Supraglenoid Gutter Development

This feature is defined by an index of supraglenoid gutter width divided by bi-supramastoid breadth. Pongo has a mean index of 19.8 (n = 3), Gorilla has a mean of 28.3 (n = 3), and Pan has a mean of 19.4 (n = 2). Three states are recognized here. The first is defined as wide (= 0) in Gorilla and P walkeri (with an index of 27.9); an intermediate stage (= 1) is defined by Pongo, Pan, P. robustus (SK 48 = 24.2), and P boisei (KNM-ER 406 = 22.9, KNM-ER 732 = 21.4, and OH 5 = 24.3). A narrow gutter (= 2) defines Australopithecus (Sts 5 = 14.4), H. habilis (OH 24 = 10.0, KNM-ER 1813 = 15.0), H. ergaster (KNM-ER 3733 = 13.4), and H. sapiens. While no data were available for K. rudolfensis, it can best be considered very much reduced.

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