In 2005, scientists discovered a tiny bat in the Andes Mountains of Ecuador. This bat, Anoura fistulata, has the longest tongue relative to body length of all the mammals. Longer than its entire body, the tongue of the tube-lipped nectar bat--which it uses to lap nectar from long-tubed flowers--is just one example of how bats have evolved over time to become some of the most successful mammals on earth.
Bats are an incredible success story: of the 5,400 known living species of mammals, more than 1,000 are bats. As a group, bats hold several titles among the mammals. They are the only mammals that can truly fly--an ability that arose separately in birds, insects and some extinct reptiles, but has evolved only once in mammals some 50 million years ago, when bats took to the air.
The long-fingered wings that bats use for flight evolved from flightless ancestors with short fingers. Biologist Karen Sears and her colleagues recently found that during early development, bat and mice fingers grow at the same rate. But about halfway through gestation, the bat fingers start growing much faster. Researchers believe a single gene may be responsible for the shift. So, a seemingly giant leap in evolution from fingers to wings may be smaller than first thought.
Perhaps most well-known for their uncanny ability to avoid flying into things in the dark, many bats use sound to navigate at night. By sending out high-frequency squeaks and listening to the resulting echoes, bats can fly fast and locate food, even in the total darkness of a nighttime forest. This ability, which also evolved independently in some mammals including dolphins, toothed whales, and shrews, is called echolocation.
As much as we know about bats and how they get around, the answer to a long-time bat mystery comes from Wyoming, circa 52 million years ago. Did bats first fly, or echolocate--that is, use sound to navigate and feed at night?
The fossil bat, Onychonycteris finneyi, provides clear evidence that flying came first. The skull and bones of this fossil lack known adaptations for echolocation, but its skeleton, including its already elongated finger bones, reveals that it had wings and could definitely fly.
- The smallest mammal alive today is the bumblebee bat. Found only in Thailand and Myanmar, the bumblebee bat is no bigger than a bee and weighs only about as much as a dime. The tiny bat beats its wings so fast that it can hover in place like a hummingbird and is so rare that it was unknown to science until 1974.
- Some bats can walk. Vampire bats, for instance, often crawl undetected onto the bodies of their sleeping prey to bite them and sip their blood.
- Researchers believe that Anoura fistulata, the nectar bat from Ecuador, is the only bat that can pollinate the flowering plant, Centropogon nigricans.
- The Mexican free-tailed bat is the fastest flying mammal with a top speed of 60 miles per hour (97 kph).
The evolutionary history of bats has not been completely resolved. Nancy Simmons of the American Museum of Natural History and other scientists are gradually unearthing their early evolutionary origins. Research suggests that flying bats might have evolved from a wingless, four-limbed ancestor. The proportions and anatomy of the spectacularly complete fossil bat, Onychonycteris finneyi, from Wyoming, reveals clues about the transition.
- Claws on five fingers of each hand--a primitive mammal characteristic; modern bats lost several claws during evolution
- Shorter front limbs than modern bats
- Longer rear limbs than modern bats
- Ratio of forelimbs' length to hindlimbs suggests that this specimen was transitional between non-flying mammals and bats
- Very long fingers, like modern bats