Eocene Climate Conditions and NorAm Fauna

Climate directly influences Eocene mammal faunal dynamics in North America

1. Michael O. Woodburne (a,1),
2. Gregg F. Gunnell (b)
3. Richard K. Stucky (c)

a. Department of Geology, Museum of Northern Arizona, Flagstaff, AZ 86001
b. Museum of Paleontology, University of Michigan, Ann Arbor, MI 48109
c. Denver Museum of Nature and Science, Denver, CO 80205


1. To whom correspondence should be addressed. E-mail: mikew@npgcable.com



Abstract: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 ([less than]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.

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