A new three-dimensional geometric morphometrics analysis of the Ouranopithecus macedoniensis cranium (Late Miocene, Central Macedonia, Greece).

Abstract

This study aims to virtually reconstruct the deformed face (XIR-1) and maxilla (RPl-128) of the Late Miocene hominoid Ouranopithecus macedoniensis from Greece, through the application of mirror-imaging and segmentation. Additionally, analysis was conducted through 3D geometric morphometrics, utilizing a comparative sample of fossil hominoids, extant great apes (Gorilla, Pan, and Pongo) and humans, so as to explore shape variation and phenetic similarities between them. High-resolution computed tomography was used to create digital representations of the XIR-1 and RPl-128 specimens. The virtual reconstruction of the XIR-1 cranium was achieved by mirror-imaging, while the RPl-128 maxilla was virtually segmented and reattached in a correct anatomical position. Anatomical landmarks were registered in three dimensions on a comparative sample of adult crania of extant great apes, humans and fossil hominoids. The data were processed with Procrustes superimposition and analyzed using multivariate statistics methods. Results show that Ouranopithecus macedoniensis falls within or close to the Gorilla convex hull in the principal component analyses, and it is closer to the mean Procrustes shape distance of primarily Gorilla. Both specimens, XIR-1 and RPl-128, are classified as Gorilla based on discriminant function analyses. The results of our geometric morphometrics analyses indicate that Ouranopithecus macedoniensis is morphologically more similar to Gorilla than to Homo, Pan, or Pongo, results that can contribute to the evaluation of existing hypotheses about its phylogenetic position.