New mammalian fossils from the Upper Cretaceous Oldman Formation, Alberta, pertain to three species of the marsupial Alphadon Simpson. One of these species, A. praesagus (Russell), is ancestral to the Lancian A. rhaister Clemens. The second, closely related but not ancestral to the Lancian A. marshi Simpson, is new, and the third, A. halleyi Sahni, is closely related to the Lancian A. lulli Clemens, as had been earlier supposed from fossils from the Judith River Formation, Montana. The phylogenetic relationships of Alphadon are discussed.

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