Two bat fossils recovered from the rocks of southwestern Wyoming have given scientists new clues about early bat evolution. The fossils have been classified as belonging to a new species of ancient bat, Onychonycteris finneyi, which lived about 52 million years ago. The fossils were unearthed in 2003 from Wyoming's Green River Formation, a geologic formation that dates back to the Eocene epoch (58-37 million years ago) and consists of layers of sediment deposited in a chain of intermontane lakes.

The fossils depict a type of bat that possessed well-developed wings capable of flight. But flight was not the only mode of locomotion available to Onychonycteris—a number of characteristics revealed by the fossils hint of an animal well-adapted for climbing. It had claws on all five of its fingers (all other known bats have claws on only two or three fingers on each hand). Additionally, its hind legs were longer and its forelimbs shorter than modern bats.

From an evolutionary perspective though, the most notable characteristic that sets Onychonycteris apart from modern bats and other previously discovered fossil bats is that it lacked the skull and throat structures necessary for echolocation. Thus, Onychonycteris demonstrates that bats were capable of flight before they were able to echolocate.

Nancy Simmons of the American Museum of Natural History in New York, described the species as a sort of 'missing link' in bat evolution. Although other bat species had previously been discovered that date back to the same time period as Onychonycteris, only Onychonycteris lacks the ability to echolocate and as a result is considered to represent a more primitive specimen than previously discovered bat fossils.

Find out more:

• Bats Flew First, Developed Echolocation Later, Fossilized Missing Link Shows (Science Daily)
• Primitive Bats Took to the Wing, but They Didn’t Have That Ping (The New York Times)
• Bat Fossil Solves Evolution Poser (BBC News)
• Researchers Discover ‘Missing Link’ in Bat Evolution (Royal Ontario Museum)
• Green River Formation (UC Berkeley)

Photo © Royal Ontario Museum, reprinted with permission. Cast of one of two Onychonycteris finneyi fossil specimens. The wing digits are well-laid out on the viewers left side, and show the small claws at the tip of each finger.