394 Toward a History of the Paleozoic Asteroidea (Echinodermata)

Toward a History of the Paleozoic Asteroidea (Echinodermata) - BAP #394 Existing taxonomic and evolutionary interpretations of stem-group (Paleozoic) Asteroidea differ significantly. Molecular methodologies are unavailable, and because of a fossil record consisting largely of incomplete specimens, comprehensive morphology-based phylogenetic treatments yield equivocal results. Because of axial ossicular vaulting to form the ambulacral furrow, exposure of axial and the adjacent adaxial ossicles is limited in both ancient and modern asteroids and, as a result, taxonomic focus traditionally has been extraxial. Interpretation largely separating the less varied axial adaxial elements from the more varied extraxial offers a fresh approach; here, primacy is axial-adaxial. Evolution of the Asteroidea from the Somasteroidea accentuated two adaptive sequences: The axial or ambulacral skeleton was vaulted to form the furrow, and the adaxial virgal series was reduced to a single adambulacral ossic