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Re: Diplodocid sauropod vertebrae retrodeformation

Robert Bakker was doing something similar many years ago, making wax casts of 
diplodocid skull 
bones and manipulating the parts by hand to try to undo taphonomic deformation. 
It sounded like a 
very subjective method though.


On Tue, Jan 29th, 2013 at 9:19 AM, Ben Creisler <bcreisler@gmail.com> wrote:

> 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.


Dann Pigdon
Spatial Data Analyst               Australian Dinosaurs
Melbourne, Australia               http://home.alphalink.com.au/~dannj