187-4 Faunal diversity in Western North America during the Campanian and evidence for provincialism in Laramidian dinosaurs

Session: Phylogenetic and Computational Approaches in Paleobiology and Paleoecology (Posters)

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Previous studies have suggested that reptilian evolution during the Campanian (83.6-72.1 mya) in the western North American landmass of Laramidia was affected by a combination of orogenic processes and climatic barriers within middle paleolatitudes (48°N−58°N) that produced distinct southern and northern biomes. However, these results have been criticized due to uneven sampling methods, persistent taxonomic uncertainty in some groups, and faunal groups analyzed in isolation. Here, we quantitatively investigated faunal provinciality in reptilian (combined dinosaur, turtle, and crocodylomorph) groups across Campanian fossil sites in Laramidia. Published faunal lists were sampled at subfamily level or higher for similar-aged sites correlated in a recent broad stratigraphic revision of the Western Interior, and a few unpublished data points were added. 

A UPGMA hierarchical cluster analysis (Jaccard similarity index) roughly grouped sites in clusters of similar paleolatitude. The strongest similarities among sampled sites were among the Cerro del Pueblo, Aguja, and Kaiparowits Formations. Moderate similarity was also indicated for the following pairs of sites (in descending order): Kirtland and Masuk, Horseshoe Canyon and Two Medicine, Fruitland and Judith River, and Menefee and “Mesaverde” Formations. A PERMANOVA analysis indicated that the faunal composition of sites in the 40° to 50° group was significantly different from higher latitude groups. Results of a non-metric dimensional scaling analysis indicated that the Menefee, Fruitland, Kirtland, Masuk, and Ft. Crittenden Formations were distinctive in faunal composition from sites at other paleolatitudes, driven by the presence of Nodosauridae, Plastomenidae, Helochelydridae, and Alligatoroidea. The degree of overlap among paleolatitudinal groups suggests the highest faunal cohesion among sites occurred above 50° paleolatitude and including Kaiparowits and Wahweap. The diffuse arrangement of sites within the 40° to 50° group may reflect greater ecological heterogeneity and broader habitat representation. 

The results obtained here support north-south provincialism of reptilian faunal assemblages in western North America during the Campanian. Differences in distributions among the faunal groups likely relate to differences in habitat and vicariance patterns among predominately aquatic turtles, crocodylomorphs, and terrestrial dinosaurs. The latitudinal provincialism revealed herein aligns with the current understanding of warm southern and cool northern biomes in Laramidia during the Campanian, where cyclical sea level changes in the Western Interior Seaway influenced basin geometry and water distribution with broad impacts on the distribution of continental biodiversity.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11277

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