LIFE AND DEMISE OF THE PERIECHOCRINIDAE CLADE (CLASS CRINOIDEA)

New Early Carboniferous periechocrinids (monobathrid camerate crinoids) highlight the complex evolutionary history of this clade. The Periechocrinidae (20 genera) persisted from the Early Silurian through the Early Mississippian on Avalonia, Baltica, Laurentia, and Gondwana. Although they lived in a variety of habitats, periechocrinids were most abundant in reef-associated and other carbonate settings. A face-value examination of species and genus richness indicates that, after initial adaptive radiation in Laurentia, periechocrinid success was asynchronous among paleocontinents.

Periechocrinids diversified during the Wenlock on Laurentia, Baltica, and Avalonia. Globally, the Wenlock had an excess of generic and specific origination. The periechocrinid richness high continued into the Ludlow only on Laurentia. They persisted through the Late Silurian and Early Devonian with low richness worldwide (real or sampling). The Devonian radiation began on Laurentia and Gondwana, and each paleocontinent experienced a slight diversification of genera and to a lesser extent species during the Emsian. This included a small generic radiation on Gondwana, and an excess of origination occurred only among genera, i.e. genera had few species. Alternatively, the Laurentian diversity spike was Givetian. On Laurentia, Givetian periechocrinid taxa were short lived, so there was neither an origination nor an extinction excess in either genera or species. Following the Frasnian-Famennian extinction event, periechocrinids had a final minor diversification in carbonate facies during the Early Tournaisian on Laurentia and Avalonia. This diversification had a global signature similar to the Wenlock, i.e. generic and specific origination excess. However, this final radiation was short lived, with the youngest periechocrinids Early Visean. The youngest periechocrinids co-occurred with and were eventually replaced by the dominant Early Carboniferous camerate crinoids, Actinocrinitidae, Batocrinidae, Coelocrinidae, and Platycrinitidae.