Palynological and mesofossil analyses of an Edmontosaurus bonebed from the Late Cretaceous Lance Formation: Paleoecological insights

The fossiliferous strata of the Maastrichtian-aged Lance Formation in Wyoming, although broadly coeval with the better-known Hell Creek Formation, remain comparatively understudied. A detailed examination of a recently discovered Edmontosaurus annectens bonebed in the Lance Formation opened a new window into the last Cretaceous terrestrial ecosystems of present-day North America. This locality, which yielded a wealth of vertebrate remains but also macro-, meso-, and micro-palaeobotanical remains, now serves as a focal point for renewed paleoecological analysis of the Lance Formation. This study presents palynological and mesofossil data from sediments associated with the Edmontosaurus bonebed, with particular emphasis on a peculiar aquatic palynoflora. Notably high abundances of Azolla, an ecologically restricted aquatic fern, were recovered from multiple stratigraphic levels within and surrounding the bonebed horizon. The presence of Azolla megaspores, along with other freshwater-indicative palynomorphs such as Pediastrum, Botryococcus, and Gunnera, supports deposition in a freshwater floodplain setting with densely vegetated still-water bodies. Moreover, the concentration of Azolla and associated aquatic palynoflora in and around the bonebed horizon may offer new insights into the paleoecology of Edmontosaurus, including potential habitat preferences and feeding behaviors. Stratigraphic analysis of the floral assemblages below, within, and above the bonebed also suggests notable shifts in plant community composition over time, possibly linked to environmental changes in the latest Maastrichtian. This integrated paleoecological and palynological perspective enhances our understanding of the Lance Formation ecosystems, and underscores the importance of expanding research beyond more extensively studied rock units like the Hell Creek Formation.