Sampling Vertebrate Microfossils in Upper Cretaceous (Maastrichtian) Hell Creek Formation Microsites of Garfield County, Montana, U.S.A.

Ouellette, Noel

Sampling Vertebrate Microfossils in Upper Cretaceous (Maastrichtian) Hell Creek Formation Microsites of Garfield County, Montana, U.S.A.

Persistent URL

https://hdl.handle.net/10456/57685

Author(s)

Ouellette, Noel

Date Issued

April 5, 2024

Abstract

North America’s western interior is known for some of the most extensive and abundant fossil beds in the world. Notably, the Hell Creek Formation (Upper Cretaceous Period-Maastrichtian Age) of the northern Great Plains region preserves a highly diverse paleocommunity. These organisms inhabited this area directly prior to the Cretaceous-Paleogene Extinction, which followed the Chicxulub Bolide Impact, around 66 Ma. The majority of the formation was deposited by rivers draining eastward into the shrinking Western Interior Seaway, with their sediments originating in the young Rocky Mountains. The current action of these rivers resulted in localized accumulations of small fossils, commonly referred to as microsites. Microsite deposits found within the Hell Creek can include an incredible diversity of fossils which can provide important details about the often underrepresented components of the ecosystem, as size bias trends toward smaller fossils, rather than the larger bones of megafaunal dinosaurs. This study seeks to understand the relative abundances of five microsites sampled in late May, 2023, and compare the results between sampling strategies. Two primary methods are used to sample from microsite localities: surface collection and matrix extraction. Through matrix sampling, all fossils in a given sample can be found in a lab setting, however surface collection in the field suffers from the pitfalls of human visual bias and is less comprehensive as a result. Faunal assemblages from both groups were represented by majority aquatic and amphibious taxa. Turtle shell fragments were the most common identifiable group from surface collections, while a large percentage of that assemblage consisted of unidentifiable tumbled bone fragments. Bony fish were the most common component of the matrix assemblage.

Major

Geology

First Reader(s)

Whitenack, Lisa B.