Palaeobiology of Early Jurassic bakevelliid bivalves from western Canada

Early Jurassic bakevelliid bivalves from the Canadian Cordillera are examined taxonomically, morphologically, and with respect to their biogeographical affinities. Four Early Jurassic species are recognized, which belong to the genera Bakevellia, Gervillaria and Gervillella. One species, Gervillella leesi, is new. In addition, Gervillaria ashcroftensis (Crickmay) from the Bajocian (Middle Jurassic) of British Columbia and the Lower Jurassic of northern Chile has been included in this study. A functional analysis of the morphologies of the five species reveals characteristic adaptations to distinct life habits. The spectrum comprises endobyssate sediment stickers, an orthothetically attached epibyssate form, and a twisted recliner. From Late Sinemurian to Late Pliensbachian times, the bakevelliid bivalves of the western Canadian allochthonous terranes, Wrangellia, Stikinia and Quesnellia, have strongest affinities to those from northern Chile and Argentina. During this time period Bakevelliidae appear to be absent from cratonal North America. This distributional pattern is consistent with a palaeogeographical position of the terranes closer to the South American Andes than previously assumed.