Adding more (semi)landmarks inevitably increases the spatial resolution and 
thus allows one to capture finer anatomical details - whether relevant to 
the biological question or not. This can be advantageous for the 
reconstruction of shapes, especially when producing 3D morphs by warping 
dense surface representations. Basic developmental or evolutionary trends, 
group structures, etc., often are visible in an ordination analysis with a 
smaller set of relevant landmarks; finer anatomical resolution not 
necessarily affects these patterns. However, adding more landmarks cannot 
reduce or even remove any signals that were found with less landmarks, but 
it can make ordination analyses and the interpretation distances and angles 
in shape space more challenging.

An excess of variables (landmarks) over specimens does NOT pose problems to 
statistical methods such as the computation of mean shapes and Procrustes 
distances, PCA, PLS, and the multivariate regression of shape coordinates 
on some independent variable (shape regression). These methods are based on 
averages or regressions computed for each variable separately, or on the 
decomposition of a covariance matrix. 

Other techniques, including Mahalanobis distance, DFA, CVA, CCA, and 
relative eigenanalysis require the inversions of a full-rank covariance 
matrix, which implies an access of specimens over variables. The same 
applies to many multivariate parametric test statistics, such as 
Hotelling's T2, Wilks' Lambda, etc. But shape coordinates are NEVER of full 
rank and thus can never be subjected to any of these methods without prior 
variable reduction. In fact, reliable results can only be obtained if there 
are manifold more specimens than variables, which usually requires variable 
reduction by PCA, PLS or other techniques, or the regularization of 
covariance matrices (which is more common in the bioinformatic community).

For these reasons, I do not see any disadvantage of measuring a large 
number of landmarks, except for a waste of time perhaps. If life time is an 
issue, one can optimize landmark schemes as suggested by Jim or Aki.



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