Computerized restoration of a fossil cranium based on selective elimination of estimated taphonomic deformation

Objectives Due to taphonomic processes, fossils have often undergone plastic deformation. To correctly assess the morphological affinities of such specimens, the original antemortem shape of the deformed specimens must be reconstructed. Here we describe a method to mathematically isolate and selectively eliminate the taphonomic deformation of a fossil cranium for restoration of its original antemortem appearance, and apply this method to reconstruction of a cranium of Mesopithecus from the late Miocene of Greece. Materials and methods Three-dimensional (3D) models of the fossil cranium and the crania of phylogenetically close extant species were generated, and 3D shape variations of the crania were analyzed based on anatomical and sliding semi-landmarks. Using principal component analysis, we attempt to extract the taphonomic deformation component of the shape variation that is presumably orthogonal to the hyperplane describing interspecific variations of the intact crania of the extant species. Landmarks were repositioned so that the extracted taphonomic component is selectively eliminated. A thin-plate spline was used to describe the 3D transformation from original and repositioned landmarks, and the entire surface of the fossil was restored. Results The proposed method successfully extracted and eliminated the component of the taphonomic deformation and enabled restoration of the original antemortem appearance of the deformed fossil cranium. Discussion Unlike conventional methodologies, the proposed method does not rely on the assumption of symmetry for correction of taphonomic deformation. Although some methodological limitations apply, the proposed method may contribute to improved accuracy, objectivity, and transparency in virtual reconstruction of deformed cranial fossils.