Taphonomy and Taxonomy of the Early Ordovician Gastropod Ceratopea canadensis (Billings), 1865

Abstract

Several hundred silicified specimens of Pleurotomaria canadensis Billings, 1865 and other rare fossils indicative of a late Canadian age have been collected from the Oxford Formation, southwest of Ottawa, Ontario. Redescription of this neglected gastropod species permits its assignment to the genus Ceratopea. even though no ceratopean opercula have been found.Rare faunal elements include ribeirioids and open coiled gastropods that may have lived, respectively. in and on a mud bottom. There is no evidence that they have been transported. It is suggested that Ceratopea canadensis lived on algal mats some distance away from the shore and from where it is now found. After death, the soft parts of this gastropod decayed and the heavy operculum rotted off. The lightened shell, filled with gas, floated shoreward, likely under conditions of relatively calm water. Discovery of opercula within the Oxford Formation would provide evidence to support this hypothesis.La Formation de Oxford, du sud-ouest d'ottawa, Ontario, a produit plusieurs centaines de spkcimens silicifiks de Pleurotomaria canadensis Billings, 1865 et d'autres fossiles rares indiquant un 2ge Canadien supkrieur. Une nouvelle description de cette espece nkgligke de gastkropode rend possible son attribution au genre Ceratopea, mtme si aucun opercule caractkristique de ce genre n'a kt6 retrouvd.Parmi les dements fauniques plus rares, on trouve des gastkropodes ribeirioi'des et B enroulement lache qui ont pu vivre respectivement, dans et sur un substrat boueux. On ne note aucune kvidence de transport. I1 est suggkrk que Ceratopea canadensis vivait sur des tapis algaires ? i quelque distance du rivage et du lieu ou il est prksentement trouvk. Apres la mort, les parties molles de I'animal se dkomposerent et le lourd opercule s'en dktacha. La coquille, ainsi allkgke, remplie de gaz, a pu flotter vers le rivage, probablement sous des conditions d'eau relativement calme. La dkcouverte d'opercules dans la Formation de Oxford tournerait des kvidences pour ktayer cette hypothese.[Traduit par le journal]

The paleontology of rostroconch mollusks and the early history of the phylum Mollusca

“…R. calcifera is known from several localities in the Beekmantown Group (Lower Ordovician) of Ontario, Canada. Recent work by Yochelson and Copeland (1974) indicates that the beds containing this species are latest Canadian (late Early Ordovician) in age in Ontario. Two specimens from the Tanyard Formation of Texas (lower Lower Ordovician) are herein also assigned to R. calcifera (USNM 127908, 127909); these specimens were previously figured by Cloud and Barnes (1948).…”

Ordovician Gastropoda from Northeast Greenland

“…This species was re-described by Yochelson & Copeland (1974, p. 205), and they noted, "...no close correspondence between the syntypes and the line drawings." Yochelson & Copeland (1974) noted the similarity of C. unguis and C. canadensis and suggested that they might be placed in synonymy, although they did not. No operculum has been associated with C. canadensis.…”

“…Several species of Ceratopea occur in western Newfoundland (Rohr et al 2000. Ceratopea normani (Billings, 1865), which is a synonym of C. canadensis Yochelson & Copeland (1974), is known from an internal mold from Billing's (1865) Unit G (Catoche Formation). Shells probably of C. canadensis occur in the Catoche Formation (Rohr et al 2000.…”

“…The growth lines on the operculum do not necessarily reflect the reentrants along the shell aperture, since the operculum was withdrawn inside the aperture (Yochelson & Bridge 1957, Rohr et al 2004b. Yochelson & Copeland (1974) suggested that C. canadensis may be a synonym of C. unguis, but no operculum is associated with it.…”

Lower Ordovician trilobites of the Oxford Formation, eastern Ontario

“…'Fhis is probably the lower siindg: division of the Oxfc~rd Formatic~n according to its recent revision by Bond and Greggs (1976, p. 22 Wilson (1946, p. 17) conclalded that the Oxford Formation is 'early Reekmantown' in age, but more recent age assignn-nents of the gastropod, cephalopod, and conodont suggest a somewhat younger age. Based on the presence of C,'cratopuks ccancrcJensis and other gastropods in the Oxford Formation of 0xfc)rd and Marlborough Townships, Yochelson and Copeland (1974) suggested a late Canadian to latest Canadian age for this form:ition. A similar age was indicated for the cephalopcads (Flower, in Uochelson and Copeland 1974).…”