BIOTIC INTERACTIONS AND FOOD CHAIN/WEB OF A COMMUNITY FROM UPPER CRETACEOUS OF SOUTHWESTERN MANITOBA, CANADA

The Upper Cretaceous Millwood Member (Campanian) of the Pierre Shale is well exposed in Russell area of southwestern Manitoba. Bulk sampling along a fossiliferous horizon near the middle part of the member on an outcrop at Harrowby revealed a fairly diverse time-averaged community dominated by mollusks. Over 900 macrofossil specimens are assigned to: Scaphopoda: Dentalium gracile; Gastropoda: Euspira obliquata; Anomalofusus sp.; Graphidula culbertson; Graphidula cretacea; Mesalia sp.; Oligoptycha concinna; and fasciolariid gen. et sp. indet.; Pelecypoda: Astarte sp.; Inoceramus sp.; Cephalopoda: Baculites scotti, and Hoploscaphites sp.; and Decapoda (a crab): Cretacocarcinus smithi. Previous study recovered Foraminifera (e.g. Bathysiphon, Ammodiscus, Glomosspira, Haplophragmoides) from similar horizon at the neo-stratotype of Millwood Member about 15 km south of the study site, it is feasible to include these microorganisms in the community. Besides body fossils as direct evidence of community composition, trace fossils may help uncover some other components. Abundant bioerosion (boring) traces on Dentalium, Euspira, and Astarte are assigned to Maeandropolydora sulcans, whose maker is generally believed to be spinoid polychaetes----as unpreserved elements of the community. Well preserved and commonly presented predatory drilling traces Oichnus paraboloides on Dentalium, Mesalia, Euspira, Astarte., and fasciolariid gen. et sp. indet. are interpreted to be made by the only naticid gastropod Euspira in the community. Crushing predation traces on Dentalium and Euspira are interpreted to be caused by the crab Cretacocarcinus. On the basis of these biotic interactions within the benthic community (i.e. not considering ammonites) and the general understanding of feeding habit of living Dentalium, reconstruction of the food chain/web is attempted: Foraminiferaà Dentaliumà Euspiraà Cretacocarcinus; Foraminiferaà Dentaliumà Cretacocarcinus; Mesalia, Euspira, Astarte, and fasciolariid gen. et sp. indet. à Euspiraà Cretacocarcinus. The ammonites Baculites and Hoploscaphites may have been on the top of the food chain/web in the whole community preserved.