Validity and composition of the Silurian trilobite genera Borealarges and Dicranogmus, with new species from the Canadian Arctic

Abstract

New silicified material from Arctic Canada demonstrates that the lichid trilobite genera Borealarges and Dicranogmus, recently claimed to be synonyms, are independent groups with no close phylogenetic connection to one another. Dicranogmus has been known mainly from cranidia alone; prior association of librigenae and pygidia with the Arctic Canadian species D. skinneri has been queried. This association is correct beyond reasonable doubt, based on description of new material of both D. skinneri and a new species. Three new species of Borealarges are related to B. tuckerae Adrain 1994. Cladistic analysis supports the monophyly of this species group. Pending further new information, however, the group is retained within the genus Borealarges. The stratigraphic range of the species group is extended from the lower Wenlock (Sheinwoodian) to upper Ludlow (Ludfordian) by the discovery of a rare species in the Douro Formation of Cornwallis Island, Arctic Canada. New taxa from the Wenlock of the Cape Phillips Formation, Arctic Canada, include Dicranogmus wynni, Borealarges nicoae, B. warholi, and B. yulei.