Palm fronds from western Canada are the northernmost palms from the Late Cretaceous of North America and may include the oldest Arecaceae

Abstract

Palm leaf fossils are common from Late Cretaceous floras in the United States, but Late Cretaceous Canadian palm records are limited largely to Nanaimo Group strata of British Columbia, with only anecdotal records from east of the Rocky Mountains. Here we report Late Cretaceous leaf fossils from Alberta and Saskatchewan, Canada. Segment angles with the rachis or costa are investigated as an additional character to distinguish costapalmate from pinnate and entire-pinnate palm leaves. The leaf fossils from Alberta and Saskatchewan represent costapalmate-palms (Sabalites), in contrast to the relatively common entire-pinnate palm fossils known from the Coniacian–early Campanian lower Nanaimo Group of British Columbia (e.g., Geonomites imperialis; potentially the oldest known North American palm) and the Campanian Two Medicine Formation of Montana (cf. Phoenicites). The presence of fossil palms in the Campanian to Maastrichtian of Alberta and Saskatchewan constrains climate reconstructions for the Late Cretaceous high mid-latitudes of North America (c. 55° N) to exclude significant freezing episodes. Additionally, we update the nomenclature for G. imperialis, renaming it as a species of Phoenicites, and briefly consider its value to understanding the evolution of pinnate palms. Further, we challenge the interpretation of Sabalites magothiensis as a costapalmate species and reassess the age of S. carolinensis as late Campanian.