An early Eocene fish fauna from the Bitter Creek area of the Wasatch Formation of southwestern Wyoming, U.S.A.

ABSTRACT

Early Eocene fluvial ichthyofaunas of Wyoming are relatively poorly known compared with the better-preserved lake deposits of the Green River Formation. We describe the teleost fishes from a single floodplain locality in the main body of the Wasatch Formation that immediately predates the formation of Lake Gosiute, in the Washakie Basin of Wyoming. This assemblage was deposited during the Graybullian substage of the Wasatchian Stage, corresponding to the onset of the rapid climatic warming leading to the Early Eocene Climatic Optimum. In addition to a lepisosteiform and an amiid, the locality has a teleost ichthyofauna comprising Diplomystus (Ellimmichthyiformes), a gonorynchiform probably representing Notogoneus, amblyopsid-like percopsiforms that may represent up to three taxa, and perciforms among which are probably an indeterminate centrarchid and ‘Priscacara.’ The fauna demonstrates that many of the Green River Formation fish taxa were already present in fluvial environments prior to the formation of the Green River lakes, indicating that the subsequent climate warming had little effect on these fishes. Some of the elements recognized here as probably representing Notogoneus were previously recovered from Late Cretaceous deposits from Utah to Alberta, suggesting that this gonorynchid was wide-ranging in North American fluvial environments since Mesozoic times, as were several other taxa identified here. Furthermore, the ichthyofauna indicates that the depositional environment was well vegetated and well oxygenated. These waters were shallow, with gentle flow strengths, which, together with the high oxygen content, suggests that the sediments of the locality were deposited in small ponds connected to an active river system.

Citation for this article: Divay, J. D., and A. M. Murray. 2016. An early Eocene fish fauna from the Bitter Creek area of the Wasatch Formation of southwestern Wyoming, U.S.A. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2016.1196211.

ACKNOWLEDGMENTS

We thank P. Holroyd (UCMP) for lending the fossil material and giving us permission to work on it as well as for assistance with locality information, for which we also thank K. Padian (UCMP). We thank K. Seymour (ROM), S. Laframboise (CMN), and D. Nelson (UMMZ) for lending comparative material, and G. Arratia and A. Bentley (KU) for lending additional comparative material (loan to J. Liu), J. Liu (University of Alberta) for granting access to that material, and H. Stewart (University of Alberta) for her assistance with the coating of fossil material in ammonium chloride. Helpful comments on an earlier version of the manuscript were provided by J. Anderson (University of Calgary), as well as M. Gingras, H. Proctor, and M. Wilson (University of Alberta) and D. Brinkman (RTMP). Further helpful comments on the manuscript were provided by editor C. Underwood and reviewers T. Cook (Penn State Behrend) and D. Brinkman, whom we also thank for granting access to additional comparative material.