Extinct Walking Bat Found; Upends Evolutionary Theory
Carolyn Barry in Sydney, Australia
for National Geographic News
|August 4, 2009|
A walking bat in New Zealand took its marching orders from an ancestor, a new fossil-bat discovery reveals.
Scientists had long thought that the lesser short-tailed bat evolved its walking preference independently.
Since the bat's native habitat lacks predators researchers reasoned that—much like flightless birds on isolated islands—the bat had adapted to its safer surroundings in part by walking.
But the discovery of fossils of a now extinct walking bat in northwestern Queensland, Australia, suggests that the modern-day bats descended from 20-million-year-old Australian relatives.
"We were amazed to find they were virtually identical to the bats in New Zealand today," said study leader Sue Hand, a paleontologist at the University of New South Wales in Sydney.
(Related: "Six New Prehistoric Bat Species Discovered in Egypt.")
The fossil bat had a similar groove in its elbow as its modern counterpart. This supports a specialized muscular system that allows bats to launch from the ground, where they spend about 40 percent of their time.
Unlike its modern relatives, the ancient bats had plenty of predators, Hand said, including marsupial lions and carnivorous kangaroos.
But the quick little bats, measuring up to three inches (up to eight centimeters) long, would have easily escaped capture.
"They're very agile on the ground, quick to fly, and reasonably aggressive," Hand said.
The New Zealand bats "were in a perfectly good position to exploit a predator-free niche," she added.
(See a Australia and New Zealand map.)
Gaining the ability to walk and burrow opened up new food opportunities for the mammals, she added.
"Being on the ground allowed it to have an incredibly broad diet—an advantage when things became colder."
About 15 million years ago, when Australia underwent a climatic shift that made the continent cooler and drier, the Australian walking bats seemed to have died off.
Of the 1,100 known present-day bat species, the lesser short-tailed bat and the American common vampire bat are the only two known to walk on the ground.
The vampire bat is still thought to have evolved its walking ability independently, probably because walking allows the bat to chase after injured prey on the ground.
The finding was published July 20 in the journal BMC Evolutionary Biology.
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