Introduction

The wide range of morphologies seen among taxa, as well as intraspecific variability, when combined with the diversity of information carried by morphology, ensures that no “one size fits all” method exists for morphologic characterization. In some cases, interest resides in determining how a single species' form has changed in response to environmental parameters; the organism being used solely as a proxy indicator. In other cases, shape components linked to such environmental factors will be excluded in order to determine the nature and rates of change of the genome as reflected in morphology. In still other cases, the morphology may be of interest in terms of some sort of functional efficiency with respect to locomotion or musculature.

A task of the investigator is to choose the best procedure for the particular experimental situation. Paramount in any investigation is choosing the optimum method to define statistically significant morphological changes. Forms that depart from classic Euclidean (geometric) regularity commonly can generate a large number of numeric descriptors. Usually, for any given research objective, only a subset of such variables are applicable. Relevant descriptors are termed “features,” and feature selection is a critical first step in any morphological analysis. Features may be known a priori on the basis of prior research on the taxon or by analogy with related taxa.