Occipitomarginal Sinus

The development of this derived vascular pattern has been equated with the changing gravitational pressures associated with bipedalism (Falk & Conroy, 1984; Falk, 1986, 1988). It is suggested that this early pattern would enable increased flow of blood to the vital organs, given the changed posture. Tobias (1967), however, suggests that the patterns identified in these hominins may be associated with the early growth during ontogeny of the cerebellum, which may have forced blood into the marginal sinus system, which then became the established path of blood supply during adulthood. In either case it is of developmental and functional significance because the likelihood of heritability is strong.

An occipitomarginal sinus is absent in Pongo, Gorilla, Pan, P. walkeri (Walker et al., 1986; Skelton & McHenry, 1992), K. platyops (M.G. Leakey et al., 2001), K. rudolfensis (Kimbel, 1984; Tobias, 1991), and H. habilis (Aiello & Dean, 1990; Tobias, 1991; Strait et al., 1997). The condition in Australopithecus and H. sapiens is that it is intermediately expressed (= 1) (Kimbel, 1984; Aiello & Dean, 1990). An occipitomarginal sinus is, however, most frequently present in Praeanthropus, P. boisei, and P robustus (= 2) (Falk, 1986, 1988; Skelton & McHenry, 1992; Strait et al., 1997).

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