Upper Cambrian (Paibian, Steptoean) trilobites from the Shallow Bay Formation, western Newfoundland

Abstract Shelf-edge-derived boulders in debris-flow conglomerates of the Shallow Bay Formation of western Newfoundland are relicts of a Cambrian–Lower Ordovician margin of Laurentia that was largely obliterated during the Taconic Orogeny. As such, they are an important archive of trilobite faunas from the edge of the continent. In this paper, we document Cambrian trilobites from the mid-Steptoean Stage (upper Paibian of global nomenclature) in the Downes Point Member. Most of the species are from three boulders assigned to the agnostid Acmarhachis kindlei Fauna and include Dunderbergia Walcott, 1924, Pterocephalops Rasetti, 1944, Quebecaspis Rasetti, 1944, Bathyholcus Rasetti, 1961, Glyptometopsis Rasetti, 1961, and Tholifrons Palmer, 1968. These trilobites are assigned to a new biostratigraphical unit, the Quebecaspis conifrons Fauna, which can also be identified in shelf-margin-derived facies in Quebec, Vermont, and Maryland. Comparison with the shelf interior is more difficult because of ecological and biogeographical differences, but the Q. conifrons Fauna most likely correlates into the Dunderbergia Zone of the traditional Laurentian trilobite zonation. New species are Bathyholcus punctatus , Bellaspidella crocalae , Dunderbergia astropletha , D. bovicephala , D. magnatubercula , “ Eugonocare ” arquatum , Glyptometopsis parilimba , Onchopeltis anconis , and Tholifrons maritima . UUID: http://zoobank.org/9c381131-a457-45d1-bbab-1b839c6b2812