Comparative analysis of outer and inner skull morphology between Paradolichopithecus/Procynocephalus and Cercopithecines

Περίληψη

Procynocephalus/Paradolichopithecus aff. arvernensis, DFN3-150, is a large cercopithecine monkey discovered from the Early Pleistocene of Dafnero, northwestern Greece. The external and internal cranial morphology was analyzed and compared to 24 specimens of modern Cercopithecinae from the genus of Papio and Macaca in order to evaluate the most closely related phylogenetic group. Using computed tomography CT and high-resolution micro-computed tomography microCT, 32 metrical measurements of the external features for each cranium were made. For the inner structure the presence, size and also shape of the maxillary sinuses were studied. Maxillary sinuses (MS) are paranasal sinuses that develop postnatally and invade the cancellous bone of the maxilla. It is hypothesized that the presence of maxillary sinus was lost in a common ancestor of the extant cercopithecoids and reoccurs in the lineage of Macaca in Cercopithecinae. All the data were standardized by dividing each measurements by its median (for the external) and the geometric mean (for inner) to exclude the shape differences correlated with size. DFN3-150 has a baboon-like appearance, more closely related with the Papio lineage as far as its external cranium features but it has maxillary sinuses which are typical for macaques. However, the presence of maxillary sinuses is not considered of high phylogenetic value since there are Papio and Theropithecus specimens that show pneumatization of the maxilla and in some cases maxillary sinuses. The size of MS showed a wide range in the Macaca specimens of the study, making it also a dubious characteristic. One new method of studying MS could be the size of the nasal cavity, relative to the MS, and the shape of the MS alongside their length, yet further investigation is needed. In addition, the affinities of the three studied genera were tested with cladograms using Wagner’s and Dollo’s optimality criteria, suggesting that Procynochephalus/ Paradolichopithecus is a macaca-like baboon. To support this new hypothesis further work needs to be done based on the evolvability of the craniofacial complex as well as morphometric comparisons with craniums of the later Neogene Papionini and early extinct species of P. izodi, P. angusticeps and Parapapio.