"As flying predators capable of capturing prey on the wing, they would have had few competitors for the rich resources of the Eocene night," Simmons wrote in a related commentary.

Microbats and Megabats

Bats display astonishing diversity. "They're one of the most fascinating groups of mammals or vertebrates," Springer said.

Bats come in different body sizes. They have different diets, echolocation strategies, flight styles, and reproductive habits.

Megabats, commonly known in Australia as flying foxes, weigh in at two pounds (one kilogram) and can have wingspans of up to six feet (two meters). Microbats are much smaller, with wingspans of up to five inches (twelve centimeters). The tiniest microbat weighs about as much as a dime.

"Microbats echolocate," Springer said. "They have a highly developed inner ear, which they use the way we would use vision. The megabat relies more on vision, and with a few exceptions, they don't echoclocate."

Flight styles and diet also vary widely. Some species have evolved highly sophisticated skills that allow them to track and catch their meals while flying. Others, like the vampire bat, look for a large, stationary target, like a cow, make a small bite and lick the blood from the wound. Most megabats live in the tropics and are fruit eaters.

"Bats are a very little known group," Springer said. "They're not the kind of animal we see when we're out walking around in nature. But at the same time, they're … a tremendously important group in terms of our habitat—and in terms of [their] adaptation[s], one of the most spectacular."

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SOURCES AND RELATED WEB SITES Organization for Bat Conservation Science