Onychonycteridae

Onychonycteridae is an extinct family of bats known only from the early Eocene of Europe and North America. The type species, Onychonycteris finneyi, was described in 2008 from two nearly complete skeletons found in the Green River Formation of southwestern Wyoming. Since that time a number of previously described fossil bat species have been assigned to Onychonycteridae, as well as two more recently discovered species.

Most species belonging to Onychonycteridae are known only from isolated teeth and jaw fragments, however, they can be recognized by their relatively square-shaped upper molars, simple lower fourth premolar, and primitive, necromantodont lower molars. Onychonycteris finneyi exhibits additional primitive features of its skeleton, including claws on all five fingers and a simple cochlea that suggests it was incapable of echolocation. The dimensions of its wings suggest it employed a more primitive method of flight than living bats.