Oldest known bat skeletons shed light on the evolution of flying mammals

WASHINGTON, April 13 (Reuters) – The two oldest known fossil bat skeletons, discovered in southwest Wyoming and dating back at least 52 million years, provide insight into the early evolution of these flying mammals – today represented by more than 1,400 species.

The fossils, described in a new study, are of a previously unknown species called Icaronycteris gunnelli which is closely related to two other species known from slightly younger fossils from the same region, which in Eocene times was a humid, subtropical ecosystem centered on a freshwater lake.

“This bat was not much different from the insectivorous bats that fly today,” said paleontologist Tim Rietbergen of the Naturalis Biodiversity Center in the Netherlands, lead author of the study published this week in the journal PLOS ONE.

“If she folded her wings next to her body, she would easily fit into your hand. Her wings were relatively short and wide, reflecting a more buoyant style of flight. The dentition (her teeth) clearly shows that they were ‘an insectivorous bat was also most likely an echolocating bat,’ Rietbergen added. Echolocation is a common form of sonar in bats, used for navigation and hunting.

Its teeth possessed sharp cusps and ridges for slicing through the exoskeleton of insects and lacked the rounded grinding surfaces useful for eating fruit.

What’s remarkable about these two fossils – one discovered in 2017 and the other originally unearthed in 1994 and only now recognized as a new species – is how they show that bats early in their history already possessed many traits seen in modern species.

“Bats have roughly resembled bats since they first appeared as complete skeletons in the fossil record,” said the Arizona State University paleontologist and study co-author Matt Jones.

“Icaronycteris gunnelli is a bit different from modern bats – it has longer legs, and its arm bones are a bit different in length. The most remarkable thing is that it retained a claw on its index finger. Some other fossil species in the world this time around, I still have that claw, but it’s been lost in most living bats,” Jones added.

This species was closely related to two other bat species whose fossils had previously been found in the same location – Icaronycteris index and Onychonycteris finneyi. This indicates that there was greater species diversity in the early history of bats than previously thought.

The fossils represent the oldest known bat skeletons – both very complete and well preserved. The only older bat fossils are isolated teeth and jaw fragments from places such as Portugal and China, dating to around 55 to 56 million years ago.

“The early evolutionary history of bats is unclear and we don’t have answers to many questions,” Rietbergen said.

The fact that these oldest known skeletal specimens are clearly fully formed bats suggests that the first bats appeared millions of years earlier.

“They probably evolved during the Paleocene epoch, the 10 million year gap between the end of the Mesozoic era and the Eocene epoch,” Jones said, describing a period of incredible evolutionary experimentation then. that mammals were becoming the dominant land animals following the asteroid impact that doomed the dinosaurs 66 million years ago.

Only two other groups of vertebrates achieved powered flight – flying reptiles called pterosaurs and birds, both of which appeared long before bats. The asteroid knocked out the pterosaurs.

Scientists are still trying to determine which mammals were the ancestors of bats.

“We think bats probably evolved from a small, arboreal insectivorous mammal,” Jones said. “But there are a number of enigmatic fossil insects from when bats would have evolved and it’s unclear which, if any, are related to bats.”

Reporting by Will Dunham, editing by Rosalba O’Brien

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