Uncini and the Anchor-Function Hypothesis: Empirical Tests and Causal Explanations

The anchor-function hypothesis developed by Woodin and Merz (1987) attempts to establish the functional significance of uncini as anchoring devices by the positive correlation of uncinal orientation with tube type. The hypothesis was to also provide an adaptive explanation for the assumed homoplasious occurrence of uncini. Systematic and phylogenetic assumptions, observations, and conclusions associated with the hypothesis are examined in conjunction with what is known of cladistic relationships among ordinal, familial, and generic groups examined by Woodin and Merz. Based on these relationships, no systematic data presently exist to support the view that uncini are homoplasious or were derived via selective processes, especially to fulfill the need of an anchoring mechanism. That a correlation between uncinal orientation and tube type can be found in some monophyletic taxa is not evidence per se for selectionist or adaptationist models given the multitude of historical contingencies to be considered.