A new short-legged landbird from the early Eocene of Wyoming and contemporaneous European sites

Fluvioviridavis platyrhamphus, a new genus and species of short-legged land birds from the Lower Eocene Green River Formation (Wyoming, USA) is describ ed. The taxon is known from a single, nearly complete and slightly dissocia ted skeleton which was made the paratype of the putative oilbird Prefica ni vea Olson, 1987 (Steatornithidae, Caprimulgiformes). Apart from the greatly abbreviated tarsometatarsus, Fluvioviridavis especially corresponds to rec ent 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 diff ers in the much narrower proximal end of the humerus. At present, no derive d character convincingly supports a classification of F platyrhamphus into any of the higher avian taxa. The species is here classified 'order and fam ily incertae sedis'. An isolated skull from the Middle Eocene of Messel (He ssen, Germany) is tentatively assigned to ?Fluvioviridavis sp., and associa ted bones from the Lower Eocene London Clay of Walton-on-the-Naze (Essex, E ngland) might also be related to the genus Fluvioviridavis.