An elasmobranch assemblage from the terrestrial-marine transitional Lethbridge Coal Zone (Dinosaur Park Formation: Upper Campanian), Alberta, Canada

The change in depositional environments observed in the Cretaceous (Upper C ampanian) strata in the region of Dinosaur Provincial Park, Alberta, from t he proximal coastal plain deposits of the Oldman Formation to the lowland c oastal plain deposits of the Dinosaur Park Formation, reveals an associated change in faunal composition. An assemblage collected from a microvertebra te site in the paralic deposits of the Lethbridge Coal Zone (uppermost Dino saur Park Formation) reflects an increasing marine influence. Elasmobranch (sharks and rays) remains are the most abundant, both in terms of number of overall taxa and number of elements, and they are the best-preserved speci mens. However, several brackish-water-tolerant osteichthyan taxa, and four reptile taxa (two marine and two terrestrial), were also recovered, althoug h they exhibited evidence of extensive taphonomic reworking. The elasmobranch fauna collected from the Dinosaur Park locality is uncommo n for vertebrate microfossil assemblages in the Dinosaur Park Formation of Alberta and in equivalent beds in Montana. Seven of the 10 taxa collected f rom this site [Cretorectolobus olsoni Case, 1978; Eucrossorhinus microcuspi ciatus Case, 1978; Odontaspis aculeatus (Cappetta and Case, 1975); Archneol amna kopingensis judithensis Siverson, 1992; Protoplatyrhina renae Case, 19 78; Ischyrhiza mil a Leidy, 1856; and Ptychotrygon blainensis Case, 1978] a re recorded for the first time from the uppermost section of the Judith Riv er Group in Alberta; Carcharias steineri (Case, 1987), represents the first occurrence within the upper Judith River Group from either Alberta or Mont ana.