Retrodeformation as a test for the validity of phylogenetic characters: An example from diplodocid sauropod vertebrae

Abstract

Tectonic strain is ubiquitous in rock formations, leading to deformations, faults, and cracks at small as well as large scales. Fossils embedded in these strata will passively participate in these deformations, and have rarely been found undistorted. This affects ratios used in phylogenetic analyses. As a case study, diplodocid (Dinosauria: Sauropoda) cervical vertebrae were subjected to two different methods of retrodeformation, and the same methods were tested with a manually deformed digital model of a Dodo (Raphus cucullatus, Linnaeus, 1758) cervical vertebra. The results indicate that shape changes considerably in all dimensions. The tests showed that generally, retrodeformation restored symmetry, but increased deformation induced by compression. By comparing the trends obtained by the Raphus cucullatus analysis with the results from the diplodocid vertebrae, phylogenetic characters that are more prone to various types of deformations were identified. Phylogenetic analyses without these questionable characters generally yielded better resolution, shorter most parsimonious trees, and higher supporting values. Ratios used for character definitions, as well as other character information possibly affected by deformation, have to be applied very carefully, and highly susceptible ratios should be avoided a priori. As shown in this study, retrodeformation can work as a tool to identify such ratios and characters, but it has to be simultaneously tested with similar bones from extant taxa. © Palaeontological Association January 2013.