A NEW PALEOBOTANICAL RECORD FROM THE NESLEN FORMATION (UPPER CRETACEOUS: CAMPANIAN) OF EASTERN UTAH, USA

A new paleobotanical record from the Neslen Formation (Upper Cretaceous: Campanian) of eastern Utah, USA

Whitney Greaves Bell, S. Augusta Maccracken, Joshua R. Lively

Upper Cretaceous strata deposited in basins along the eastern shore of the Western Interior Seaway preserve abundant vertebrate, invertebrate, and plant fossils, notably those from Campanian deposits. Previous work on fossil assemblages from the Laramidian subcontinent have supported the presence of basin-scale endemism and/or provinciality in some vertebrate taxa. However, Laramidian floral biogeography is poorly known and appears to be more complex than that of the dinosaurian fauna. The Campanian Neslen Formation in eastern Utah provides an opportunity to contribute to Laramidian floral biogeography, as it lies between the proposed northern and southern provinces and represents paralic environments between the Sevier Orogenic Belt to the west and the seaway to the east.

In this contribution, we provide an initial paleobotanical overview of the Neslen Formation and identify plant fossils from localities previously collected by the Prehistoric Museum and the Denver Museum of Nature & Science. Plant fossils were discovered in fine grain sandstones and mudstones using both traditional quarrying and surface collection techniques. Fossil leaves were classified using the morphotype system.

To date, there is a modest richness of plants in the Neslen Formation, with one locality in particular containing >30 plant morphotypes. We identified multiple ferns, including an aquatic fern in the genus Hydropteris, as well as gymnosperms in the genera Araucaria and Protodammara. Notably, Protodammara are relatively rare in Laramidian floras and were mostly recovered from muddy facies in the Neslen Fm. Angiosperms were a diverse component of the Neslen flora, including both terrestrial and aquatic taxa, such as the floating aquatic monocot Cobbania sp., the terrestrial monocot Sabalites, and the terrestrial dicot “Ficus” planicostata, which are all common elements of Laramidian floras. Overall, the Neslen flora identified thus far is typical of many Campanian formation floras spanning north-south along Laramidia, with the possible exception of Protodammara.