PALEOBIOLOGY OF EARLY JURASSIC BAKEVELLIID BIVALVES FROM WESTERN CANADA

Early Jurassic bakevelliid bivalves from the Canadian Cordillera are e xamined taxonomically, morphologically, and with respect to their biog eographical affinities. Four Early Jurassic species are recognized, wh ich belong to the genera Bakevellia, Gervillaria and Gervillella. One species, Gervillella leesi, is new. In addition, Gervillaria ashcrofte nsis (Crickmay) from the Bajocian (Middle Jurassic) of British Columbi a and the Lower Jurassic of northern Chile has been included in this s tudy. A functional analysis of the morphologies of the five species re veals 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 stro ngest affinities to those from northern Chile and Argentina. During th is time period Bakevelliidae appear to be absent from cratonal North A merica. This distributional pattern is consistent with a palaeogeograp hical position of the terranes closer to the South American Andes than previously assumed.