The Ardipithecus ramidus Skull and Its Implications for Hominid Origins

The Ardipithecus ramidus Skull and Its Implications for Hominid Origins,Science,Gen Suwa,Berhane Asfaw,Reiko T. Kono,Daisuke Kubo,C. Owen Lovejoy,Tim

The Ardipithecus ramidus Skull and Its Implications for Hominid Origins   (Citations: 3)
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he key feature that distin- guishes Homo sapiens from other primates is our unusu- ally large brain, which allows us to communicate, make tools, plan, and modify our environment. Un- derstanding how and when our cognitive ability evolved has been a special focus in anthropology and, more recently, genetics. Fossil hominid skulls provide direct evi- dence of skull evolution and infor- mation about diet, appearance, and behavior. Skulls feature promi- nently in the characterization of species, in taxonomy, and in phy- logenetic analyses of both extinct and living primates. Unfortunately, hominid skulls are relatively rare in the fossil record. A number of partial skulls and crania (skulls without a lower jaw) of early Homo and its predecessor, Australopithecus (which lived ~1 to 4 million years ago), have been recovered, but relatively few are complete enough for extensive comparisons. One surprisingly com- plete but distorted cranium from 6 to 7 million years ago was discov- ered in central Africa (Chad). This fossil, Sahelanthropus tchadensis (a.k.a. "Toumaï "), is thought by many to represent the earliest known hominid, although some have argued that it is a female ape. The Ardipithecus ramidus skull is of particular interest because it predates known Australopithecus and thereby illuminates the early evolution of the hominid skull, brain, and face. The Ar. ramidus skull was badly crushed, and many of its bones were scattered over a wide area. Because the bones were so fragile and damaged, we imaged them with micro-computed tomography, making more than 5000 slices. We assembled the fragments into more than 60 key virtual pieces of the braincase, face, and teeth, enough to allow us to digitally reconstruct a largely complete cranium. The fossil skulls of Australopithecus indicate that its brain was ~400 to 550 cm 3 in size, slightly larger than the brains of modern apes of similar body size and about a third of those of typical Homo sapi- ens. Its specialized craniofacial architecture facilitated the production of strong chewing forces along the entire row of teeth located behind its canines. These postcanine teeth were enlarged and had thick enamel, consistent with a hard/tough and abrasive diet. Some species exhibited extreme manifestations of this specialized chewing appara- tus and are known as "robust"
Journal: Science , 2010
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