The oldest bat fossils discovered in Wyoming are a previously unknown species

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Two 52-million-year-old bat skeletons discovered in an ancient lakebed in Wyoming are the oldest bat fossils ever found, and reveal a new species.

Tim Rietbergen, an evolutionary biologist at the Naturalis Center for Biodiversity in Leiden, the Netherlands, identified the previously unknown bat species when he began collecting measurements and other data on museum specimens.

“This new research is a step forward in understanding what happened in terms of evolution and diversity in the early days of bats,” he said.

Today, there are more than 1,400 species of bats living throughout the world, with the exception of the polar regions. But how the creatures evolved to become the only mammal capable of powered flight is not well understood.

The bat fossil record is spotty, and the two fossils that Rietbergen identified as a new species were lucky finds: exceptionally well-preserved and revealing the animals’ complete skeletons, including teeth.

“Bat skeletons are small, light and fragile, which is very unfavorable for the fossilization process. They just don’t keep well,” he said.

The newly discovered extinct bat species, Icaronycteris gunnelli, was not much different from bats that fly today. His teeth revealed that he lived on a diet of insects. It was tiny, weighing just 25 grams (0.88 ounces).

“If it folds its wings together with its body, it would easily fit inside your hand. Its wings were relatively short and broad, reflecting a more choppy style of flight,” Rietbergen said.

This particular bat lived when Earth’s climate was warm and humid. The two skeletons Rietbergen studied survived for eons likely because the creatures fell into a lake, putting them out of reach of predators and in an environment more conducive to fossilization. The ancient lake bed is part of Wyoming’s Green River Formation and has produced a number of bat fossils.

One of the two fossils was collected by a private collector in 2017 and purchased by the American Museum of Natural History. The other belonged to the Royal Ontario Museum in Toronto and was found in 1994.

The research was published in the scientific journal PLOS One On Wednesday.