Ossicular homologies, systematics, and phylogenetic implications of certain North American Carboniferous asteroids (Echinodermata)

Abstract

Emphereaster missouriensis new genus and species, Ambigaster, new genus, and Delicaster, new genus are assigned to the Carboniferous asteroid family Neopalaeasteridae Schuchert. The neopalaeasterids are similar to but separable from the Carboniferous Monasteridae, Calliasterellidae, and Fandasteridae, n. fam., in ambulacral and other characters. The several families indicate that late Paleozoic asteroids were diverse although poorly documented.Similarities between late Paleozoic stem-group and post-Paleozoic crown-group asteroids allow argumentation on ossicular homologies. In species with only a single row of arm marginals, an earlier suggestion that certain disk ossicles are superomarginals is rejected. Enlarged proximal adambulacrals fill space on the actinal surface whereas actinal ossicles, generally lacking in Paleozoic asteroids, provide the space-filling service in crown-group asteroids.The body wall beyond the ambulacral column and accessory ossicles traditionally have been stressed in the classification of asteroids of all ages. Because of body wall homoplasies, many older taxonomic concepts do not identify monophyletic late Paleozoic clades, nor do they indicate the derivation of the crown group. Ambulacral characters in contrast are conservative through long periods of geologic time, improving phylogenetic resolution as more taxonomic data become available. Now-available ambulacral skeletal data for certain Carboniferous genera suggest membership in lineages basal to the post-Paleozoic crown group.Emphereaster missouriensis and most neopalaeasterids are stoutly constructed suggesting a defensive mechanism against durophagous chondrichthyan fish that co-occur with the holotype of Emphereaster. Abundant sponge spicules within the disk of the holotype suggest it fed on sponges, a prey type widely exploited by living asteroids.