A "Missing Link" Fossil Adds "Foliage" to the Early Human Ancestor Family Tree
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East African paleo-anthropological sites have yielded 2.5- million-year-old fossils of a possible direct human ancestor. "These fossils are providing exciting new evidence about the long sought evolutionary connection between species of early hominids, like Australopithecus, and the genus Homo," said National Science Foundation (NSF) Physical Anthropology Program Director Mark L. Weiss.
The cranial, leg, and arm bone fossils of this newly discovered species were unearthed in Ethiopia by a team of scientists led by NSF-supported anthropologist Tim White of the University of California-Berkeley and Berhane Asfaw of Ethiopia, and are publicized in the April 23 issue of Science magazine. Significantly, the femur is elongated-a million years before hominid fossil evidence shows forearm shortening-which, together with shortened forearm, creates the familiar modern human limb proportions.
Similar-age animal fossils discovered in the same area, the Middle Awash study area in the Afar desert, indicate that the meat and bone marrow of large mammals (antelopes and horses, specifically) were obtained with the world's earliest stone tool technology, according to a companion article in Science. White cautioned that "we cannot yet conclusively link the new species with the butchery or the more modern limb proportions." Both sets of fossils were dated using the argon-argon radioisotope method as well as biochronology and paleomagnetism. The same research team had discovered the earliest-known hominid, the 4.4-million-year-old Ardipithecus, at the nearby Aramis site in 1992.
These fossil finds are significant for several reasons, according to the discoverers. "The hominid fossils may allow us to add a new member to the human evolutionary family tree," said Weiss, "and the evidence regarding the use of stone tools in food processing indicates an early reliance on meat in hominid diet. This adaptation would have allowed them to venture into new habitats and ultimately into new continents."
According to the discoverers, the new Ethiopian hominid fossils, named Australopithecus garhi, help fill a serious void in the east African record of human origins that spans a duration of between 2 and 3 million years ago. This void has made it impossible to settle scientifically the relationship between the 1.8-million-year-old Homo habilis and earlier ape-like Australopithecus africanus.
Increasingly, the focus on African early hominid fossil wealth has centered on Ethiopian sites in contrast to the last few decades' focus on better-known productive sites in Tanzania, Kenya and elsewhere. "With the publication of these new results, and with a record spanning five million years, Ethiopia's Middle Awash has become the world's most important single site for studying human origins and evolution," said White.
The research in the Middle Awash area is supported mainly by the National Science Foundation. Additional support comes from the Institute of Geophysics and Planetary Physics of the University of California's Los Alamos National Laboratory and several other institutions mentioned in the published Science articles. The international research team includes archaeologists, geologists and paleontologists from diverse institutions in 13 countries.
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