Oldest bat skeletons ever found described from Wyoming fossils

Newswise —

A groundbreaking discovery has been made by scientists who have identified a previously unknown species of bat by analyzing the oldest bat skeletons ever found. The study, conducted by a team of researchers from the American Museum of Natural History and Naturalis Biodiversity Center in the Netherlands, sheds light on the evolutionary history of bats, suggesting that they rapidly diversified on different continents around 52 million years ago. Published in the prestigious journal PLOS ONE, this study provides valuable insights into the ancient world of bats and their global distribution during this pivotal time period.

Bats, with over 1,460 living species, inhabit almost every corner of the globe, except for polar regions and a handful of isolated islands. However, in the extraordinary Green River Formation of Wyoming, which contains a rich deposit of fossils from the early Eocene period, researchers have discovered more than 30 bat fossils over the past six decades. Surprisingly, all of these fossils were initially believed to belong to just two known species. However, recent findings have revealed the existence of a previously unknown species among these fossils, challenging the previous understanding of bat diversity in this ancient ecosystem.

Nancy Simmons, co-author of the study and curator-in-charge of the Department of Mammalogy at the American Museum of Natural History, pointed out that bats from the Eocene epoch have been documented in the Green River Formation since the 1960s. However, for many years, the majority of the specimens were categorized as belonging to a single species, Icaronycteris index. It was only around two decades ago that a second bat species from a different genus was identified, as described by Simmons herself in 2008. She further revealed that she had long suspected the presence of additional bat species in the Green River Formation, based on her extensive research in the field.

In recent years, scientists from the Naturalis Biodiversity Center started looking closely at Icaronycteris index by collecting measurements and other data from museum specimens.

Tim Rietbergen, an evolutionary biologist at the Naturalis Biodiversity Center, shared that the paleontologists have amassed a significant number of bat specimens that were initially identified as Icaronycteris index. However, their extensive collection led them to question whether there might actually be multiple species among these specimens. Their curiosity was further piqued when they came across a new skeleton that captured their attention, prompting them to shift their focus and investigate the possibility of previously unrecognized bat species in the Green River Formation. This discovery has opened up new avenues for research and has the potential to expand our understanding of bat diversity during the Eocene epoch.

The discovery of the new bat species was made possible by an exceptionally well-preserved skeleton that was collected by a private collector in 2017 and subsequently acquired by the Museum. Upon comparing the fossil with Tim Rietbergen's extensive dataset, it became evident that it represented a distinct species. Intriguingly, a second fossil skeleton, which had been found in the same quarry back in 1994 and was housed in the collections of the Royal Ontario Museum, was also identified as belonging to the same new species. In honor of the late Gregg Gunnell, a paleontologist from Duke University who made significant contributions to the understanding of fossil bats and evolution, the researchers bestowed the name Icaronycteris gunnelli on this newly identified species. This recognition is a fitting tribute to Gunnell's important work in the field of paleontology

Although there are fossil bat teeth from Asia that are slightly older, the two I. gunnelli fossils represent the oldest bat skeletons ever found.

While there are fossilized bat teeth from Asia that are slightly older, the two well-preserved skeletons of Icaronycteris gunnelli discovered in the Green River Formation represent the oldest bat skeletons ever found. These fossils provide invaluable insights into the early evolution and diversity of bats during the Eocene epoch, and their remarkable preservation offers a unique window into the anatomy and biology of these ancient mammals. The findings from the study shed new light on the evolutionary history of bats and contribute to our understanding of their remarkable adaptability and success as a group of mammals.

While the I. gunnelli skeletons are the oldest bat fossils from this site, they are not the most primitive, supporting the idea that Green River bats evolved separately from other Eocene bats around the world.

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

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