Abstract
ALTHOUGH the occurrence of fossil mammals in North American Upper Cretaceous rocks has long been known1, only since the application in 1956 of new collecting techniques2 have large samples of skeletal—especially dental—remains of Late Cretaceous mammals been recovered3. Important systematic studies have been based on these samples during the past decade. Maestrichtian. (latest Cretaceous) assemblages from sites in New Mexico (W. Clemems, personal communication), Wyoming3, Montana4 and Alberta5 include several placental (Eutheria) orders, and many multituberculates (Allotheria) and didelphoid marsupials (Metatheria). Assemblages of late Campanian age in Montana6 and Alberta (unpublished results) are nearly as rich in multituberculates and marsupials, but are relatively poor in placentals, with only two orders (Insectivora and Deltatherida) represented.
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