<Emphasis Type="Italic">Compsaster formosus</Emphasis><Emphasis Type="SmallCaps">Worthen &; Miller</Emphasis> (Asteroidea; Echinodermata): A Carboniferous homeomorph of the post-Paleozoic Asteriidae

All adequately known post-Paleozoic asteroids are either assignable to surviving families or closely related families whereas no Paleozoic species assignable to a surviving order has been recognized. The Mississippian speciesCompsaster formosus is similar enough to various Recent taxa in overall form as well as in the form and arrangement of body wall ossicles to raise the issue of affinities: IsC. formosus nested within a phylogenetic branch hitherto known only from post-Paleozoic strata or is it only homeomorphic?The nature of the ambulacral system is critical to interpretation of echinoderms, and post-Paleozoic asteroids share three fundamental ambulacral characters or character suites: dorsal podial pores, staggered positioning of ambulacrals and adambulacrals, and complex articular structures between these two ossicular types.Calliasterella americana, a Carboniferous asteroid, shares the three ambulacral features, although it is distinctive from post-Paleozoic asteroids in other ways.Compsaster formosus exhibits at least two of the three ambulacral characters, although presence of staggering has not been finally established. LikeC. americana, C. formosus differs from post-Paleozoic species in details of ambulacral anatomy as well as aspects of ventral body surface ossicular arrangement. Although approaching crown-group organization,C. formosus nevertheless represents a branch basal to the crown group.Because asteroids are generalists, understanding of life habits ofCompsaster is sketchy in spite of morphological similarities between it and younger genera.Compsaster probably was epifaunal and its overall form is strongly reminiscent of that of Recent predatory asteriids but it is also similar to small-particle feeding echinasterids.