The effect of the Cretaceous-Paleogene (K-Pg) (formerly Cretaceous–Tertiary, K–T) mass extinction on avian evolution is debated, primarily because of the poor fossil record of Late Cretaceous birds. In particular, it remains unclear whether archaic birds became extinct gradually over the course of the Cretaceous or whether they remained diverse up to the end of the Cretaceous and perished in the K–Pg mass extinction. Here, we describe a diverse avifauna from the latest Maastrichtian of western North America, which provides definitive evidence for the persistence of a range of archaic birds to within 300,000 y of the K–Pg boundary. A total of 17 species are identified, including 7 species of archaic bird, representing Enantiornithes, Ichthyornithes, Hesperornithes, and an Apsaravis -like bird. None of these groups are known to survive into the Paleogene, and their persistence into the latest Maastrichtian therefore provides strong evidence for a mass extinction of archaic birds coinciding with the Chicxulub asteroid impact. Most of the birds described here represent advanced ornithurines, showing that a major radiation of Ornithurae preceded the end of the Cretaceous, but none can be definitively referred to the Neornithes. This avifauna is the most diverse known from the Late Cretaceous, and although size disparity is lower than in modern birds, the assemblage includes both smaller forms and some of the largest volant birds known from the Mesozoic, emphasizing the degree to which avian diversification had proceeded by the end of the age of dinosaurs.

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Acid etching of a shell-bed zone has enabled us to reclaim numerous fish remains for the Niobrara Formation (Coniacian) of east-central Saskatchewan, including teeth of the following new taxa: Odontaspis saskatchewanensis sp.nov., Synodontaspis lilliae sp.nov., and Cretomanta canadensis gen. et sp. nov. These are associated with remains of Ptychodus cf. Ptychodus rugosus Dixon, Cretodus sp., Cretoxyrhina mantelli (Agassiz), Squalicorax falcatus (Agassiz), and Rhinobatos sp. This is the most northern occurrence from Canada of a Niobrara-age selachian fauna.

The first occurrence from the Frenchman Formation (late Maastrichtian) of juvenile ceratopsians (Chasmosaurinae) is reported here based on two postorbital horn-cores. The sutures confirm that the frontal attaches along the medial side of the postorbital much like that in Centrosaurinae and cannot be used as a tool for distinguishing the two ceratopsid subfamilies.

Late Cretaceous marine turtles are rare in Canada, but specimens are known from three formations: Toxochelys latiremis Cope and Protostega sp. from the Pierre Shale, Pembina Member (lower Campanian); Lophochelys niobrarae Zangerl and Chelonioidea genus indet. from the Bearpaw Formation (upper Campanian); Protostegidae genus indet. and one other taxon from the Niobrara Formation (Coniacian).The Canadian records of the listed taxa constitute the northernmost limits of their known range and may represent their northern limits in the Cretaceous inland sea. Taxonomic diversity and relative abundance of turtles in the Canadian samples are significantly less than in comparable faunas to the south. Cool marine climates may have excluded local nesting and discouraged migrations into northern areas.