Techniques for digital restoration of cranial elements on three-dimensional surface models

Abstract

Digital restoration is the process by which preservational or other types of damage are removed to recover the putative original morphology of fossil specimens. In the present work, three-dimensional (3D) surface models of skulls and mandibles of 32 cynognathians (Synapsida, Cynodontia) specimens from South America were digitally restored. The main restoration techniques used come from the literature and are adapted to the particular preservational problem. A classification into three restoration grades (low, medium and high) is proposed, taking into account the number of techniques used and the percentage of damage of the fossil. The higher the degree ofdamage, the greater the complexity of the restoration and the higher the level of interpretationadded. Of all the specimens, 36.5% presented a low grade of restoration, 15% presented a medium grade, and 7.3% a high grade. Among the major damages recorded in the cynognathians specimens the following stand out: partial or total fragmentation of one of the zygomatic arches, total loss of the postdentary bones, fragmentation of the coronoid processes, and lithostatic deformation. The unidirectional deformation could not be completely eliminated in the fossils that presented it, beingthe only unresolved restorative problem. Detailing and documenting the totality of the restorative procedures allows establishing a traceability of the changes applied to the specimens, being extremely useful for researchers confronted with similar problems.