Missing Omo L338y-6 occipital-marginal sinus drainage pattern: ground sectioning, computer tomography scanning, and the original fossil fail to show it.
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.
Holloway
Ralph L
RL
Department of Anthropology, Columbia University, New York, New York 10027, USA. rlh2@columbia.edu
Yuan
Michael S
MS
Broadfield
Douglas C
DC
Degusta
David
D
Richards
Gary D
GD
Silvers
Adam
A
Shapiro
Jill S
JS
White
Tim D
TD
D000818:Animals; D000885:Anthropology, Physical; D000886:Anthropometry; D005075:Biological Evolution; D001921:Brain / Q000033:anatomy & histology*; D002965:Classification; D003392:Cranial Sinuses / Q000033:anatomy & histology*; D005580:Fossils; D015186:Hominidae / Q000033:anatomy & histology*; D006801:Humans; D009777:Occipital Bone / Q000033:anatomy & histology*; D015898:Tomography Scanners, X-Ray Computed