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Diplodocid sauropod vertebrae retrodeformation



From: Ben Creisler
bcreisler@gmail.com

The paper about retrodeformation of sauropod vertebrae is now
available in open access in Palaeontologia Electronica:


Emanuel Tschopp, João Russo, and Gordon Dzemski (2013)
Retrodeformation as a test for the validity of phylogenetic
characters: an example from diplodocid sauropod vertebrae.
Palaeontologia Electronica 16.1.2T: 23 p
http://palaeo-electronica.org/content/2013-technical/352-retrodeformation-and-phylogeny


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.