A new Early Eocene (Lostcabinian) mammal assemblage from the Main Body of the Wasatch Formation, Northern Green River Basin; The Pinnacles, Sweetwater Co., Wyoming

Abstract

Taphonomy of fluvially deposited microvertebrates and systematic paleontology of the Pinnacles buttes in the northwest Great Divide Basin is examined. The Pinnacles buttes contain an early Eocene mammal assemblage of over 900 cataloged specimens from several prolific University of Michigan localities. The diverse assemblage is represented by a minimum of 56 species of 30 families. Sedimentology of the Main Body of the Wasatch formation in the basin margin of the Great Divide has not previously been examined. This thesis provides the first detailed descriptions and measurements of these specimens and explores the sedimentological and taphonomical environments in which this diverse assemblage accumulated in. The microvertebrate fossils were collected from chute-modified channel bar deposits at two fossiliforous horizons in the uppermost 40-50 m of the Main Body of the Wasatch Formation. Concentration of fossils to discrete horizons vertically associated with crevasse splays and gravel bed streams suggests that proximal channel facies played a pivotal role in preservation of fossils in this setting.