Pediomys Marsh, a primitive marsupicarnivore, is the most common therian mammal known from the Upper Cretaceous Oldman Formation, Alberta, where it is represented by at least four species. The first, P. clemensi Sahni, appears closely related to the Lancian P. cooki Clemens; other species, poorly represented by fossils, resemble the Lancian P. elegans Marsh and P. hatcheri respectively; a final species, which is new, is interpreted as the direct ancestor of the Lancian P. krejcii Clemens. Pediomys shows trends toward enhancement of a crushing rather than a shearing function of the postcanine dentition and, consequently, seems not ancestral to the Cenozoic 'dog-like' marsupials of Australia and South America, contrary to recent suggestions elsewhere.

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