Virtual anthropology: Forensic applications to cranial skeletal remains from the Spanish Civil War

Biological and forensic anthropologists face limitations while studying skeletal remains altered by taphonomic alterations and perimortem trauma, such as in remains from the Spanish Civil War. However, virtual anthropology techniques can optimize the information inferred from fragmented and deformed remains by generating and restoring three-dimensional bone models. We applied a low-cost 3D modelling methodology based on photogrammetry to develop novel forensic applications of virtual 3D skull reconstruction, assembly, restoration and ancestry estimation. Crania and mandible fragments from five Spanish Civil War victims were reconstructed with high accuracy, and only one cranium could not be assembled due to extensive bone loss. Virtual mirroring successfully restored reconstructed crania, producing 3D models with reduced deformation and perimortem trauma. High correlation between traditional and virtual craniofacial measurements confirmed that 3D models are suitable for forensic applications. Craniometric databases of world-wide and Spanish populations were used to assess the potential of discriminant analysis to estimate population ancestry. Our protocol correctly estimated the continental origin of 86.7 % of 15 crania of known origin, and despite low morphological differentiation within European populations, correctly identified 54.5 % as Spanish and 27.3 % of them with high posterior probabilities. Two restored crania from the Civil War were estimated as Spanish, and one as a non-Spanish European. Results were not conclusive for one cranium and did not confirm previous archeological hypotheses. Overall, our research shows the potential to assess the presence of foreign volunteers in the Spanish Civil War and highlights the added value of 3D-virtual techniques in forensic anthropology.