Late Ordovician channel-dwelling crinoids from southern Ontario, Canada. American Museum novitates ; no. 2665

Abstract

"Rheocrinus aduncus, new genus, and new species, subclass Camerata, and Parisocrinus mulletensis, new species, subclass Inadunata, occurr in a late Ordovician (Richmondian) submarine channel fill in the Georgian Bay Formation. This occurrence greatly extends the stratigraphic ranges of the respective families, Anthacocrinidae and Ampheristocrinidae, thereby providing morphologic and temporal support to proposed evolutionary relationships of the foregoing families with the Rhodocrinitidae and Cyathocrinitidae, respectively. Unusual morphological features of R. aduncus indicate that it could form an inclined, parabolic filtration baffle, as do certain living stalked crinoids. A vertically held, planar baffle is suggested for P. mulletensis. These species are believed to have occupied two distinctive microhabitats defined by feeding level, current energy, and feeding mode. They are presently the oldest known channel-dwelling crinoids, and contain among the oldest three dimensional preserved internal organs"--P. [1].