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THE ANATOMICAL RECORD 266 249 257 2002 Missing Omo L338y 6 OccipitalMarginal Sinus Drainage Pattern Ground Sectioning Computer Tomography Scanning and the Original Fossil Fail to Show It RALPH L HOLLOWAY 1 MICHAEL S YUAN 2 DOUGLAS C BROADFIELD 3 4 DAVID DEGUSTA 5 GARY D RICHARDS 6 7 ADAM SILVERS 8 JILL S SHAPIRO 1 9 AND TIM D WHITE5 1 Department of Anthropology Columbia University New York New York 2 Department of Anatomy and Cell Biology School of Dental and Oral Surgery Columbia University New York New York 3 Department of Anthropology Florida Atlantic University Boca Raton Florida 4 Department of Cell Biology and Anatomy Mount Sinai School of Medicine New York New York 5 Department of Integrative Biology and Laboratory for Human Evolutionary Studies Museum of Vertebrate Zoology University of California Berkeley Berkeley California 6 Laboratory for Human Evolutionary Studies Museum of Vertebrate Zoology University of California Berkeley Berkeley California 7 Department of Anatomy University of the Pacific School of Dentistry San Francisco California 8 Department of Radiology Mount Sinai Hospital New York New York 9 School of Continuing and Professional Studies New York University New York New York ABSTRACT The Omo L338y 6 occipital region has been recently studied by White and Falk 1999 who claim that it shows a readily identifiable enlarged left occipital marginal sinus O M These observations are contrary to the direct observations of previous investigators Rak and Howell 1978 Kimbel 1984 Holloway 1981 Holloway 1988 White and Falk 1999 further argue that the presence of this enlarged O M strongly suggests that the Omo L338y 6 hominid was indeed a robust Australopithecus We used direct sectioning and CT scanning to analyze magnified sections of a high quality first generation cast of the newly cleaned original fossil These methods fail to show any evidence of a morphological landmark that can be interpreted as an enlarged O M either as an eminence or a sulcus In contrast the same techniques used with both SK 1585 and OH5 robust Australopithecus with an enlarged O M show extremely visible and palpable enlarged O M s Examination of the original Omo fossil confirms that it lacks an O M This evidence clearly shows that an enlarged O M cannot be identified on either the original fossil or a first generation cast although this does not rule out the possibility that the Omo L338y 6 hominid was a robust Australopithecus We believe that the differences between observers regarding this feature are most probably due to displacement caused by a crack and the different source materials employed i e the difference between a first generation cast of the original fossil and a third or fourth generation cast of the endocast made two decades ago Anat Rec 266 249 257 2002 2002 Wiley Liss Inc Key words occipital marginal sinus O M drainage pattern brain evolution Australopithecus brain endocasts computer tomography ground sectioning In 1981 one of us R L H



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