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| The oldest bat fossil found to date would have flown around what is now the US state of Wyoming 52 million years ago. But how did it find food without echolocation? (Source: Royal Ontario Museum) |
The oldest bat skeletons in the world have been identified as a new species, helping scientists fill in the spotty fossil record of these flying mammals and providing new clues about how they evolved. Both skeletons were recovered from an ancient lakebed in southwestern Wyoming, a site that preserves an entire subtropical lake ecosystem and surrounding forest from about 52 million years ago.
The newly discovered bat, Icaronycteris gunnelli, weighed only about 25 grams, roughly as much as five marbles. It had already evolved the ability to fly and likely had developed the capacity to echolocate. The small bat probably lived in the trees surrounding the lake, flying over the water to hunt insects, says Tim Rietbergen, an evolutionary biologist at the Naturalis Biodiversity Center in the Netherlands and lead author of the study describing the species in the journal PLOS ONE.
Today bats are among the most successful animals on the planet, with more than 1,400 species accounting for one-fifth of all mammal species. They live on every continent except Antarctica, and they are often critical to ecological stability, providing key functions such as pollination, seed dispersal, and insect population management.
Despite the ubiquitousness of bats, scientists know very little about their origins. The skeletons from Fossil Lake, the name of the preserved lakebed in Wyoming, date to the early Eocene epoch. At that time, global temperatures were on the rise and mammals, insects, and flowering plants were rapidly spreading and diversifying. These bats look remarkably similar to modern bats, with elongated fingers to hold wing membranes.
“The thought is that … bats originated from some sort of small, insectivorous mammals that were probably arboreal,” says Matthew Jones, a paleontologist at Arizona State University and one of the authors of the study. “But there’s a lot of those,” he adds, pointing out that we don’t know which ones may be related to bats. “Most of them are only known from isolated teeth and jaw fragments.”
After bats appear in the fossil record, they quickly spread around the world. The most ancient bat teeth and jaw bones found so far are roughly 55 million years old. Incomplete specimens from Portugal and China predate the newly described skeletons by a few million years. Scientists don’t know where bats first appeared, though it was likely in Europe, Asia, or North America before the animals spread to the Southern Hemisphere.
“It’s kind of a mystery,” says Alexa Sadier, an evolutionary biologist at the University of California, Los Angeles, who was not involved in the new study. “We don’t have any transitional forms.”
Rietbergen first saw one of the skeletons of Icaronycteris gunnelli in 2017 when he was scrolling through Facebook. “I was like, hmm, this looks a little bit different,” he says.
After asking for some measurements of the fossil, which had been found at a private quarry and was listed for sale, he reached out to Nancy Simmons, a bat expert at the American Museum of Natural History. She agreed with him that it looked like a new species, and AMNH bought the fossil for its collections.
In addition to analyzing the new fossil, the study team reexamined bat skeletons that were already in museum collections. They found another fossil of I. gunnelli that had been acquired by the Royal Ontario Museum in 2002 and was originally classified as the related species.
The two skeletons look similar to modern bats, but there are subtle differences. “One thing that stood out for me in the first place,” Rietbergen says, “was the robustness of the bones, especially the hind limbs.”
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