Scientists Fill Blanks on Bat Family Tree

January 27, 2005

Although roughly one in five of all mammal species is a bat, the winged animal has long been an enigma to scientists.

Despite what Nancy B. Simmons, a scientist at the American Museum of Natural History, characterizes as a "prominent position among mammals," the evolutionary history of bats is largely unknown. Something like 60 percent of the bat's fossil record is still missing.

"With birds we have some great intermediate fossils," said Mark Springer, a biologist at the University of California, Riverside. "With bats it's a lot more of a guess."

Springer is a co-author of a study that fills in some of the blanks in the bat family tree, published in the January 28 issue of the journal Science.

Exploiting the Eocene

The researchers compared genetic sequences from each modern-day bat family in order to reconstruct the evolutionary relationships among small bats (microbats), which use sound waves to find their prey (a process called echolocation), and big bats (megabats), which generally don't.

Microbats are the vast majority of bats and are found all over the world (except for the polar regions). Megabats are found in the tropics where they are sometimes called flying foxes.

The researchers also used fossils to trace the geographic origins of the major bat lineages.

Around 65 million years ago, a mass extinction event occurred, possibly caused by an asteroid collision with the Earth or particularly heavy volcanic activity. Best known for wiping out the dinosaurs, the extinction event elmininated roughly 75 percent of all plants and animals on Earth. One of the survivors was likely a creature that evolved into modern-day bats.

Although the fossil record is notably lacking, scientists believe that bats fully capable of flight and echolocation, or locating prey and other objects through sound waves, emerged during the geologic time period known as the Eocene (about 50 million years ago), probably in North America. This occurred at a time when the planet's temperature had increased by several degrees, and plant and insect diversity was at a peak.

"Bats are a spectacular group of mammals, with a combination of two remarkable specializations that you don't see in any other land mammals: flight and echolocation," Springer said.

Scientists speculate that bats diversified rapidly in response to these environmental changes which created an ecological niche that could be exploited.

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