When: Eocene (all known fossils from a deposit 52.5 million years old)
Where: Wyoming, USA
What: Onychonycteris is the most basal bat currently known. It differs from living bats in having claws on all five fingers, whereas living bats have lost them. This form also has relatively shorter arms and fingers, as well as longer legs and tail than any other bat, fossil or extant. Onychonycteris was an extremely important find, as allowed us to answer a long standing question about bat evolution: Which came first, flight or echolocation? This taxon was capable of flight, and detailed examination of the cranium revealed that it could not echolocate. Thus, bats took to the skies before they developed a system for seeing with their ears.
This amazing fossil is from the Green River fossil lagerstatten in southwestern Wyoming, and is one of two known complete specimens. This example is not the holotype (the specimen which bears the name) as while it looks absolutely gorgeous, the second specimen was arranged on the rock slab in such a way more of the skull could be studied. Additionally, this specimen was actually in the hands of a private collector, and thus not fully available to science. That is until the specimen was mailed, unannounced, to Dr. Nancy Simmons at the American Museum of Natural History, New York. She was working on publishing this taxon at the time, and the private collector had been informed of this, so the family sent the specimen to allow her the best examination possible. That was one awesome package to open, believe me!