Idealized landmark-based geometric reconstructions of poorly preserved fossil material: A case study of an early tetrapod vertebra

Abstract

Three-dimensional (3D) digital models of bone morphology are used frequently in paleontology and anthropology. Because fossils are often fragmentary or distorted, it often becomes necessary, for either aesthetic or practical reasons, to create an idealized version of digital skeletons. We propose a method for building landmark-based geometric reconstructions of fossil bones in 3D graphics software using CT or laser scan data as a template. This method does not require specialized software or artistic expertise. It allows control of local mesh density, specification of important landmarks and major planes, elimination of large holes and extraneous structures, and interactive adjustment of 3D shape by moving a small number of vertices to correct minor taphonomic deformation. The result is a simple, illustrative, and accurate model that can be used for diverse analytical and visualization applications, including reconstructions of incomplete fossils, watertight models for mass and center of mass approximation, base meshes for thin plate spline warping, and intermediates in an incomplete series via "morphing." To demonstrate the method, we applied it to reconstruct a dorsal vertebra from the basal tetrapod Acanthostega gunnari. We validated our methodology with linear and geometric morphometric comparisons of our reconstructions both against the original scan data and between three different operators. Based upon four linear measurements, the average deviation of the models from the original was minimal, showing that the method preserves the proportions of the original fossil. We found no statistically significant shape difference between models built by different operators, demonstrating that the method is repeatable. © Palaeontological Association February 2012.