Early Eocene fossil vertebrates from the southwestern Green River Basin, Lincoln and Uinta counties, Wyoming

Seven local faunas (Little Muddy I-VII) of early to middle Eocene age are d escribed from the Little Muddy Creek area in the southwestern Green River B asin. These assemblages were collected from approximately 300 m of interfin gering alluvial and lacustrine deposits in the Wasatch, Green River and Bri dger formations. This is the first time the Wasatchian-Bridgerian boundary has been delineated within the southwestern Green River Basin. A continuous stratigraphic section from the late Wasatchian (Wa7) through the late Brid gerian (Br3) is now known in the southern Green River Basin. The Lostcabini an (Wa7) in the southwestern Green River Basin is recognized by the occurre nce of Lambdotherium and the presence of Meniscotherium and Notharctus nuni enus. The temporal range of Anemorhysis wortmani is extended upward to incl ude the Lostcabinian of the southwestern Green River Basin. The late Gardne rbuttean (Bridgerian Biostratigraphic Zone Br1a) is recognized in the south western Green River Basin by the first appearances of Palaeosyops fontinali s and Hyrachyus. "Bridger A" (Bridgerian Biostratigraphic Zone Br1b) is rec ognized in the southwestern Green River Basin by the first appearances of O rohippus pumilus, Omomys carteri, Leptotomus parvus, and Washakius insignis . Other important records include the earliest occurrences of Tetrapassalus sp. and Parasauromalus. The presence of a new genus and species of crocody lian and a new genus and species of helaletid perissodactyl are documented.