Bat
There are few fossilized remains of bats, as bats are terrestrial and light-boned. An Eocene bat, Onychonycteris, was found in the 52-million-year-old Green River Formation in Wyoming, United States, in 2003. It could fly, but the well-preserved skeleton showed the cochlea of the inner ear could not achieve the great hearing ability of modern bats. This was evidence that flight in bats developed before echolocation. The team said it lacked ear and throat features not only of echolocating bats today, but also in other known fossil species. Fossil remains of other Eocene bats, Icaronycteris, Archaeonycteris, Palaeochiropteryx, Hassianycteris and Australonycteris all show a similar mixture of basal and derived traits, as expected by mosaic evolution.