Topology-Based Three-Dimensional Reconstruction of Delicate Skeletal Fossil Remains and the Quantification of Their Taphonomic Deformation

Abstract

Taphonomic and diagenetic processes inevitably distort the original skeletal morphology of fossil vertebrate remains. Key aspects of palaeobiological datasets may be directly impacted by such morphological deformation, such as taxonomic diagnoses and phylogenetic hypotheses, interpretations of the shape and orientation of anatomical structures, and assessments of interspecific and intraspecific variation. In order to overcome these ubiquitous challenges we present a novel reconstruction workflow combining retopology and retrodeformation, allowing the original morphology of both symmetrically and asymmetrically damaged areas of fossils to be reconstructed. As case studies, we present idealised three-dimensional reconstructions of the sternum of the crownward stem-bird Ichthyornis dispar, and cervical vertebrae of the diplodocid sauropod Galeamopus pabsti. Multiple Ichthyornis sterna were combined into a single, idealised composite representation through superimposition and alignment of retopologised models, and this composite was subsequently retrodeformed. The Galeamopus vertebrae were individually retrodeformed and symmetrised. Our workflow enabled us to quantify deformation of individual specimens with respect to our reconstructions, and to characterise global and local taphonomic deformation. Our workflow can be integrated with geometric morphometric approaches to enable quantitative morphological comparisons among multiple specimens, as well as quantitative interpolation of “mediotypes” of serially homologous elements such as missing vertebrae, haemal arches, or ribs.

A toolbox for the retrodeformation and muscle reconstruction of fossil specimens in Blender

“…ribs, limbs). Similarly, methods to quantify deformation and characterize local and global deformation [ 42 ] improve the accuracy of retrodeformation by better understanding how specimens have been altered, as can explorations of the range and modes of taphonomic variation within species represented by frequent fossil specimens [ 43 ]. Figuring the extent of retrodeformation as tension maps of mesh distortions [ 5 ] or maps coloured by relative mesh distance between pre- and postretrodeformed conditions [ 44 ] present options for method documentation.…”

“…These approaches present an effective way to correct plastic deformation—a similar manual method in Blender might be using a Lattice modifier to correct a morphology, and Python script could be used to write more automated land-mark based retrodeformation algorithms in Blender. Nevertheless, combinations of fracturing, displacement, and both brittle and plastic deformation in specimens preclude fully automated approaches [ 42 ]. The diverse modes of damage and deformation present across fossil specimens and the importance of biomechanical data from complex multielement structures such as crania make the adaptability of Blender’s manual tools highly relevant and powerful.…”

“…ribs, limbs). Similarly, methods to quantify deformation and characterize local and global deformation [42] improve the accuracy of retrodeformation by better understanding how specimens have been altered, as can explorations of the range and modes of taphonomic variation within species represented by frequent royalsocietypublishing.org/journal/rsos R. Soc. Open Sci.…”

“…More automated approaches to retrodeformation have used landmarks to warp morphologies to a desired symmetry or form [32,34,42,[44][45][46][47]. These approaches present an effective way to correct plastic deformation-a similar manual method in Blender might be using a Lattice modifier to correct a morphology, and Python script could be used to write more automated land-mark based retrodeformation algorithms in Blender.…”

Forty new specimens of Ichthyornis provide unprecedented insight into the postcranial morphology of crownward stem group birds

“…Measurements of the sternum from the most complete specimens are provided in Table 3 . The three new specimens were previously used as a case study for a new reconstruction workflow combining retrodeformation and retopology, which produced a complete three-dimensional reconstruction of the sternum of Ichthyornis ( Demuth et al, 2022 ), yet they have not been formally described before.…”