This character is retained in this analysis because it relates to the vascular system and is thus likely to be of developmental and functional interest. The same character states and species allocations provided by Strait et al.
(1997) have been retained. Four states are recognized. The primitive condition is defined by the foramen opening anterosuperiorly (= 0) as seen in Kenyapithecus (Andrews & Walker, 1976), Pan, and Ardipithecus (Strait & Grine, 2001). This is followed by some intra-species variability (= 1) in Dryopithecus (Begun, 2002), Pongo, Gorilla, Praeanthropus, and Australopithecus (Strait & Grine, 2001). In Graecopithecus and in most specimens of H. sapiens the foramen opens posteriorly (= 2). The foramen opens laterally (= 3) in the "anamensis group," P boisei, P. robustus, K. rudolfensis, H. habilis, and H. ergaster (Strait & Grine, 2001). This feature remains unordered, as its morphocline cannot be ascertained with any degree of certainty.
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