Dinosaur Paleoecology, Judith River Formation, South CentralMontana

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The Judith River Formation of Montana has historical significance as the source of America's first dinosaur fossils, which were described in Philadelphia by Joseph Leidy in 1856. However, the formation has since been frustrating as a source of dinosaur fossils. Beds of similar age farther north in Alberta and farther west in north central Montana have proved to be more productive. A dinsosaur bonebed discovered in 1981 in Judith River sediments near Shawmut, south central Montana, is the richest yet found in the Montana Judith River, and the southernmost productive site from this formation. Among the taxa represented are a new genus of ceratopsid (Avaceratops lammersi Dodson 1986), a giant hadrosaur, very rare postcrania of a pachycephalosaurid, and juvenile hadrosaurs and ceratopsids that occur with a higher frequency here than at most other contemporary sites. Work initially focused on the Careless Creek Quarry, but prospecting has revealed a number of sites in the area, so it is proposed to establish an environmental transect from west to east towards the Interior Seaway. A 25 km transect has been established, at the eastern end of which are found oysters, sharks and teleost fishes. Analysis of faunal changes across the transect will permit a better understanding of the ecological determinants of dinosaur distribution.