Dear Dr. Cardini,
Thanks for always bringing up discussions in the geometric morphometrics community on topics that sometimes seem to be conventional, but that may commonly be misapplied. We agree that in order to infer biological meaning to our results, the methods should be well supported first. I understand that both the Procrustes superimposition and the potential use of a sliding procedure for semi-landmarks result in a possibly problematic (and widely discussed in the literature) high correlation of landmarks. I also understand that this is one reason why analyses in Procrustes shape space should be regarded as whole-shape analyses. However, I would like to constructively bring up a simple possible procedure for the biological interpretation that most biologists are after and would like to know if you agree with this. After having analyzed the whole-shape variation of an anatomical structure, we are able to induce how this anatomical structure varies – this is probably the reason why most researchers use geometric morphometrics. “How this anatomical structure varies” implies that there is a set of landmarks that are varying in the Procrustes shape space. If we want to know if these landmarks are biologically relevant, I believe that what we can do is use the raw coordinates of those landmarks and calculate the linear distances between them (we may do a size correction on these if wanted also), just like linear morphometrics do. We can do this for, for example, identifying anatomical differences between groups of organisms (comparisons of linear distances between groups) or identifying differential variation within a structure. This may sound like I am suggesting to perform linear morphometrics instead of geometric morphometrics. However, the message that I want to get through is that geometric morphometrics can help on understanding how and identifying where the shape of a structure varies and that we can also use linear morphometrics (with our own 2D or 3D coordinates) for providing evidence that the landmark variation observed in the Procrustes shape space is also reflected in the raw real anatomical structure. I hope that this is not off-topic, but I just wanted to bring it up for the people that may be worried about their own conclusions about the biology of their study system. Cheers, Pietro Viacava On Monday, 10 May 2021 at 10:49:21 pm UTC+10 [email protected] wrote: > Dear All, > I have the impression that studies analyzing one landmark at a time > after a Procrustes superimposition (plus a possible sliding of > semilandmarks) are beginning to pop up here and there in the biological > literature. > I wonder whether there's some revolutionary evidence, which was > published and I missed, that contradicts a most basic principle of > Procrustes shape analysis: never to analyze Procrustes shape variables > one at a time, including especially the case of pairs or triplets of > 2D-3D landmark Procrustes shape coordinates. This is nicely summarized > by Paul in J. Anat. (2000) 197, pp. 103–120; exemplified in Fig. 9 of > doi:10.1371/journal.pone.0025630; related to the problem of analyzing > one PW at a time discussed by Jim (Syst. Biol. 47(1):147± 158, 1998); > and most likely known since the early days of Procrustes GMM. > I would be astonished to find that this is not longer true but I am > happy to be surprised. > > Many thanks in advance for refs and feedback. > Please, if you reply directly to me, let me know if I can share your > answer. > > Cheers > > Andrea > > > > > -- > Dr. Andrea Cardini > Researcher, Dipartimento di Scienze Chimiche e Geologiche, Università di > Modena e Reggio Emilia, Via Campi, 103 - 41125 Modena - Italy > tel. 0039 059 4223140 > > Adjunct Associate Professor, Centre for Forensic Anthropology, The > University of Western Australia, 35 Stirling Highway, Crawley WA 6009, > Australia > > E-mail address: [email protected], [email protected] > WEBPAGE: https://sites.google.com/view/alcardini2/ > or https://tinyurl.com/andreacardini > > FREE Yellow BOOK on Geometric Morphometrics: > https://tinyurl.com/yellowmorphobook > > ESTIMATE YOUR GLOBAL FOOTPRINT: > http://www.footprintnetwork.org/en/index.php/GFN/page/calculators/ > SUPPORT: secondwarning.org > -- You received this message because you are subscribed to the Google Groups "Morphmet" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/morphmet2/22d337c5-4013-4931-87ec-0c8edd40bf87n%40googlegroups.com.
