Article: Burlingiid trilobites from Norway, with a discussion of their affinities and relationships

Four Middle and Upper Cambrian burlingiid trilobites from the Oslo Region, Norway, are described including Burlingia angusta sp. nov. from the Ptychagnostus punctuosus Zone and Schmalenseeia athrotryphe sp. nov. from the lower part of the Lejopyge laevigata Zone. New complete material previously attributed to Schmalenseeia jagoi Whittington is assigned to Burlingia. Cladistic analysis supports the genera Burlingia and Schmalenseeia as currently understood, including the placement of the controversial middle Middle Cambrian Schmalenseeia acutangula Westergard in Schmalenseeia, even though it lacks typical characters of the genus such as the median ridge on the preglabellar field. The analysis also supports burlingiid monophyly, and suggests that Schmalenseeia was derived from a broadly Burlingia-like ancestor, with S. acutangula displaying how the transition may have occurred. The broader relationships of Burlingia remain obscure, although similarities between burlingiids and the arthropod Kleptothule from the Early Cambrian Sirius Passet fauna are discussed: these include overall form, lack of functional hinges in the thorax, and details of the cephalic region. It is unclear whether these similarities represent general progenetic features, are functional convergences or, less likely, represent a genuine relationship.