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Onychonycteris finneyi

Onychonycteris is the more primitive of the two oldest known monospecific genera of bat. It lived in Wyoming area in the Early Eocene period, 52.5 million years ago.

Two specimens 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). Onychonycteris occurs alongside Icaronycteris index, previously thought to be the most primitive known bat species (2). Onychonycteris was the only bat to have claws on all five fingers, as opposed to two or three in all other known species (3); Onychonycteris means "clawed bat". The specific epithet is a tribute to the fossil prospector and preparator who discovered it, Bonnie Finney (1)

O. finneyi is the strongest evidence in the debate on whether bats developed echolocation before or after they evolved the ability to fly. O. finneyi had well-developed wings and could fly. It lacked the enlarged cochlea of all extant echolocating bats, so more closely resembles the Old World fruit bats that do not echolocate (1). This indicates that early bats could fly before they could echolocate (4). Evaluation of the Onychonycteris fossil in 2010 provided evidence for other bone structures indicative of laryngeal echolocation, so O. finneyi may have been able to echolocate after all (5). As the fossil itself has been flattened, there is uncertainty about both conclusions (6). It is unknown if Onychonycteris had the large eyes of most nocturnal animals as no specimens have been found with intact eye sockets (1). If it lacked enlarged eyes, it may have been diurnal, solving the problem of how primitive bats evolved flight without the ability to navigate at night using echolocation.


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