NEW AND OLD LOWER CARBONIFEROUS ASTEROID (ECHINODERMATA) GENERA AND THE SOURCES OF POST-PALEOZOIC CROWN-GROUP ASTEROIDS

Late Paleozoic asteroids (Echinodermata) are poorly represented in museum collections, and their significance is incompletely understood, yet their history bears on origins of modern-type asteroids during the Mesozoic. Most frequently encountered late Paleozoic asteroids include such genera as Monaster and Neopalaeaster , which exhibit comparatively long, slender arms, a small disk, and a peculiar circumdorsal ring of enlarged ossicles. A number of species of Monaster have been recognized from Australia, and a similar but undescribed genus occurs in the Lower Carboniferous of Missouri. Although differing from described taxa largely in technical traits, the new monasterid, along with other Carboniferous genera, shed light on the origins of post-Paleozoic asteroids.

The phylogeny of asteroids has been problematic in part because of taphonomic vulnerability and in part because of evolutionary convergence. Taxonomic interpretation traditionally has emphasized surficial arrangement of both primary and accessory (e.g. spines) ossicles. The ambulacral column, although generally little stressed, provides important added characters.

A new cladistic analysis employing a somasteroid outgroup and treating asteroid genera that range from Ordovician through to the Triassic first occurrence of a surviving family supports separation of asteroid history into three faunas. The first fauna ranges from apparent Ordovician origins through the Late Devonian extinction event, which apparently strongly affected asteroids. The second fauna includes inferred basal representatives of the crown group, which can be recognized using three characters (or character complexes) of the ambulacral column. The incompletely understood complex morphology of the monasterids and that of other late Paleozoic genera help to refine understanding of events that led to the separation of the crown group.

Known diversity of late Paleozoic asteroids does not appear to match that of the earlier Paleozoic; however, much diversity probably never entered the fossil record. Varied late Paleozoic taxa suggest varied feeding habits during this interval.