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Saturday, April 10, 2010

2-million-year-old Fossils Offer Look At Human Evolution

Scientists say the skeletons of a woman and boy could be one of the most important finds of recent times. A discovery by a 9-year-old led to finding the pair, dubbed Australopithecus sediba.

The middle-aged woman and the young boy, perhaps her son or simply another member of her tribe, were out hunting on the African plains or maybe looking for water in the midst of a drought when they fell into a sinkhole, dying almost instantly.

Shortly thereafter, a monsoon or a flood washed them into a deeper basin, where they were covered with mud and rapidly fossilized.

In 2008, nearly 2 million years later, another boy, 9-year-old Matthew Berger, discovered part of their skeletons outside the Malapa cave north of Johannesburg, South Africa, a find that experts have dubbed one of the most important of recent times.

Matthew was accompanying his father, paleoanthropologist Lee R. Berger of the University of the Witwatersrand in Johannesburg, who had used images from Google Earth to identify caves in the Cradle of Humankind World Heritage Site that might hold fossil deposits.

On his first visit to the Malapa cave, Berger took Matthew and suggested that the boy look around outside for fossils. Within 15 minutes, the boy returned carrying a block of stone bearing a hominid collarbone and a jawbone that had apparently been thrown out of the cave by miners.

Excited by Matthew's discovery, a team led by Berger began excavating the cave and found the rest of that skeleton, which appears to be that of an 11-to-12-year-old boy, and the skeleton of a woman in her mid-30s.

The hominid pair may be direct ancestors of humans or they may be from a closely related branch on the human evolutionary tree, South African researchers reported Thursday in the journal Science.

Either way, experts agree that the rare discovery of nearly intact skeletons provides a look at evolution during what is considered one of the most significant periods of human development, when hominids were changing from the ape-like genus known as Australopithecus into the more modern forms we now know as Homo.

The skeletons are the only complete specimens that fall between the Australopithecus afarensis known as Lucy, dating from 3 million years ago, and the Homo erectus known as Turkana boy, dating from 1.5 million years ago.

"This give us a good chance to look at the rates of change of various parts" of the body, said biological anthropologist William Kimbel of Arizona State University, who was not involved in the discovery. It is exceptionally rare to get such insights from single individuals in which all the body parts are together, he said.

"There are very few things that we can call a skeleton from that time period," said biological anthropologist Christopher Ruff of Johns Hopkins University School of Medicine, who was also not involved in the research. Most often, researchers discover isolated craniums, jawbones or limbs and must extrapolate what the species looked like.

The research process is very much like the ancient tale of the seven blind men who each touch a different part of an elephant and draw widely differing conclusions about the beast's shape, Ruff said. The new specimens are important because they provide a look at the whole elephant.

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