VERTEBRATE MICROFOSSILS FROM THE HANSON BONEBED, LANCE FORMATION (MAASTRICHTIAN), NIOBRARA COUNTY, WY, USA

Vertebrate microfossil sites play an essential role in describing the composition and diversity of paleocommunities. The Lance Formation, an upper division of the Maastrichtian, is an extensive deposit of Mesozoic vertebrate fauna located in eastern Wyoming. Despite thousands of fossils having been recovered from the Lance Formation, very little is known about Lancian microsites. During our 2021 summer excavation, we discovered over 50 teeth of the relatively rare Pectinodon bakkeri and other microfossils in a western harvester ant's nest near the main Hanson Bonebed.

To explore this site further, we sampled 90 liters of substrate from each of 12 plots, located 8 meters apart around the ant nest. Approximately 700 identifiable elements, representing nearly 30 taxa were collected. Strangely, the vast majority of specimens collected were from one specific plot. The groups represented with the largest number of elements were the Lepistosteidae (gar; n = 109), Edmontosaurus annectens (hadrosaur; n = 65), Pectinodon bakkeri (Troodontid; n = 53), Amiidae (bowfin; n = 37), and Alligoridae, such as Brachychampsa sp. (n = 43) and Leidyosuchus sp. (n = 12). Teeth comprised 55% of the identifiable elements followed by scutes and scales (22%), vertebrae (15%), jaw pieces (7%), and avian claws and theropod long bones (1%). Identifiable elements constituted between 1.5% and 5% of all fossils collected at each plot.

This new microsite represents a complex paleo-environment, consisting of a varied assemblage of both aquatic and terrestrial creatures. Continued work on this site will better enable us to understand the taphonomical processes involved in constructing this microsite and facilitate comparisons between microsites from the Lance and Hell Creek Formations, which are known to contain similar fauna.