新世界ザルにおける下顎大臼歯から推測する上顎大臼歯の形態‐ｗｅａｒ ｆａｃｅｔ８とｈｙｐｏｃｏｎｅの関係について‐

Abstract

The upper molars carry a good amount of information for identifying the fossil Platyrrhines, whereas the lower molars do not. However, the upper molars are not found so much as the lower molars. It is supposed that the occlusal feature of an upper molar is inferred from the occlusal morphology of the respective lower molar. It is hypothesized that wear facet 8 is indicative of the hypocone, as it is formed in the distal part of entocristid of a lower molar by the occlusion with hypocone which is important trait classifying Callitrichine from other Platyrrhines. However, the development of lingual cingulum may give confounding effect on the development of facet 8. In this study, using specimens of Saimiri (hypocone present), Callithrix (hypocone absent) and Saguinus(hypocone partially present), which had different degree of occlusal wearing, I observed both of the upper and lower first molars for the presence both of the wear facet 8 and hypocone under binocular microscopes. As a result, the formation of lower facet 8 was found to be strictly indicative of the hypocone without being influenced by the lingual cingulum. Application of this relationship on such Platyrrhine fossils as Aotus dindensis, Mohanamico hershkovitzi, Patasola magdalena, Xenothrix mcgregori, Nuciruptor rubricae, whose upper molars were not found, and therefore, which have not been properly classified, gave phylogenetic implications.