38 Laramidia: Biota, Stratigraphy, and Paleogeography of the Late Cretaceous of Western North America II

Tuesday, 20 May 2025
1:30 PM - 3:15 PM
Cascade E

NEW VERTEBRATE OCCURRENCES IN THE UPPER CRETACEOUS (CAMPANIAN–MAASTRICHTIAN) ALMOND FORMATION, WYOMING, USA

Paper number: 38-2
Program: Theme Sessions
Time: 1:45 PM – 2:00 PM

Authors

Abstract

During the Campanian stage of the Late Cretaceous, western North America was an isolated landmass known as Laramidia. Extensive collecting from Campanian deposits of Laramidia has revealed patterns of regional endemism, with distinct but contemporary faunal assemblages in ‘northern’ (Alaska, Alberta, Montana) and ‘southern’ (southern Utah, New Mexico, Texas, Coahuila [Mexico]) Laramidia. Diagnostic vertebrate fossils from the Campanian of ‘central’ Laramidia (northern Utah, Colorado, Wyoming), however, remain limited. The Almond Formation of Southern Wyoming is positioned in ‘central’ Laramidia and includes terrestrial deposits from the latest Campanian and earliest Maastrichtian (~73.5–72 Ma). The Central Laramidia Project was initiated in 2021 to recover diagnostic fossils from the Almond Formation and has since discovered dozens of significant vertebrate localities. A new partial skull of a large chasmosaurine ceratopsid includes a squamosal and the diagnostic posterior parietal. This specimen is distinct from northern taxa and instead shares features with Pentaceratops and related southern forms and as such may represent the northernmost occurrence of this lineage. Hadrosaurids collected thus far include a large associated skull, an articulated skeleton with a partial skull, and portions of a large, partially articulated skeleton with skin impressions. A nodosaurid is represented by several osteoderms, and a thescelosaurid-like taxon is represented by an associated dentary and dorsal vertebra. Theropods are represented by unguals referable to Ornithomimidae. Crocodylomorph osteoderms and teeth indicate the presence of a globidont form similar to Brachychampsa. Turtles include taxa common to both ‘northern’ and ‘southern’ Laramidia (cf. Basilemys sp., cf. Compsemys., cf. Adocus) and also Denazinemys sp., previously recognized only from Utah and New Mexico. Fishes are represented by lepisosteid scales, rhinobatoid teeth, and numerous vertebrae, ribs, teeth, and an associated skull of the amiid Melvius. The presence of Denazinemys and a new member of the Pentaceratops lineage in ‘central’ Laramidia by the latest Campanian indicates that these lineages had by this time achieved a broad geographic distribution across the southern and central coastal plains of this landmass.

Geological Society of America Abstracts with Programs. Vol. 57, No. 5

doi: 10.1130/abs/2025RM-409844

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