Upper incisor morphology of the Late Miocene hominoid Ouranopithecus macedoniensis from Axios Valley (Macedonia, Greece)

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The upper incisor lingual morphology of the late Miocene Greek hominoid Ouranopithecus macedoniensis was almost unknown, as the described earlier maxillary remains preserve only worn incisors. During the most recent excavations in the type locality of Ouranopithecus, Ravin de la Pluie (RPl) of Axios Valley (Macedonia, Greece), four little-worn upper central incisors were recovered. This material and a few additional worn upper incisors, discovered recently, are described and compared in this article. Even though a morphological comparison with the old RPl material, lacking unworn or little worn incisors, is impossible, the metrical comparison and the monospecific character of the RPl hominoid sample suggest that the described incisors can be assigned to Ouranopithecus macedoniensis. The described upper central incisors are separated in two size-groups which in general have similar morphology except for some minor differences such as the presence of a pronounced mesial lingual pillar in the small-sized specimens. The observed significant size difference among the studied incisors is attributed to the strong sexual dimorphism of Ouranopithecus, which is also well expressed in the other teeth. The lingual morphology of the upper incisors of Ouranopithecus are not identical to those of extant great apes, though they have some similarities with those of the African great apes (Gorilla and Pan), while they are clearly different from those of the Asian great ape (Pongo). Even though they have some morphological similarities, the O. macedoniensis central incisors are probably not identical to those of the Eurasian Miocene hominoids; the most similar central incisor is that of Ouranopithecus turkae. Among the known African Miocene hominoids, Nakalipithecus upper central incisor is quite similar in morphology and size to that of Ouranopithecus.