Glenoid Fossa Area Size

The size of the fossa is defined as the square root of the area of the triangular plane between: (a) tips of the postglenoid process; (b) entoglenoid process; and (c) the articular tubercle (see Strait, 2001). While the size (area) of the glenoid fossa may be considered by some to be similar to or strongly correlated with glenoid fossa depth (character 24), we argue that this feature, as defined by Strait (2001) is distinct, for size (area) need not correlate with depth. This is reinforced by the character state allocations shown in Appendix Table 1. For example, while Gorilla and P. walkeri both have a large glenoid fossa, in terms of depth they are distinct, because Gorilla has the intermediate condition, while in P. walkeri it is shallow. The same character states and allocations suggested by Strait (2001) are used here.

Pongo (n = 2) falls between the values generated for Pan (n = 2) and Gorilla (n = 3); however, it was close to the value generated for a cast of KNM-WT 17000. Thus, Pongo is allocated here as having a large glenoid fossa. The primitive condition is represented by a large fossa as seen in Pongo, Gorilla, P. walkeri, P. robustus, and P boisei (= 0). An intermediate state is defined for Pan, Praeanthropus, Australopithecus, K. rudolfensis, H. habilis, and H. ergaster (= 1). A small fossa is defined for H. sapiens only (= 2).

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