Following on from the previous node is the emergence of the chimpanzee lineage from the later Plio/Pleistocene hominids. Nine derived features define this hominid. The temporal lines are defined by a more moderate anteromedial incursion of the frontal bone, which is clearly influencing the reduced development of sagittal crests in males. Temporal fossa size has decreased. Petrous orientation is less sagittally aligned. The glenoid fossa is more shallow and reduced in overall size. The zygomatic/malar tends to have an anterior slope. The mental foramen of the mandible opens anterosuperiorly and the extramolar sulcus has decreased in size. The immediate common ancestor to the chimpanzee and later hominids has a reduced temporalis and TMJ development, obviously associated with dietary and masticatory considerations.

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