An international team of paleontologists has described a new Early Eocene bat species from the well-preserved fossils — which include the oldest uncrushed skull of a bat yet known — found in cave deposit in France. Named Vielasia sigei, this early bat appears to have been capable of advanced echolocation.
Vielasia sigei helps bridge the gap between archaic bats and the hyperdiverse modern bat radiation of more than 1,460 living species. Image credit: Hand et al., doi: 10.1016/j.cub.2023.09.043.
Vielasia sigei lived in what is now Europe during the Early Eocene epoch, some 50 million years ago.
The fossilized remains of at least 23 individuals of Vielasia sigei were recovered from limestone cave sediments at Vielase, in the Quercy Phosphorites, southwestern France.
The well-preserved fossils include the oldest uncrushed skull of a bat yet known.
“Prior to the discovery of this skull, only fragments or completely flattened skeletons of early bats had existed in the fossil record,” said Professor Sue Hand, a paleontologist at the University of New South Wales.
“We don’t know very much about the beginnings of bats because we don’t have the missing links like we do, say, between dinosaurs and modern birds.”
“The oldest bat fossil is about 57 million years old, and it’s a single tooth from a site in Portugal – that’s all we know about it.”
“The first bats are all just known from fragmentary fossils, mostly teeth.”
“When bats appear in the fossil record a little later, about 52 million years ago, some are wonderfully complete bats, but they’re flattened.”
“While these flattened specimens are beautifully preserved, the fact that they’ve been flattened by layers of rock deposited over millions of years makes it difficult to decide with conviction, the exact positioning of bones in their three-dimensional anatomy.”
“And when it comes to determining whether a fossil is from a species of bat that is already using echolocation, detailed and precise anatomy of the skull is crucial.”
“In modern bats, between the voice box and the ear, there are some bones called the hyoid bones.”
“In all modern bats that echolocate, one of these bones directly contacts the middle ear bones and appears to be involved in transmitting high frequency sound.”
“But in the flattened fossils, while we can see these various bones, there is a question about their precise relationships to each other.”
“This has led to a lot of debate among scientists about whether or not a species used echolocation.”
But in the case of Vielasia sigei, not only is the skull almost entirely intact, but it has been preserved in limestone in its original three-dimensional shape.
“In this particular bat, we can see more directly what’s going on deeper, in the inner ear,” Professor Hand said.
“We took fine measurements of that inner ear bone and compared it with that in the bats that do echolocate today and bats that don’t, and it sits in the middle of the ones that echolocate.”
“Not all bats echolocate. Flying foxes rely on their very good eyesight to navigate and find fruit, without echolocation.”
“Meanwhile, Sydney microbats such as the eastern bentwing bat, Gould’s wattled bat and the chocolate wattled bat, are well known for navigating and catching insects using feedback from the high frequency sound they emit.”
“Vielasia sigei used echolocation with 100% certainty. It’s very convincing that the type of echolocation some of these early bats used was indistinguishable from what many echolocating bats use today, and at 50 million years ago, this is well ahead of whales developing this ability.”
“Prior to this find, we were only really certain that echolocation developed in the modern families of bats.”
“We think some of the characteristics of this bat would have also characterised the last common ancestor for modern bats,” Professor Hand said.
“So it’s exciting, and it is actually going to be an important specimen that people will get a lot of information from and use in their own analyses.”
The findings appear in the journal Current Biology.
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Suzanne J. Hand et al. A 50-million-year-old, three-dimensionally preserved bat skull supports an early origin for modern echolocation. Current Biology, published online October 18, 2023; doi: 10.1016/j.cub.2023.09.043
