Ordovician proetide trilobite Dimeropyge, with a new species from northwestern Canada

Abstract

Dimeropyge öpik, 1937, is a genus currently composed of at least 14 similar Middle (predominantly) to possibly lowest Upper Ordovician species from Laurentia (13 species) and Baltica (one species). Possible Lower Ordovician specimens have been illustrated by Ross (1951). Dimeropyge clintonensis Shaw, 1968, is redescribed, based upon additional material of mature topotypes. A new species of Dimeropyge, D. speyeri, is proposed for material from the Esbataottine Formation in the Mackenzie Mountains, northwestern Canada, previously described as D. clintonensis. A phylogenetic analysis of 10 of the 14 species of this genus is presented (the other species are less completely known, and are related to the analyzed species in a more traditional manner). Ontogenies from protaspid to holaspid stages are provided for D. clintonensis, D. speyeri, and D. virginiensis Whittington and Evitt, 1954. The larval stages of these species are very similar, supporting the close relationship between species assigned to Dimeropyge.