Early diversity of acanthomorph fishes in fresh waters of the Late Cretaceous

Late Cretaceous acanthomorph fishes are well represented in freshwater vertebrate microfossil localities in the Western Interior of North America but are not well known from articulated specimens. Microfossils—isolated disarticulated elements—provide data on diversity and distribution but can be difficult to assign to known lineages. Articulated specimens are needed to evaluate the evolutionary relationships of early acanthomorphs, but these are rarely preserved in fluvial beds, limiting our understanding of the taxa present in these environments. An exceptional freshwater locality that preserves a diverse assemblage of small articulated specimens is Pisces Point sampling the Scollard Formation of Alberta, Canada. Known taxa in the locality include two osteoglossomorphs, an esocid, the percopsiform (Acanthomorpha) Lindoeichthys albertensis Murray et al., 2019, and the otophysan Acronichthys maccagnoi Liu et al., 2025. Here we describe two additional acanthomorph fishes: a polymixiiform tentatively in family Boreiohydriidae, and a percomorph of uncertain relationships. These specimens, along with the previously named Pisces Point percopsiform, indicate that at least three distantly related acanthomorph lineages were present in fresh waters of North America by the late Maastrichtian, and increase our understanding of the acanthomorph evolutionary and geographic diversity prior to the end of the Cretaceous.