Reassessment of Dolichopithecus (Kanagawapithecus) leptopostorbitalis, a colobine monkey from the Late Pliocene of Japan

Abstract

In the original description of Dolichopithecus (Kanagawapithecus) leptopostorbitalis, Iwamoto, Hasegawa and Koizumi, 2005, a moderately large-sized colobine monkey from the Late Pliocene of central Japan, affinities to the European Dolichopithecus rather than to the Transbaikalian Parapresbytis were noted based on the similarities in cranial morphology. Computed tomography scans confirm the presence of the maxillary sinus in the holotype, whereas it is probably absent in specimens of the European Dolichopithecus ruscinensis, the type species of this genus. This feature is either present or absent homogeneously in any given genus of living anthropoids. Its presence or absence is unknown in Parapresbytis, but the distinct morphology of the maxillary incisors in this taxon suggests that this form had different feeding habits from the Japanese colobines. These findings suggest that the Japanese colobine should be referred to henceforth as Kanagawapithecus leptopostorbitalis. Kanagawapithecus shares many important facial and dental features with Dolichopithecus rather than with Parapresbytis, but this association depends largely on the limited availability of comparable materials for the latter. Among colobines, the presence of the maxillary sinus is recorded only in Libypithecus and Cercopithecoides. The maxillary sinus is absent in all modern Asian colobines, implying that Kanagawapithecus is an isolated form without any relationship to living forms. Nevertheless, such phylogenetic interpretations are largely dependent on the restricted fossil evidence from the Pliocene and Pleistocene of eastern Eurasia and will be reexamined when new findings are made.