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. Anat Rec 266:249–257, 2002. © 2002 Wiley‐Liss, Inc.