GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 194-13
Presentation Time: 9:00 AM-6:30 PM


AUSICH, William I., School of Earth Sciences, Ohio State University, 155 S Oval Mall, Columbus, OH 43210-1398, THOMPSON, Jeffrey R., Department of Genetics, Evolution and Environment (GEE), University College London, Darwin Building, Gower Street, London, UK, WC1E 6BT, RAHMAN, Imran A., Oxford University Museum of Natural History, Oxford University, Oxford, OX1 3PW, United Kingdom, MARTIN, Markus, 371 Pawling Street, Watertown, NY 13601 and COURNOYER, Mario, Museum of Paleontology and Evolution, 541 Congregation Street, Montreal, QC H3k 2J1, Canada

A possible ophiocistioid echinoderm is reported from Telychian (Llandovery, Silurian) strata (Cybèle Member, Jupiter Formation) of Anticosti Island, Québec, Canada. This fossil is preserved along the concave, inner surface of an orthocone cephalopod mold. It consists of a subcircular disc with a large eccentric pore and ten partial or complete, narrow appendages. The central disc is approximately 4 mm in diameter and the entire organism was as much as 30 mm in diameter. Faint remnants of apparent tessellate plating exist on the central disc and appendages. The style of plating, ten appendages, and a large eccentric pore on the aboral surface rule out clades other than the Ophiocistioidea.

If an ophiocistioid, the aboral surface of the theca is covered with small plates and has an eccentric periproct. It has ten plated tube feet (two per ray) that extend beyond the theca and are visible from an aboral view. Plates on the theca and tube feet meet primarily in triple junctions, which is characteristic for tessellate plating. The generic assignment of this specimen is unresolved at this time, but this putative ophiocistioid shares similarities with some members of the Eucladidae and Sollasinidaea. Anticosti Island strata record both Late Ordovician mass extinctions and the earliest Silurian recovery of benthic shelly faunas. If an ophiocistioid, this is the oldest, post-Late Ordovician extinction ophiocistioid known.