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This node represents that last common ancestor to Ardipithecus and the other more derived hominids. This hypothetical ancestor has an increase in cranial base flexure, and reduction in nuchal plane inclination, articular tubercle, eustachian process, and longus capitis insertion. The basioccipi-tal is reduced in length. Foramen magnum is located more anteriorly and is inclined in a more horizontal position. There is an increase in the frequency of the occipitomarginal sinus. In terms of upper facial features, glabella is broad but not inflated, and the supraorbital sulcus is reduced. Interorbital breadth has increased and nasal bones are projected and expanded. The palate has also increased in breadth. The nasal clivus has increased in length, and its height and the incisive canal are more developed. Upper male canines are reduced in size and there has been an increase in upper molar size. The buccal cusps tend to crowd the occlusal surface. The mandibular symphysis is more robust and the P3 mesiobuccal expansion has decreased.

At this point in human evolution, we see increased flexure of the cranial base. This may be associated with the foramen magnum now moving in a more anterior position and a reduction in lower facial prognathism (and increased palate breadth). At the same time, we see a tendency for male canines to be smaller in size and less daggerlike, while the molars have increased in size. Ardipithecus has two apomorphies — the auditory meatus is now aligned to porion (suggestive of increased cranial base breadth?), and the digastric muscle insertion is now deep and narrow. So far all we can say is that in its preserved morphology, Ardipithecus appears to reflect a distinct pattern of digastric muscle development to that observed in the outgroup, which may also be associated with the differential development of its broader(?) cranial base.

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