ISSUES IN TAXONOMIC SCALING FOR MULTIFACETED MORPHOLOGICAL STUDIES: EXPLORING THE EVOLUTIONARY HISTORY OF ECHINODERMS

Combining taxonomic diversity, morphological disparity, and phylogenetic relationships is a powerful tool in deciphering evolutionary dynamics within a clade. When this diverse information is further combined with time we can address hypotheses of tempo and evolutionary rate during pivotal intervals, such as the origin of a clade, environmental shifts, or ecological perturbations. The addition of biogeographic information can assist in the testing of evolutionary mechanism and processes underlying the observed patterns. The broad and extensive synthesis of information provides an opportunity to decipher evolution through a multifaceted approach.

The obvious difficulty with this methodology is the extensive data needed for its implementation. In particular, the amount of time and effort increase exponentially at higher taxonomic levels, which results in few studies exploring the detailed evolutionary dynamics at the origin of the major phylum. Echinoderms are a good example of the opportunities and difficulties in undertaking this extensive approach in the study of macroevolution. Echinoderms in the early Paleozoic diversified to fill multiple ecological niches, which resulted in the evolution of many distinctive and novel body plans. Over 20 classes have been proposed for Early Paleozoic echinoderms. Anatomical descriptions were mostly done independently for these classes, resulting in muddled and inconsistent anatomical terminology that makes the construction of morphological databases difficult. In addition, there are unique challenges in constructing morphological and cladistics datasets. Often there have not been broad phylogenetic analyses done at the phylum level, which is paired with disagreements in homology schemes. Ideally, datasets capturing disparity will include proposed homologous structures as well as autapomorphies, and structures that are evolutionarily plastic (environmentally or ecologically). This will remove the burden of recognizing homology, but requires detailed anatomical study of a broad expanse of animals. Preliminarily results of the compilation of these diverse dataset in echinoderms shows the complicated paths of evolution and rapid expansion in morphological diversity echinoderms transversed during the Early Paleozoic.