Two new multiarmed Paleozoic (Mississippian) asteroids (Echinodermata) and some paleobiologic implications

Abstract

Lacertasterias elegans and Schondorfia fungosa are new genera and species of multiarmed asteroids described from the Kinderhookian? (Mississippian) Gilmore City Formation of Iowa and the Chesterian (Mississippian) Haney Formation of Illinois, respectively. Based on ambulacral construction, the former belongs to the Paleozoic asteroid stem group whereas the latter is distinct from but closer to post-Paleozoic asteroids.The multiarmed condition is atypical today; nevertheless, multiarmed species are morphologically varied and taxonomically widely distributed. The condition is considered problematic; it is uncertain whether or not multiarmed organization is adaptively neutral. Although only convergent with rather than ancestral to post-Paleozoic multiarmed asteroids, both new genera share important similarities with modern multiarmed predators, implying a predatory life mode for the fossils. The similarity between phylogenetically disparate Paleozoic and post-Paleozoic asteroids implies the multiarmed condition is beneficial, and benefits endured in spite of the major biotic changes that occurred around the end of the Paleozoic.