Friday, August 10, 2012

DISCOVERY OF NEW FOSSILS REVEALS FAMILY TREE HAS MANY BRANCHES

The discovery of three new fossil specimens, recently announced, is the most compelling evidence yet for multiple lines of evolution in our own genus, Homo, scientists said. The fossils showed that there were at least two contemporary Homo species, in addition to Homo erectus, living in East Africa as early as two million years ago.

Uncovered from sandstone at Koobi Fora, badlands near Lake Turkana in Kenya, the specimens included a well-preserved skull of a late juvenile with a relatively large braincase and a long, flat face, which has been designated KNM-ER 62000 (62000 for short). It bears a striking resemblance to the enigmatic cranium known as 1470, the center of debate over multiple lineages since its discovery in the same area in 1972.

If the 62000 skull showed that 1470 was not a single odd individual, the other two specimens seemed to provide a vital piece of evidence that had been missing. The specimen 1470 had no mandible, or lower jaw. The new finds included an almost complete lower jaw (60000) — considered to be the most complete mandible of an early Homo yet found — and a part of another lower jaw (62000).

The fossils were collected between 2007 and 2009 by a team led by Meave and Louise Leakey, the mother-and-daughter paleoanthropologists of the Koobi Fora Research Project and members of the famous African fossil-hunting family. Dr. Meave Leakey is the wife of Richard Leakey, a son of Louis and Mary Leakey, who produced the early evidence supporting Africa’s central place in early human origins. Mr. Leakey divides his time between Stony Brook University on Long Island, where he is a professor of anthropology, and the Turkana Basin Institute in Kenya.

After looking “long and hard” for fossils to confirm the intriguing features of 1470’s face and show what its teeth and lower jaw were like, Dr. Meave Leakey said this week, “At last we have some answers.”

The real crux of matter, said Susan C. Antón of New York University, a member of the team, is how the discovery shapes the interpretation of 1470’s place in the early world of Homo. “These fossils are anatomically like 1470, and we now have some teeth,” she said. “We are more certain that 1470 was not a one-off, and not everything 1470 is big.”

In their first formal report, Dr. Leakey and her colleagues wrote in the journal Nature, “These three specimens will greatly aid the reassessment of the systematics and early radiation of the genus Homo.”

They, however, chose not to assign the fossils to any existing or new species until more analysis is conducted on contemporary hominids. The 1470 specimen was two million years old; the new face and fragmentary jaw are 1.9 million to 1.95 million years old; the better-preserved lower jaw is younger still, at 1.83 million years old.

Fred Spoor, a member of the discovery team who directed the laboratory analysis, said in a news teleconference that the research showed clearly that “human evolution is not this straight line it was once thought to be.” Instead, East Africa, he said, “was quite a crowded place, with multiple species” with presumably different diets.

Dr. Spoor is a paleoanthropologist at University College London and the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. The lab work was supported by the institute. The fieldwork was financed by the National Geographic Society, and the dating of the fossils, mainly by Craig S. Feibel of Rutgers University, was supported by the Leakey Foundation.

Chris Stringer of the Natural History Museum of London, who had no part in the research, agreed that it looked as if the new discoveries “confirm the distinctiveness of 1470” and “therefore confirm the existence of a distinctive kind of early human around 1.8 to 2.0 million years ago.” But he noted that “there remain many uncertainties” about the 1470 fossil “and whether it might still be just a large specimen of Homo habilis.”

Another problem, Dr. Stringer said, is that in the last three decades, as the number of fossils attributed to habilis has grown, it has become unclear how to define what is and is not a member of that Homo species. Determining if the new fossils belong to rudolfensis or habilis, he said, “would depend on ongoing comparisons with the original fossil assemblage” at Olduvai Gorge in Tanzania, where the first and many other habilis and contemporary specimens have been excavated.




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