Eonessa is an enigmatic genus of bird possibly belonging to bird order Gruiformes and which consists of the single species Eonessa anaticula. It was first described by Alexander Wetmore in the Journal of Paleontology in May 1938. In his paper, Wetmore erected the Anatidae subfamily Eonessinae, and placed Eonessa as the oldest Anatidae genus in the fossil record. This placement was possibly due to a resemblance to the modern ruddy duck (Oxyura jamaicensis), although Wetmore did not explain his taxonomic placement in the describing paper.