MORPHOMETRICS, HOMOLOGY, AND PHYLOGENETICS - QUANTIFIED CHARACTERS ASSYNAPOMORPHIES

It has been claimed that quantified features are inappropriate for phy logenetic analysis. We consider that claim to be true under most condi tions for characters discovered by commonly used morphometric methods, including outline-based and conventional multivariate methods. The mo st important reason these characters are unsuitable is that one of the tests of homology, the test of similarity, may be difficult to apply to them. This test is not even possible if the methods for comparing f orms, such as outline-based techniques, do not ensure that the charact ers are located in the same part of the anatomy. Conventional methods, including principal components analysis, have no explicit basis for l ocalizing characters. In addition, unless the transformation between f orms is homogeneous, conventional methods cannot dissect transformatio ns region by region to discover characters. However, one morphometric method, the thin-plate spline decomposed by its partial warps (TPS) fi nds characters that can be subjected to the same tests of homology (co njunction, similarity, and congruence) that we would apply to all othe r characters. Among available methods, TPS is unique in being able to locate the center and spatial extent of regional differences in shape and ensures that the same regions are compared among forms. We provide an example using the teleost fishes piranhas, in which tests of homol ogy are applied to a synapomorphy found by the method.