Onychonycteris is the more primitive of the three oldest bats known from complete skeletons, having lived in the area that is current day Wyoming during the Eocene period, 52.5 million years ago.

Two specimens of Onychonycteris were found in the Green River Formation in 2003, and placed in a new family when the discovery was published in Nature, in February 2008.

[1] The specific epithet is a tribute to the fossil prospector and preparator who discovered it, Bonnie Finney.

Onychonycteris finneyi was the strongest evidence so far in the debate on whether bats developed echolocation before or after they evolved the ability to fly.

[1] A lack of enlarged eyes would indicate that this species may have been diurnal, solving the problem of how primitive bats evolved flight without the ability to navigate at night using echolocation.