Researchers Discover ‘Missing Link’ in Bat Evolution

Specimen on display at the ROM demonstrates that bats flew before they could echolocate

The discovery of a remarkably well-preserved fossil of the most primitive bat species known to date demonstrates that the animals evolved the ability to fly before they could echolocate. The new species, named Onychonycteris finneyi, was unearthed in 2003 in southwestern Wyoming. It is described in a study featured on the cover of the February 14 issue of the journal Nature, co-authored by Royal Ontario Museum (ROM) assistant curator of Vertebrate Palaeontology Dr. Kevin Seymour, and researchers from the United States and Germany. A cast of one of the two known specimens is on permanent display in the new Gallery of the Age of Mammals at the ROM.

“Up until now, all fossil bats looked pretty much like living bats” said Dr. Seymour. “Now, for the first time, we have a glimpse of what an ancestral bat looked like, and it surprised us.”

Bats represent one of the largest and most diverse orders of mammals, accounting for one-fifth of all living mammal species. Despite the fact that bats are so widespread and include a fossil record that extends over more than 50 million years, the evolutionary timing and development of both echolocation (sonar) and flapping flight has been widely debated. The well preserved condition of the new fossil permitted the scientists to take an unprecedented look at the most primitive known member of the order Chiroptera.

"When we first saw it, we knew it was special,” said lead author Nancy Simmons, Chair of the Division of Vertebrate Zoology and Curator at the American Museum of Natural History (AMNH) in New York. “It’s clearly a bat, but unlike any previously known. In many respects it is a missing link between bats and their non-flying ancestors.”

Dating the rock formation in which the fossil was found put its age at 52 million years. Onychonycteris was not the only bat alive at the time---fossils of Icaronycteris, a more modern bat that could echolocate, are found in the same formations, and one of these bats is also on display with Onychonycteris at the ROM.

A careful examination of Onychonycteris's physical characteristics revealed several surprising features. For example, it has claws on all five of its fingers, whereas modern bats have, at most, claws on only two digits of each hand. The limb proportions of Onychonycteris are also different from all other bats—the hind legs are longer and the forearm shorter—and more similar to those of climbing mammals that hang under branches, such as sloths and gibbons.

The fossil's limb form and the appearance of claws on all the fingers suggest that Onychonycteris may have been a skilled climber. However, long fingers, a keeled breastbone and other features indicate that Onychonycteris could fly under its own power like modern bats. It had short, broad wings, which suggest that it probably could not fly as far or as fast as most bats that evolved later. Instead of flapping its wings continuously while flying it may have alternated flapping and gliding while in the air. Onychonycteris's teeth indicate that its diet consisted primarily of insects, just like that of most living bats. However, unlike living bats that echolocate, Onychonycteris lacks the ear and throat features present in all living echolocating bats, and even present in other fossil bats such as Icaronycteris.

“There has been much debate about how bats evolved, because there were no specimens to address this issue” said Dr. Seymour. “Now, the combination of features seen in this species finally gives us an answer: that flying evolved first and echolocation must have evolved later.”

Onychonycteris finneyi was named for Bonnie Finney, the excavator who found the specimen and first recognized its importance. Co-authors on the study include Kevin Seymour of the ROM, Jörg Habersetzer of the Senckenberg Research Institute in Germany and Gregg F. Gunnell of the University of Michigan Museum of Paleontology in Ann Arbor, Michigan. Funding for the work was provided by the U.S. National Science Foundation and Deutsche Forschungsgemeinschaft.

Gallery of the Age of Mammals:
The Gallery of the Age of Mammals, located on Level 2 in the west Crystal, opened in December 2007 and displays specimens from the Cenozoic Era (from 65 million years ago to the present). The 5,000 sq. ft. (465 sq. metres) Gallery presents more than 400 fossils, with 30 full mammal skeletons (including four bats), representing the diversity of life during the Age of Mammals that followed the extinction of the dinosaurs. The Gallery is also home to more than 100 non-mammal specimens representing other life forms of the Period.