MIDDLE CAMBRIAN (DRUMIAN) CORYNEXOCHID TRILOBITES FROM THE COW HEAD GROUP, WESTERN NEWFOUNDLAND

During the Ordovician Taconic Orogeny, the Laurentian margin of the Iapetus Ocean was destroyed, but facies and faunas were preserved in shelf margin derived boulders that accumulated in debris flows on the continental slope. In Newfoundland, these slope successions, which include the Cambrian–Lower Ordovician Cow Head Group, are now part of the Humber Arm terrane, which was emplaced onto the Laurentian shelf during the orogeny. The Cow Head Group provides the most complete record of these “lost” faunas, which include trilobites, agnostoid arthropods, and linguliform brachiopods. Middle Cambrian (Drumian) boulders yield abundant and diverse corynexochid trilobites, including species of Bathyuriscus, Corynexochides, Kootenia, Olenoides and Zacanthoides, that have affinities with other shelf margin derived faunas in Quebec and Alaska. Computer-based phylogenetic analysis of a representative set of species of Family Zacanthoididae supports monophyly of most zacanthoidid genera, although Zacanthopsis is nested within Zacanthoides, and may be a junior synonym of the latter.