Microvertebrate Accumulations of WY and MT

Hey everybody!

My name is Sean Moran and I am a rising senior geology major/biology minor at the College. About 2 summers ago I grew interested in particularly diverse vertebrate fossil accumulations commonly found in the Mesozoic Era (~250 to 65 million years ago). These “microsites” as they are commonly called, contain fossils of a large amount of taxa and, therefore, provide a fantastic representation of the paleoecology of the area where the sites were deposited. Fossils ranging from dinosaur teeth, turtle carapace fragments, reptilian teeth and jaws, fish scales, to assorted vertebrae and limb bones are commonly found. Although the deposition of these accumulations has been heavily debated over the past few decades, a study published within the last few months suggested that they are first deposited in lacustrine (lake/stream) environments and commonly reworked by fluvial or river processes. Unfortunately, because these microsites are usually found in rock formations that contain more “interesting” fossil specimens (dinosaur skeletons, early mammals, etc.), the importance of these sites have been largely ignored in the scientific literature.

For my project I am planning on looking at the microsites from two Cretaceous (~145-65 million years ago) formations that are exposed in Montana and Cloverly. I spent most of last summer at the Smithsonian’s National Museum of Natural History (NMNH) in Washington, D.C. becoming more acquainted with processing and studying these microsites with Dr. Matthew Carrano. The NMNH has been collecting microvert fossils from the Early Cretaceous (~120 million years ago) Cloverly Formation of Wyoming. During this internship I learned how to collect these sites in the field (near Cody, WY) and how to study the fossils when brought back to the lab.

Using this knowledge, I will be performing 2-3 weeks of field work in the Late Cretaceous (~65 million years ago) Hell Creek Formation in northeastern Montana, which preserves some of the last dinosaurs before they disappeared at the Cretaceous-Tertiary Boundary (K-T). I am planning on collecting and processing fossils from six Hell Creek microsites (3 lacustrine and 3 fluvial) and examing the paleoecology (abundance, diversity, and species evenness), taphonomy (preservational factors of each fossil), and depositional environment and comparing these microsites to those that have been collected by the Smithsonian in the Cloverly Formation to look for shifts in ecology, taphonomy, and/or depositional environments over the 50 million years between the two formations.

I really enjoy working with microvertebrate fossils and interpreting what the environments and ecologies must have been like more than 65 million years. I’m looking forward to spending my summer with these fossils both out west in “Big Sky Country” for field work and for lab work in the ‘burg.


  1. bdnorris says:


    Your work seems extremely promising, and the field work sounds like it will be an incredible experience—I find it fascinating that you’re able to reconstruct a history dating back millions of years. I have a general question, as I’m completely unfamiliar with this type of research: what sort of differences are you expecting to find between the microsites you visit and the ones that have been collected in the Smithsonian? What are the implications of the shifts in ecology and taphonomy that you may find?