Oldest known bat skeletons shed light on early mammalian flight

From humid Amazonian caves to tree cavities and rock crevices in Wyoming, bats make their homes all around the world. A new study published today in PLOS ONE describes two of the oldest known bat fossils, which may help scientists learn how these mammals evolved the ability to fly and dispersed across oceans and continents.

The relatively small bat skeletons, approximately 1.5 inches in length, were found in a fossil bed near Kemmerer, Wyoming. They were excavated from a fossil-rich geologic formation of ancient swamps and lakes from an era called the Eocene, dating to around 50 million years ago. Called the Green River Formation, the site spans parts of Wyoming, Utah, and Colorado. Based on the age of the sediment layers surrounding the fossils, researchers estimate the bats to be around 53 million years old, making them the oldest bat fossils on record. Bats are thought to have first evolved from nonflying mammals around this time.

Next, paleontologists compared the fossils with other known species and concluded they belonged to a group of extinct bats called Icaronycteris. The newly found bats had a collection of traits—including the presence of claws on the wing's first and second digit, and relatively short forearms and broad wings—that differentiated it from other Eocene bats. The researchers pronounced it a new species, Icaronycteris gunnelli, after the late Duke University paleontologist Gregg Gunnell, a major contributor to the study of bat evolution.