Richard K. Stucky

Climate directly influences Eocene mammal faunal dynamics in North America.

The modern effect of climate on plants and animals is well documented. Some have cautioned against assigning climate a direct role in Cenozoic land mammal faunal changes. We illustrate 3 episodes of significant mammalian reorganization in the Eocene of North America that are considered direct responses to dramatic climatic events. The first episode occurred during the Paleocene–Eocene Thermal Maximum (PETM), beginning the Eocene (55.8 Ma), and earliest Wasatchian North American Land Mammal Age (NALMA). The PETM documents a short (<170 k.y.) global temperature increase of ≈5 °C and a substantial increase in first appearances of mammals traced to climate-induced immigration. A 4-m.y. period of climatic and evolutionary stasis then ensued. The second climate episode, the late early Eocene Climatic Optimum (EECO, 53–50 Ma), is marked by a temperature increase to the highest prolonged Cenozoic ocean temperature and a similarly distinctive continental interior mean annual temperature (MAT) of 23 °C. This MAT increase [and of mean annual precipitation (MAP) to 150 cm/y) promoted a major increase in floral diversity and habitat complexity under temporally unique, moist, paratropical conditions. Subsequent climatic deterioration in a third interval, from 50 to 47 Ma, resulted in major faunal diversity loss at both continental and local scales. In this Bridgerian Crash, relative abundance shifted from very diverse, evenly represented, communities to those dominated by the condylarth Hyopsodus. Rather than being “optimum,” the EECO began the greatest episode of faunal turnover of the first 15 m.y. of the Cenozoic.

Geological Remote Sensing Of Palaeogene Rocks In The Wind River Basin, Wyoming, Usa

Remote sensing studies of Palaeogene sediments in the Wind River Basin have concentrated on mapping stratigraphic units, sedimentary features and facies, and structural patterns. New TM principal component images for the central and eastern Wind River Basin along with geological investigations and spectral analyses have allowed: (1) mapping of the Fort Union, Wind River and Wagon Bed formations (fm.) and their subunits; (2) recognition of two new subunits in the Wind River Fm., one of which can be traced for 75 km; (3) determination of sediment source and depositional environment of units within the Wind River Fm.; (4) correlation of the Wagon Bed Fm. across the basin; and (5) apparent confirmation of different sources of volcanic debris in the western and southeastern exposures of