The Fossil Lake deposits of the Green River Formation of Wyoming in the United States have produced nearly 30 bat fossils over the last 50 years. However, diversity has thus far been limited to only two bat species. Now, paleontologists have described a new species of the bat genus Icaronycteris based on two skeletons discovered in the American Fossil Quarry northwest of Kemmerer, Wyoming.

Life recontsruction of Palaeochiropteryx bats. Image credit: Obsidian Soul / CC BY-SA 3.0.

With over 1,400 living species, bats are the second most speciose group of mammals.

They are found all over the world with the exception of polar regions and a few remote islands, and are ecologically highly diverse, occupying a wide variety of habitats and ecological niches.

Bats play a vital role in healthy natural ecosystems and additionally provide many ecosystem services important for human economies (e.g. pest control, pollination, seed dispersal).

They are also the only mammals capable of true powered flight, an adaptation that evolved early in the history of the bat lineage.

The earliest confirmed records of bats are from early Eocene deposits.

“Eocene bats have been known from the Green River Formation since the 1960s,” said Dr. Nancy Simmons, a paleontologist at the American Museum of Natural History.

“But interestingly, most specimens that have come out of that formation were identified as representing a single species, Icaronycteris index, up until about 20 years ago, when a second bat species belonging to another genus was discovered.”

“I always suspected that there must be even more species there.”

Icaronycteris gunnelli, holotype. Image credit: Rietbergen et al., doi: 10.1371/journal.pone.0283505.

The newly-identified species, Icaronycteris gunnelli, lived in North America approximately 52 million years ago.

The animal weighed 22-29 grams, similar to the body mass estimates for Icaronycteris index.

“Paleontologists have collected so many bats that have been identified as Icaronycteris index, and we wondered if there were actually multiple species among these specimens,” said Tim Rietbergen, an evolutionary biologist at Naturalis.

“Then we learned about a new skeleton that diverted our attention.”

Two fossilized skeletons of Icaronycteris gunnelli were found in 1994 and 2017 in the American Fossil Quarry of the Green River Formation in Lincoln County, Wyoming.

“The relative stratigraphic position of these fossils indicates that they are the oldest bat skeletons recovered to date anywhere in the world,” the paleontologists said.

Icaronycteris gunnelli, paratype. Image credit: Rietbergen et al., doi: 10.1371/journal.pone.0283505.

Icaronycteris gunnelli is the smallest known bat from the Green River Formation and is distinguished from other Eocene bats by a combination of traits.

“Our phylogenetic analysis of Eocene fossil bats and living species places the new species within the family Icaronycteridae as sister to Icaronycteris index, and additionally indicates that the two Green River archaic bat families (Icaronycteridae and Onychonycteridae) form a clade distinct from known Old World lineages of archaic bats,” the authors said.

“Our analyses found no evidence that Icaronycteris menui from France nor Icaronycteris sigei from India belong to this group; accordingly, we therefore remove them from Icaronycteridae.”

“Taken in sum, our results indicate that Green River bats represent a separate radiation of archaic bats, and provide additional support for the hypothesis of a rapid radiation of bats on multiple continents during the early Eocene.”

Source: sci.news