NEW INSIGHTS INTO THE EVOLUTIONARY HISTORY AND BIOGEOGRAPHY OF THE EARLY CAMBRIAN OLENELLINE TRILOBITES

The “Nevadioidea” represents a paraphyletic grade of Early Cambrian trilobites nested within the diverse Early Cambrian group the Olenellina. Phylogenetic analyses have proven useful in understanding the position of this “superfamily” within the Olenellina. Discovery and taxonomic analysis of new Lower Cambrian trilobite material collected from the Sekwi Formation of the Makenzie Mountains, Northwest Territories, Canada, along with a phylogenetic study, are the focus here. They reveal new insight into the evolutionary history of the “nevadioids”. Three new species of Bradyfallotaspis are presented; further, other material is discussed that indicates a significant range expansion for Nevadia ovalis which had previously only been known from northwestern Sonora, Mexico. This relatively broad geographic range is atypical for olenellines, which are usually geographically restricted, and may prove useful in biostratigraphic correlation. Results from a phylogenetic analysis incorporating other olenellines as well as this new material are also described. The phylogeny indicates that some of the material from the Northwest Territories is referable to Judomia, rather than Paranevadella. This provides further support for a close biogeographic relationship between Siberia and Laurentia.