Ancient ‘Clawed Bat’ Reveals Clues to Flying Mammal’s Evolution

Onychonycteris bat

The rare and delicate but perfectly preserved bones of a primordial bat found in Wyoming are offering up new clues to the evolution of the flying mammals, and to at least one chapter in the evolution of flight itself.

Onychonycteris-finneyi
An artist’s rendering depicts Onychonycteris finneyi, the most basal known bat, in flight. [(C) Loana Riboli]
Though first discovered a decade ago in the shale of southwestern Wyoming, the nearly complete fossilized remains of a 52-million-year-old bat, the most primitive ever found, have gotten attention mostly for what they don’t have.

While many modern bats have structures in their ears that allow them to use echolocation, the ancient species, dubbed Onychonycteris finneyi, had none, suggesting that bats’ ability to fly came long before its adaptation for using sound to navigate.

Now paleontologists have returned their attention to the rest of the fossil skeleton, to determine what more can be gleaned about bats’ evolutionary history.

“For some time now we’ve been trying to figure out what can be learned about how bats evolved flight,” writes Berkeley paleontologist Kevin Padian in a statement to Western Digs.

“The earliest fossil bats, from the Early Eocene (about 55 million years ago) are already fully-fledged, but they have some features that are somewhat different from today’s bats.”

Chief among them, he notes: Unlike today’s bats, which only have one claw on each wing, this ancient ancestor carried a whole complement of giant claws, one on each finger and toe.

O. finneyi had “unusually large and robust claws,” he writes, suggesting that it was particularly well suited to climbing, especially on surfaces like tree trunks, as well as possibly hanging upside-down, just like modern bats.

“But they probably didn’t roost on the ceilings of caves, because their claws don’t seem delicate enough to fasten the animal to tiny cracks and crevices,” Padian says. “Also, we have no evidence that the first bats roosted in large colonies on cave ceilings.”

Instead, he and colleague Ken Dial of the University of Montana suggest that the early bats’ forebears lived in trees, and their huge claws were testament to their ancestors’ arboreal past.

Onychonycteris-finneyi-fossil
Two fossils of Onychonycteris finneyi were discovered in the Green River Formation of Wyoming in 2003.

As for their ability to fly, the experts note that O. finneyi had smaller wings than modern bats, but it was capable of true, powered flight — by flapping its wings instead of gliding.

And, they add, the animal’s hip bones had already developed the crucial ability to splay the legs out to the sides, instead of in front, allowing it to adopt its flat, sleek flying posture. [Learn about another ancient flyer recently discovered in the same fossil formation: “Extinct Tropical Bird Discovered in Wyoming“]

While the fossil record remains mum on exactly when and how these mammals began to fly, the duo speculates that the predecessors of O. finneyi were rudimentary, but true, flyers who made their lives in the trees and rock faces of Eocene Wyoming.

“The evidence suggests that the ancestors of bats could climb and descend vertical surfaces using robust claws,” Padian writes. “They may have jumped from heights to escape predators or to seek food on the ground, and they may even have tried to catch flying insects as they jumped.”

Padian and Dial presented their research today at the annual meeting of the Society of Vertebrate Paleontology in Los Angeles, California.

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