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.

Late Ordovician and Silurian Lichid Trilobites From Northwestern Canada: Eight New Species From Subfamilies Lichinae, Platylichinae, and Trochurinae

“…questioned the assign ment of the pygidium, arguing that the pygidium would be more correctly associated with lichine or tetralichines. Our study using material from the Mackenzie Mountains, as well as other work based on material from the Canadian Arctic and Gotland(Adrain and Ramskold, 1996;Adrain, 2003), confirm the correctness of assigning pygidia of this type to Dicranogmus Thomas and Holloway (1988). andAdrain and Ramskold (1996) questioned whether Dicranogmus is correctly assigned to the subfamily Trochurinae.…”

Late Ordovician and Silurian lichid trilobites from northwestern Canada: Hemiarges, Borealarges, and Richterarges

“…Borealarges and Richterarges both have member species for merly assigned to Hemiarges, and both are believed to have their roots in Hemiarges. The number of described species of Borea larges (Adrain, 1994(Adrain, , 2003 and a new, early, and somewhat unusual species assigned to Richterarges suggest that it is a good time to examine the relationships of Hemiarges, Ri chterarges, and Borealarges. Are these genera separate and dis tinct?…”

“…There are questions to be answered concerning Borealar ges, such as: 1) what are the relationships of the various species of Borealarges; 2) is there a geographic separation of species so that, for example, species of the Mackenzie Mountains are closer to each other than to the Arctic species; and 3) are there two species groups, Borealarges sensu stricto and Borealarges sensu lato, as postulated by Adrain (1994). Adrain (2003) examined the relationships of eight described Arctic species of Borealarges, and his study and conclusions are an important point of reference for this work.…”

The brachymetopid trilobite Radnoria in the Silurian (Wenlock) of New York State and Arctic Canada

“…Rich graptolite faunas occur in the shales, permitting highly resolved dating of the shelly faunas. Trilobites from these Wenlock and lower Ludlow faunas have been described in a series of papers and monographs (Adrain 1994(Adrain , 1997(Adrain , 1998(Adrain , 2003Edgecombe 1997a, 1997b;Adrain and MacDonald 1996;Ramsköld 1996, 1997). Other fossils occurring in the debris flows include common and diverse articulate brachiopods, ostracods, bryozoans, corals, gastropods, disarticulated echinoderms, bivalves, polyplacophorans, nautiloids, machaeridians, conodonts, and radiolarians.…”