Nasal architecture in Procynocephalus wimani (Early Pleistocene, China) and implications for its phyletic relationship with Paradolichopithecus

Abstract

Procynocephalus and Paradolichopithecus are large Eurasian papionins from the Middle Pliocene to Early Pleistocene. The two genera are regarded as being phylogenetically close, but their phyletic position is still disputed, in particular regarding to which subtribe, Papionina or Macacina, they are close to. Many fragile structures of the nasal region are well preserved in the type specimen of Procynocephalus wimani from the Xin’an locality in China. Computed tomography scans showed that the Xin’an specimen has no maxillary sinus, an inferior meatus extending medially from the slightly superior portion of the maxillary body, and a thick maxillary body with no maxillary fossa. Morphological variation in the nasal region was surveyed in extant papionins. Our analysis showed that the maxillary sinus is found even in Papio/Theropithecus and that its formation is confirmed for all Macaca. The inferior conchae are suspended from the superior portion of the nasal cavity in Papio/Theropithecus and Mandrillus, and the maxillary fossa is developed by major absorption of the maxillary cancellous bone in Papionina. These findings indicate that a given fossil specimen having a maxillary sinus does not always belong to the Macacina lineage, and that a given specimen having a thin maxillary body is closer to the Papionina. Despite the paucity of evidence definitive of its phyletic position, these morphological examinations suggest that Procynocephalus is closer to the lineage of Macacina though it lacks the maxillary sinus. Whereas Paradolichopithecus arvernensis and Paradolichopithecus sushkini show some morphological similarities to and differences from each other and Procynocephalus, their nasal architecture is similar to that seen in the Macacina rather than in the Papionina. The morphological evaluations of the nasal region in African forms are expected to contribute to our understanding of the phyletic relationships and adaptive radiation of the large Eurasian papionins in the Plio-Pleistocene.