Wednesday, November 4, 2009

Dental eruption sequence of a fossil 'baboon' (Paradolichopithecus arvernensis)

The fossil remains of this large-sized 'baboon' found at Vatera, Lesvos, Greece (Plio-Pleistocene boundary, or Late Pleistocene now that the boundary has been moved up again) includes a mandible of a young male with unerupted wisdom molar. We X-rayed the specimen to reveal the unerupted elements and the mineralization of their crowns. The chronological, or individual age of our Paradolichopithecus at the time of its untimely death is estimated at between 5.0 and 5.3 years of age, based on eruption patterns and root formation times of similar-sized living papionins. Mandrills, yellow baboons and Japanese monkeys are in their puberty at this age and stage of dental development, from which we conclude that our male was in his puberty as well. During this period, young males disperse from their natal groups and live at the periphery of their troupes. Risks of predation, disease, and injury are higher than before; a quarter of male mandrills dies before reaching adulthood. Among known Paradolichopithecus specimens, nearly half have died before the third molars erupted. This may be explained either by some taphonomic factor or due to higher mortality levels during puberty.
We further found that the eruption sequence of the permanent mandibular dentition of this male is {m1 i1–2 m2} p4, p3, c, m3. The order of the already fully erupted elements (between curly brackets) is based on data from the living baboons, mandrills, macaques and geladas. The p4 p3 sequence as seen in our Paradolichopithecus occurs at high frequency is other papionins as well: Macaca nemestrina, M. mulatta, Mandrillus sphinx, Papio cynocephalus, but not in Papio anubis, Macaca fuscata and M. fascicularis. Theearlier root formation of p4 seems thus not to be related with body size or phylogeny. There is a considerable delay in the canine development relative to the premolars, as in other papioninmales; the m3 is delayed in formation relative to the premolars and the canine. In total, the dental eruption sequence of Paradolichopithecus is very similar to that of the living papionins.

Read more in Van der Geer, A.A.E., Dermitzakis, M. 2008. Dental eruption sequence in the Pliocene Papionini Paradolichopithecus arvernensis (Mammalia: Primates) from Greece. Journal of Vertebrate Paleontology 28 (4): 1238-1244. (Ask a pfd,