Early Chadronian (late Eocene) rodents from the Flagstaff Rim area, central Wyoming

ABSTRACT

The White River Formation at Flagstaff Rim in central Wyoming is a key sequence for understanding the biochronology and chronostratigraphy of the Chadronian North American Land Mammal Age. The lower part of this section represents early Chadronian time, an interval whose fauna has not been well known. From these early Chadronian levels 15 species of rodents are discussed and/or described. Of these, three are new species, all belonging to the Eomyidae: Namatomys erythrus, Metanoiamys paradoxus, Cristadjidaumo skinneri. These rodent assemblages add substantially to our knowledge of early Chadronian faunas, and show successional changes in the rodent taxa from the earliest Chadronian through middle Chadronian.

ACKNOWLEDGMENTS

The rodent specimens described in this paper were collected by Emry's field parties over several summers during the 1970s. During those years, a large amount of sediment from each of the three sites (many tons altogether) were hauled to the North Platte River, where it could be soaked and washed through screens. Assisting in this process were A. Myrick, L. Glenn, S. Sweda, F. Grady, D. Chaney, M. and K. Cohen, J. Flynn, N. David, E. Hunter, L. Holmes, and J. Emry. The coarser fraction of the resulting concentrate was sorted in the field, mainly by those listed above. The much larger volume of finer concentrate was sorted in the VP Preparation Laboratory at the USNM, principally by F. Grady and D. Chaney, who devised a method of separating the teeth from the matrix with heavy liquids, taking advantage of the different densities of the fossil teeth and the sediment particles. Our appreciation goes to all of those mentioned for their hard work at the beginning of the process, and for their patience with the tedium of sorting. We thank S. Jabo of the VP Preparation Laboratory who assisted in making casts of many of the specimens, which were necessary for photography. For improvements to the manuscript resulting from their careful critical reviews, we thank J. Eaton and a second reviewer who opted not to remain anonymous but nevertheless remained so.

Handling editor: Guillermo Rougier