28. New Earliest Wasatchian Mammalian Fauna from the Eocene of Northwestern Wyoming: Composition and Diversity in a Rarely Sampled High-Floodplain Assemblage

Author(s): Philip D. Gingerich



A new earliest Wasatchian mammalian fauna is described from twenty localites in the Bighorn and Clarks Fork basins of northwestern Wyoming. These localities are in greenish gray sandstones and brightly colored mudstones within the Clarkforkian-Wasatchian boundary sandstone complex, or in brightly colored mudstones correlative with and lateral to the boundary sandstone. The fauna represents a new basal zone of the Wasatchian, here called zone Wa0
Thirty-five mammalian genera and 41 mammalian species are known from zone Wa0. Three genera and ten species are new. The Wa0 fauna includes the earliest North American records of Artiodactyla, hyaenodontid Creodonta, Perissodactyla, and true Primates, but the Wa0 fauna is dominated by hyopsodontids and phenacodontids, and it is compositionally intermediate between those of the preceding Clarkforkian land-mammal age and succeeding Wasatchian land-mammal age. Indices of diversity are high, and the pattern of rank abundance of species fits a model of biotic dependence. High diversity and biotic dependence are characteristics of Wasatchian but not Clarkforkian faunas. The Wa0 fauna includes eleven small species with larger Clarkforkian and/or Wasatchian congeners. All of the small species appear in the Wa0 fauna without Clarkforkian precursors intermediate in size. The depositional setting of Wa0 mammals and associated fauna can be used to test the idea that a sudden appearance of small forms is due to rapid evolution in situ. (Go to the link and see more of this paper.)

Publication Information:

Publisher: University of Michigan

Month of Publication: November

Year of Publication: 1989

Location: Ann Arbor, MI

Volume Number: 28

# of Pages: 97