A PHYLOGENY OF PALEOZOIC OPHIUROIDEA (ECHINODERMATA)

Ophiuroids are common members of Paleozoic communities, although total number of specimens remains low, probably due to taphonomic biases. 160 Paleozoic species and 61 genera are recognized here, although ophiuroid systematics are in need of significant revision. Paleozoic ophiuroids as a group have not been the subject of modern cladistic analysis, although both post-Paleozoic, and more recently, Ordovician ophiuroids have received detailed study. A more complete Paleozoic hypothesis is needed to test existing work and look for connections between Paleozoic and post-Paleozoic faunas. Here, all reasonably well known and well preserved Paleozoic genera are considered.

The present hypothesis is based on a cladistic analysis of 34 genera and 57 morphological characters. The stelleroid genus Pradesura (Arenig) was chosen as the outgroup. Analysis resulted in 14 shortest trees; polytomies are restricted to higher nodes. Traditional families including the Protasteridae, Encrinasteridae, Cheiropterasteridae, and Klasmuridae are readily recognizable; however, separation of the Furcasteridae and the Eospondylidae, as well as the Ophiurinidae and the Ophiuridae, are not supported. The traditional Zeugophiurina is polyphyletic. The suggested use of the protasterid Strataster as outgroup for analysis of post-Paleozoic members is not supported.

Paired ambulacrals appeared at least twice. Dorsal arm plating, reported in several protasterid ophiuroids, is only analagous with dorsal arm ossicles developed in the crown group. Ventral arm ossicles appeared only in the Ophiurida. Ophiuroid mouth frame morphology was relatively conservative although this is difficult to evaluate because of taphonomic alterations.

Mapping of stratigraphic data onto the phylogenetic hypothesis suggests a gap in the fossil record, especially for the klasmurids and the group that includes the ophiurinids and ophiurids, members of which first appeared in the Lower Devonian. The latter includes modern taxa, yet a basal position on the cladogram indicates an early Paleozoic emergence. All remaining Paleozoic clades became extinct before the Triassic, hence most known Paleozoic groups played no part in the post-Paleozoic diversification.