The diversity and distribution of nonmarine teleost fishes in the Western Interior of North America during the late Maastrichtian is documented based on isolated elements from vertebrate microfossil localities in the Hell Creek Formation of Montana, the Lance Formation of Wyoming, and the Scollard Formation of Alberta. A minimum of 20 taxa are recognized based on >1900 abdominal centra and tooth-bearing elements. These include two elopomorphs, six osteoglossomorphs, three ostariophysans, one esocid, six acanthomorphs, and two taxa of unknown relationships. These assemblages differ from late Campanian assemblages in the absence of the Clupeomorpha and the presence of the Perciformes. Within the Hell Creek Formation, we record patterns in the relative abundances of the most abundant taxa leading up to the Cretaceous–Paleogene (K–Pg) boundary. Most notably, acanthomorphs increased in abundance upsection, whereas a group of osteoglossomorphs, represented by Coriops and (or) Lopadichthys, concurrently decreased in abundance. Conversely, some teleosts exhibited more stable or slightly fluctuating relative abundances throughout the formation (Wilsonichthyidae, Esocidae). These late Maastrichtian teleost assemblages are of higher diversity than an early Eocene assemblage from Wyoming preserved under similar taphonomic conditions. This pattern suggests either that lower Cenozoic deposits in the Western Interior are insufficiently sampled or that the K–Pg mass extinction event adversely affected nonmarine teleosts.

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