At this node, the last common ancestor between Praeanthropus and later hominins, the articular tubercle again increases in size (homoplasy), and the zygomatic has moved anteriorly. The difference between the premolar and molar complexes has increased. The mandibular symphysis is less receding and the corpus has increased in overall robusticity. Finally, P3 metaconids start to appear and the expansion of the mesiobuccal corner is variable.

Praeanthropus afarensis is marked by a continued reduction in postorbital constriction and an occipitomarginal sinus is present. Also, molar cusps and cristae are more developed, and the buccal cusps continue to move medially away from the buccal edge. There is a continuation of the hominin condition of reduced neuro-orbital disjunction, emphasized by a further reduction in postorbital constriction. The differential pattern of occlusal morphology can be associated with an increase in shearing action, possibly associated with increased consumption of vegetative material from that of its contemporaries and hypothetical ancestor.

The neurological configuration in Praeanthropus has been used to support a close phylogenetic relationship between it and Paranthropus (see Skelton et al., 1986). As we will see, however, this morphology is not present in the presumed ancestor of the Paranthropus clade (P walkeri) and thus must be considered a homoplasy. Indeed, the evolution of this feature can be explained as the result of a number of likely developmental demands not closely associated with phylogenetic considerations. For example, the development of this 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 it may be associated with the early growth during ontogeny of the cerebellum, which may have forced blood into the marginal sinus system, then becoming the established path of blood supply during adulthood.

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