Fluvioviridavis platyrhamphus, a new genus and species of short-legged landbirds from the Lower Eocene Green River Formation (Wyoming, USA) is described. The taxon is known from a single, nearly complete and slightly dissociated skeleton which was made the paratype of the putative oilbird Prefica nivea Olson, 1987 (Steatornithidae, Caprimulgiformes). Apart from the greatly abbreviated tarsometatarsus, Fluvioviridavis especially corresponds to recent oilbirds in the unusually wide proximal end of the humerus. However, in other features, e.g., the shape of its much longer beak, the Eocene taxon is clearly distinguished from the recent oilbird (Steatornis). In contrast, Prefica nivea agrees with Steatornis in the shape of the mandible but differs in the much narrower proximal end of the humerus. At present, no derived character convincingly supports a classification of F. platyrhamphus into any of the higher avian taxa. The species is here classified order and family incertae sedis. An isolated skull from the Middle Eocene of Messel (Hessen, Germany) is tentatively assigned to ?Fluvioviridavis sp., and associated bones from the Lower Eocene London Clay of Walton-on-the-Naze (Essex, England) might also be related to the genus Fluvioviridavis.

Key words: Fossil birds, Eocene, Fluvioviridavis, Green River Formation, Messel, London Clay.

Gerald Mayr [gmayr@sng.uni-frankfurt.de], Forschungsinstitut Senckenberg, Division of Ornithology, Senckenberganlage 25, D-60325 Frankfurt a.M., Germany; Michael Daniels [nazeman@beeb.net], 118 Dulwich Road, Holland-on-Sea, Clacton-on-Sea, CO15 5LU Essex, England.