INVESTIGATING COVARIATION BETWEEN MORPHOLOGICAL, ECOLOGICAL, AND TAXONOMIC DIVERSITY OVER THE EVOLUTIONARY HISTORY OF DIPLOBATHRID CRINOIDS

Disparity, the morphological diversity of biological forms, is a fundamental component of diversity that can be used to identify macroevolutionary patterns and processes through time. Disparity analyses are most frequently conducted using cladistic-type character matrices. However, integrating morphological matrices with those that reflect functional ecology permits investigation of a suite of new questions relating to evolutionary phenomena such as adaptive radiations, ecological or morphological convergence, and community complexity.

Here, we use a phylogenetic framework to investigate the interplay between morphological disparity, functional ecology, and taxonomic diversity over the ~150-million-year history of the crinoid order Diplobathrida. We use a high-resolution dataset that includes 123 morphological characters, 28 ecological characters, and more than 200 species. In addition to traditional methods, dissimilarity among taxa was estimated using a recently proposed modification to common metrics (Gower’s coefficient, Wills’ GED) that treats inapplicable characters separately from missing data. Preliminary genus-level analyses indicate total occupation of morphospace and functional ecospace are tightly correlated throughout diplobathrid evolutionary history. These fluctuations in total ecological and morphological diversity are broadly paralleled by tree-based estimates of taxonomic diversity through time. Although total morphospace and ecospace occupation decreased steadily through the late Devonian–Mississippian, a notable decoupling between ecological and morphological diversity occurred during the Mississippian, when an entirely new area of morphospace was explored. This shift in morphology was accompanied by an increase in the number of species within remaining genera but with no ecological innovation. This suggests convergence on previously explored ecological niches through new morphological pathways, as well as ecological restriction in diplobathrid crinoids near the end of their evolutionary history.