineage was Homo erectus, the direct ancestor of our species. However, just over 50 years ago, scientists discovered an even more primitive species of Homo at Olduvai Gorge in Tanzania they dubbed Homo habilis, which had a smaller brain and a more apelike skeleton.

Now fossils between 1.78 million and 1.95 million years old discovered in 2007 and 2009 in northern Kenya suggest that early Homo were quite a diverse bunch, with at least one other extinct human species living at the same time as H. erectus and H. habilis.

"Two species of the genus Homo, our own genus, lived alongside our direct ancestor, Homo erectus, nearly 2 million years ago," researcher Meave Leakey at the Turkana Basin Institute in Nairobi, Kenya, told LiveScience.

A skull known as KNM-ER 1470, found in 1972 in Kenya, was at the center of the debate over the number of species of early Homo living nearly 2 million years ago. It had a larger brain and a flatter face than H. habilis, leading some researchers to declare it a distinct species they dubbed Homo rudolfensis. [See Photos of the New Homo Fossils]

However, making comparisons between these fossils was difficult, because no single purported H. rudolfensis specimen contained both the face and the lower jaw, details needed to see if it was indeed separate from H. habilis. Any supposed differences between H. habilis and H. rudolfensis might, for instance, have been due to variations between the sexes of a single species.

The newly discovered face and lower-jaw fossils, uncovered within a radius of just more than 6 miles (10 kilometers) from where KNM-ER 1470 was unearthed, now suggest that KNM-ER 1470 and the novel finds are indeed members of a distinct species of early Homo that stands out from others with its uniquely built face.

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