On a Wing and an Ear
Nancy Simmons ’81 delves into the mysteries of how and when bats became the flying hunters of the night.
Story by Sally Ann Flecker / Photos by Piotr Redlinski, World Picture News
One of the great pleasures of summer is that sliver of
evening suspended between twilight and dusk when the
deepening sky seems in no hurry to yield to night. That’s the time the
bat comes swooping over our roof. Look up, I tell my kids, and we
watch, transfixed while it sails through the air, wings fluttering as fast as
a baby’s heartbeat. It makes a few figure eights in long elliptical loops
above our houses, darting here and there to snatch an insect in mid-flight.
Then it’s gone, and we’re left, undeniably earthbound, with a
feeling of wonder.
There’s a lot to marvel over when it comes to bats. I didn’t
know that while our bat was putting on its air show, it was figuring
out what was in the environment around it by producing
high frequency sounds—much too high for human ears. That’s
called echolocation. It’s one of two very specialized capabilities
that give bats a big advantage in the mammal world. The other
is flight. For years, evolutionary biologists have been curious to
know which of the two came first. This past year, Nancy
Simmons ’81, in an article in Nature, put the question to rest.
Simmons is curator-in-charge of mammalogy and chair of the vertebrate zoology division at the American Museum of Natural
History in New York City, and an expert on bats. Simmons’ office, which you would never be able to find without a guide, is
the kind of well broken-in, professorial study that would look right at home at many a college. Well, except for the
trophy lion from the museum’s collection looking down from its perch above the fireplace mantel. And the flying fox—one of the larger bats, hovering with spread wings in the airspace
next to Simmons’ computer monitor. And the pickle jars further down on her worktable, each holding a bat—one labeled India, May 1923, the
other Belize 2002—preserved in a murky solution. Then there are the real gems: two recently discovered 52 million-year-
old fossils of a kind of bat never before seen, collected at Wyoming’s Green River geological formation. One is on loan
from a private collector, the other from the Royal Ontario Museum. Each is oddly beautiful and mysterious—delicate, petrified
bones encased in a grainy slab of putty-colored stone that fits comfortably in Simmons’ hand. The extravagantly long hand
and finger bones that once supported its wings dangle like streamers at the end of folded arms. Its rib cage seems swelled
with air, and each bone in its clawed feet seems poised to push off for a flight that never came. The fossils were central to her
work that landed on the cover of Nature. Simmons doesn’t know how much they’re worth. Actually, she clarifies, she’s been
careful not to find out.
Bats weren’t something Simmons knew a lot about when she
accepted a post-doctoral fellowship at the American Museum in
1989, although, she tells me, she had always thought they were
“very cool.” She had spent years studying fossils—her graduate
work focused on a group of Mesozoic mammals that have no
living relatives. When she finished her Ph.D., she thought she
would like to try working on an animal that had, as she puts it,
living relatives and living diversity.
There’s no doubt about bats having living relatives. There
are 1,100 known living species, which means that one in every
five living mammal species is a bat. They live on every continent
except Antarctica, with many congregating in the tropics. When
Simmons did field work in French Guiana a few years back, she
found 76 species of bats, all within a three-kilometer walk from
camp. That may make it sound like it was a piece of cake to find
so many. But Simmons and her team worked hard for that
bounty, placing their traps and nets high and low. They crawled
into wet, mucky roosts, which, in the rainforest, might be in a
hollow log or in the shelter formed by the many buttress roots
of a fallen tree—neither being particularly inviting unless you
have a penchant for brushing up against creepy-crawlies.
That’s not to mention the conditions—nasty, rainy, muddy, with multitudes of mosquitoes, and having to work on little
sleep. Bats are nocturnal. If you’re going to study bats in the field, you have to work at
night. But in order to maximize your catch at night, you work most of the day, too. You
move nets and process samples. Then you grab something to eat and run back out to spend
most of the night picking bats out of nets.
The sheer diversity of the order Chiroptera—from the Greek words for hand and wing—fascinates Simmons.
Give Simmons three minutes and she can paint a pretty good picture for you. Consider differences
in size, for starters. The very smallest, she says, weighs about a gram—less than a penny—as an adult and when its wings are fully open, the span
is around three inches. At the other end of the spectrum is a bat that has a wing span up to six feet.
Most of us think that bats fly around and catch bugs, and
many of them do. There are bats that are specialized for feeding
on beetles, she says, and bats that are specialized for feeding on
moths, and bats specialized for feeding close to the ground, and
still others that fly above the canopy. Some bats listen for the
sounds their quarry makes when hitting a leaf, and then dive in
to catch them. There are bats that snatch fish with their hind
feet and bats that eat mice, lizards, small birds—sometimes even
“We always sort of suspected there were two things that were
key to the evolution of bats that made it possible for them to
diversify the way they did. One of those being flight, obviously,
because it allows them to take advantage of a whole different
part of the eco-world,” says Simmons. “The second is echolocation
because that allows them to access all of the flying insects of
the air, and it also allows them to navigate at night. They can
be nocturnal, flying, aerial insectivores, and take advantage of
this vast set of riches of food stuff available.”
Understanding how—and when—these two bat “superpowers” evolved has eluded evolutionary biologists until now.
Simmons’ primary research interest is evolutionary biology
and the anatomy of organisms—how they are built, how they
got that way, how they are related to one another, and how you
can tell. Most of her work is done with living species of bats.
But because of her training in paleontology, she is also interested
in fossils, which is why the ancient bat fossils—in her hand
now as she shows them to me—were brought to her attention.
Here’s how echolocation works. The bat beams out a high-pitched
call through the mouth, and in some species, through
the nose. When the sound encounters something, it bounces
back. The bat’s specialized hearing allows it not only to detect
the sound, but also process the amount of time it took to bounce back. What that
gives them is kind of a sonogram on the fly, a map of what’s around.
But here’s a twist—not all bats echolocate. One family out of the 19 living families of bats uses vision
rather than echolocation. That’s the Old World fruit bat or flying fox, like the one hanging at Simmons’
desk. They don’t eat insects; they eat fruit and flowers for nectar. Interestingly, they
are less diverse than the other 80 percent of bats who use echolocation.
“How did these features evolve? How did bats become flying mammals? How did they become echolocating mammals?”
Simmons asks. “And, one of the most basic questions is, did these two features evolve together or did one come first?”
Until recently, there were three theories about bat evolution. There’s a flight first hypothesis that suggests bats had a gliding
ancestor. They evolved flight as a means to get around in their environment, and later developed echolocation to help them
better detect the insects they need to eat in abundance.
According to the second hypothesis, which argues for echolocation first, bats were a scrambling, tree-dwelling animal
that used echolocation to detect food sources, and subsequently evolved flight to get around better and to be able to chase after
the insects they detected through echolocation into the air.
In the 1990s, a new discovery showed that the high-intensity echolocation calls take a lot of energy to produce in a stationary
bat. When the bat flies, though, the flight muscles pump the lungs, so there is a savings in energy. This suggested a third theory
of tandem development: If there is no cost for echolocation when the bat is flying, maybe flight and echolocation evolved at
the same time.
All three theories were plausible, says Simmons, and virtually untestable—but here’s where the 52 million-year-old fossils she
is studying come into play. The new bat, which Simmons and her team named Onychonycteris, has characteristics that place it
early in bat evolution. For instance, it has claws on all five fingers, just as its terrestrial ancestors did. And it has the anatomical
features, the exceptionally long fingers, for instance, needed for flight.
Bats that echolocate share three anatomical features. The first
is an enlarged cochlea—the spiral-shaped cavity of the inner ear.
Next is the stylohyal element that connects the base of the skull
to the bones in the throat that support the voicebox muscle. In
bats that echolocate, the stylohyal is long and skinny, with a
paddle at the end to help it attach more firmly to the base of the
skull. Finally, the malleus, the ear ossicle that contacts the eardrum, has a knob on
the end that affects how it vibrates. It’s clear from the specimen that
Onychonycteris had none of these features. Simmons could see there was no way
it could echolocate. Mystery solved—it’s flight first.
Before I leave her office, Simmons shows me a few other bats from the museum’s
collection, which includes around 60,000 bat specimens representing almost every species from
around the world. She shows me fossils, skulls, bones, molars, full skeletons, skins. She
takes a bat out of a display drawer that looks like a little stuffed animal. This one has been prepared so that the banding patterns
on its fur can be studied. As she talks, she strokes its head gently
the way you would a pet. “From the mammal’s basic biological
plan—we’re warm-blooded, we have hair, we give milk, we have
a skeleton inside, we have a basic set of internal organs—you
have things as diverse as bats and whales and horses and cats and
shrews. I just find that amazing,” she says. “I want to understand
as much as I can about the evolution of diversity. And as
we collect more genetic data, more morphological data, and we
actually start to solve some of these problems, it’s just going to
In the scientific world, answers beget more questions. Same
at my house. It’s winter now, and our bat is either hibernating
or has gone some place warmer. “Bats are blind,” my six-yearold
tells me with great authority, adding the definitive, “Dad
said.” He thinks about it for a minute then asks, “If bats are
blind, how can they fly?” His brother picks up the rubbery bat I
brought back for him from the museum’s gift shop. He is five,
so, of course, he flies it like an airplane around the room. Come
spring, when we welcome back our bat, we’re going to find a lot
to talk about.