NewMiddleCambrian bivalved arthropods from theBurgessShale (BritishColumbia,Canada)

Abstract

AbstractThe morphology of two new bivalved arthropods,Loricicaris spinocaudatusgen. et sp. nov. andNereocaris briggsisp. nov. from themiddleCambrian (Series 3,Stage 5)BurgessShaleFormation (CollinsQuarry locality onMountStephen,YohoNationalPark,BritishColumbia,Canada), is described. The material was originally assigned to the genusBranchiocaris, but exhibits distinctive character combinations meriting its assignment to other taxa.Loricicaris spinocaudatuspossesses an elongate and spinose abdomen comparable to the contemporaneousPerspicarisandCanadaspis, as well as chelate second head appendages and subtriangular exopods, comparable toBranchiocaris.Nereocaris briggsipossesses a laterally compressed carapace, elongate and delicate appendages and a medial eye located between a pair of lateral eyes on a rhomboidal eye stalk. Although undoubtedly congeneric withNereocaris exilisfrom a slightly younger horizon of theBurgessShaleFormation,N. briggsidiffers in overall proportions and segment number, warranting assignment to a new species. The newly described taxa were coded into an extensive cladistic analysis of 755 characters, and 312 extinct and extant panarthropods, including a variety ofCambrian bivalved arthropods from both theBurgessShale and theChengjiangLagerstätten. Cambrian bivalved arthropods consistently resolved as a paraphyletic assemblage at the base ofArthropoda. Important innovations in arthropod history such as the specialization of the deutocerebral head appendages and a shift from a nekton‐benthic deposit feeding habit to a benthic scavenging/predatory habit, the symplesiomorphic feeding condition ofEuarthropoda (crown‐group arthropods), were found to have occurred among basal bivalved arthropods.