BURGESS SHALE-TYPE FOSSILS FROM A LOWER CAMBRIAN SHALLOW-SHELF SEQUENCE IN NORTHWESTERN CANADA

FOSSIL Lagerstatten comparable to that of the Burgess Shale potentiall y provide the detail necessary to resolve and assess the so-called Cam brian Explosion of multicellular life(1,2); distributional and taphono mic biases, however, often limit the generalizations that can be drawn . Here I report widespread occurrences of Burgess Shale-type fossils i n shallow-shelf sediments of the Lower Cambrian Mount Cap Formation, D istrict of Mackenzie, Northwest Territories, Canada. These borehole as semblages significantly expand the known geographical and ecological r ange of such fossil biotas and document the early appearance of both w iwaxiid polychaetes and filter-feeding crustaceans. The ability of thi s latter group to exploit microplanktic primary productivity marks a f undamental shift in trophic structuring and may distinguish Phanerozoi c from pre-Phanerozoic ecosystems.