Olenid-dominated trilobite fauna from the Shallow Bay Formation (Cow Head Group), Cambrian-Ordovician boundary interval, western Newfoundland

摘要

A single boulder (PH 8.14), recovered from unit 8 on the Point of Head, Cow Head Peninsula, Shallow Bay Formation (Cow Head Group), contains a unique olenid-dominated trilobite fauna composed of the following taxa: Boeckaspis geordii n. sp., Leiobienvillia terranovica (Rasetti, 1954), hystricurid n. gen. n. sp., Tulepyge sp. A, Tulepyge sp. B, Tulepyge? sp. C, and Symphysurina sp. The pelturine trilobite aB. geordii dominates the assemblage. Boulder PH 8.14 consists of light grey-brown packstone to grainstone. This is atypical for olenid-dominated faunas, which usually occur in dark laminated limestones and shales. The fauna is likely earliest Ordovician in age, but a latest Cambrian age cannot be entirely ruled out. Regardless, this assemblage is unique in that it is the only known olenid-dominated fauna from Cambrian-Ordovicianaboundary sediments in Laurentia. A phylogenetic analysis of Boeckaspis and other putatively closely related taxa (Westergaardia Raymond, 1924 and Jujuyaspis Kobayashi, 1936) was conducted. The results of the analysis indicate that Westergaardia is not monophyletic and as such it is considered a junior synonym of Boeckaspis herein.