Latest Cretaceous (Lancian) mammalian faunas of the Western Interior of North America are mostly known from the northern Great Plains and coastal lowland paleoenvironments. Here, we describe a sample of 143 multituberculate mammal teeth from the Lance Formation of southwestern Wyoming. The specimens, which are from two independent collections made in the 1970s by the University of California Museum of Paleontology and the University of Wyoming Geological Museum, are part of the best-sampled local fauna from the central part of the Western Interior. Deposits of the Lance Formation in this region are on the eastern flank of the Rock Springs Uplift near Black Butte Station. The Black Butte Station local fauna was farther west and possibly paleoenvironmentally distinct from most other Lancian local faunas known. The fossil assemblage preserves eight genera and 11 species of multituberculates. There are many common Lancian taxa, a high relative abundance of Cimexomys, the second published occurrences of Parikimys and Paressonodon, and a new species of Cimolodon. Cluster and ordination analyses of multituberculate abundance data from well-sampled Western Interior local faunas show that the Black Butte Station local fauna is distinct from all other local faunas and that variation among mammalian local faunas in composition is correlated with latitude, though paleoenvironmental, temporal, and taphonomic differences may also be factors. Results highlight that explorations in undersampled regions and paleoenvironments are critical to a more complete understanding of the Cretaceous-Paleogene transition.
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