ASSESSMENT OF TROPHIC STRUCTURE OF CRETACEOUS COMMUNITIES BASED ON STABLE NITROGEN ISOTOPE ANALYSES

New deltaN-15 data suggest the retention of an indigenous signal in an cient high molecular weight organic material. These data open the poss ibility of obtaining new paleoecological information, based on isotopi c analyses, on ancient, well-preserved fossil communities. Stable carb on and nitrogen isotope analyses were performed on high molecular weig ht organic material isolated from 22 taxa of Late Cretaceous vertebrat es (judith River Formation, Alberta, Canada). The majority of deltaC-1 3 and deltaN-15 values (-27 parts per thousand to -23 parts per thousa nd and 4 parts per thousand, 12 parts per thousand, for deltaC-13 and deltaN-15, respectively) are similar to those reported for modern cons umers. An assessment of trophic levels based on deltaN-15 is consisten t with previous interpretations of food web structure derived from pal eoecological interpretations. Among terrestrial consumers, carnivorous theropods (tyrannosaurids and dromaeosaurids) have high deltaN-15 val ues (6.6 parts per thousand +/-0.4 parts per thousand and 7.9 parts pe r thousand, respectively) relative to those of the dominant megaherbiv ore (hadrosaurids, 4.7 parts per thousand +/-0.5 parts per thousand. W ithin aquatic environments, the values of deltaN-15 of the bowfin Amia (11.6 parts per thousand) and plesiosaur (11.0 parts per thousand) di stinguish the piscivorous tendencies of these organisms from those of lower trophic level consumers such as the benthic feeding sturgeon Aci penser and the turtle Aspideretes (deltaN-15 = 5.1 parts per thousand and 4.5 parts per thousand, respectively). The correlation in trophic position between deltaN-15 values and paleoecological evidence is unli kely to be coincidental.