NEW ORDOVICIAN CRINOID LOCALITY AND THE ONTOGENY OF GLYPTOCRINUS DEDACTYLUS

A recently discovered limestone Lagerstätten in Mason, Ohio (presumed to be in the Liberty Formation) includes exceptional preservation of many Ordovician fossils, the most prominent of which are the crinoid taxa Glyptocrinus, Iocrinus and Plicodendrocrinus. The crinoid specimens, which currently number around ninety calices, show full articulation as well as the possible ontogeny of Glyptocrinus dedactylus. The superfamily Glyptocrinacea in the suborder Glyptocrinina are characterized by many fixed brachials, large regular interbrachials, a small amount of brachials within each adult ray, a basal circlet pentagonal and all radials adjoining on calices. In the ontogeny of the superfamily the younger animals lack intersecundi brachials, have closely spaced arms in each ray (as well as being separated by interrays) and have paralleled columned brachials that overtime will “stack” and will become more column-like. Adult stages form intersecundi brachials, and the spacing of the interrays are filled with spreading radiating brachials for growth to function properly.

Fully articulated specimens of Glyptocrinus dedactaylus showing all the stages of ontogeny have until now, not been collected from the same deposit. The fossils needed to view the ontogeny of this species, from “youth” to “adult,” appear to be present here. The two “juvenile” Glyptocrinus specimens show the characteristics that coincide with the description of how a crinoid in this family should begin to form. Upon closer inspection of the specimens, one can view the brachials (which are few in number) and observe interrays in between two paired brachial “couples” all around the specimen’s calyx. This characteristic as well as what appears to be “still-forming” plates around the basal and radial areas shows that these specimens are probably “juvenile” Glyptocrinus. The discovery of this deposit is important because it can elucidate the formation of an Ordovician Lagerstätten, demonstrate the ontogeny of Glyptocrinus and give some clues as to the overall taphonomy of crinoids while they are developing.