进化史上最大的成就
achievement the power of flight from 就是飞行的力量
insects to birds to bats tens of 昆虫，鸟和蝙蝠
thousands of species fill our skies what 成千上万的物种翱翔于天空
hundreds of millions of years ago flight 数百万年前
did not exist this is something that 还没有物种能飞
only occurred four times in all of the
evolutionary history on the planet how
did these animals come to seemingly defy
the laws of gravity how did they first
take flight
[Music]
the animal kingdom is composed of
millions of species and the fastest of
all of them the peregrine falcon
reaching speeds more than 200 miles per
hour this bird swoops down for more than
a half a mile in the sky to attack
with lethal precision the peregrines
tremendous speed and success at hunting
can be attributed to one simple trait
the power of flight while humans have
always dreamed of flying evolutionarily
flight has passed us by but incredibly
more than three-quarters of all land
animals can take to the air from
butterflies to birds to beetles and bats
these vastly different organisms have
all evolved the complex mechanism of
getting and staying airborne flight
occurs when an animal has enough lift
and thrust to move its body through the
air and to maintain it in the air but
what forces drove the development of
such a remarkable innovation when did
the first animals take to the air and
how did they develop this ability to
seemingly defy the laws of gravity
the sparks of this extraordinary
evolutionary change can be seen all
around us today insects for millions and
millions of years nothing could fly and
so if small invertebrates was moving
around in the forest and wanted to find
food it had to crawl all the way up to
the top of a tree and get the food and
then go down that tree and up another
tree to get food but then suddenly
something happens the first flying
organisms appear and once flight becomes
part of the game it changes everything
the fossil record shows that insects
light evolve suddenly around 350 million
years ago mutations and natural
selection produced the first species
with wings capable of lifting them into
the air this random evolutionary
accident can now be seen in the anatomy
of more than a million insects their
wings have evolved to be like curved
long helicopter blades and the wing
surfaces are not flat which make them
highly maneuverable in tight spaces so
that they can easily find food and
escape predators insects are very good
at flying they can hover they can fly
quickly they can fly backwards
they can turn very tight turns they can
go very very high and they've taken
advantage of this to fill all the
different nations in the world although
insects would be the first animals to
fly they would not be the last to fly an
animal not only has to get up into the
air
but once there it has to be able to take
in huge amounts of energy and oxygen to
power them through the sky
considering the physical demands it's no
wonder that the heaviest flying animal
today the great bustard weighs in at a
mere 45 pounds if you watch birds of
different sizes especially when they try
to take off from the ground the first
thing we usually notice is that large
birds have trouble getting off the
ground but one of the world's first
flyers would break all the evolutionary
rules about size the first group of
vertebrate Flyers would produce the
largest flying animal of all time a 440
pound pterosaur called Quetzalcoatl is
this is Quetzalcoatl it's the largest
flying animal of all time with a
wingspan of about 35 feet this animal
soared over Western North America when
in full flight its wingspan was equal to
three cars parked bumper-to-bumper
imagine that thing coming at you the
gigantic pterosaur had a huge beat head
the size of a human and when standing on
the ground was taller than a giraffe at
four times the size of any flying animal
today it's an anomaly of evolution
what ecological pressures drove these
enormous animals into the sky and how is
it physically possible weighing hundreds
of pounds it seems unlikely even its
massive wings could have generated
enough force to drive it into the air
pterosaurs live 220 million years ago
and were the first vertebrates to evolve
powered flight their name comes from the
Greek pterosaur Oh
meaning winged lizard unlike birds these
first vertebrate fliers did not have
feathers but skin that stretched from
their pinky fingers to their backs to
form a wing the first vertebrate group
to fly to evolved flight were the
pterosaurs they're closely related to
dinosaurs but not dinosaurs themselves
the world of the pterosaur was a
strikingly different place than today
dinosaurs tower above the canopy while
down below millions of insects buzz
around their feet along with hundreds of
species of reptiles all competing for
resources and food the ability to fly
opened up numerous new ecological
possibilities for pterosaurs one of the
earliest ones was probably the ability
to catch flying insects on the wing so
these guys could fly pursue flying
insects grab them and eat them
pterosaurs also look to oceans and lakes
as a source of food they fly over the
water swooping down for fish being in
the air also gives them a better vantage
point for spotting dead animals to
scavenge
new food resources explain the desire
for wanting to get up into the skies but
just how did these 440 pound behemoth
get there how an animal this big got off
the ground and stayed into the air has
been a puzzle ever since its discovery
Michael Habib is an evolutionary
biologist at Johns Hopkins University he
thinks he solved the mystery of how
these monstrous reptiles conquered
flight in the late 1920s a group of
paleontologists unearthed a pterosaur
skeleton on a dig in Oregon included in
the skeleton was a seemingly ordinary
bone from the wing the bone was
dismissed as insignificant and placed in
a drawer at a museum for more than 80
years but Habib believes this simple
bone from the wing may hold the answer
to these massive creatures taking to the
air the bone in question that was found
is the most important part of the wing
for understanding the plight of
pterosaurs the part that basically
connects the wing itself to the body
toward was the flight most attached when
I talked to the curators of museum about
the pterosaur collection was in fact the
last thing they showed me almost an
afterthought it asked we forgotten it
was there the bone was incredibly well
preserved and Habib sensed he may be
onto something here
in front of him could be the part of the
anatomy that might just explain how an
animal four times larger than anything
else flying on earth could generate
enough force to get up into the air and
stay there Abby wanted to capture
high-tech x-ray images of the interior
of the fossil at the Johns Hopkins
University School of Medicine
the first thing to be noted was
something paleontologists have long
known about the pterosaurs bones they
were hollow hollowness allow supposed to
be very very large that if the diameters
can be very wide makes them very strong
things they put a lot of muscle power on
them and the bone will hold up this bone
however was not completely hollow have
Eve noticed some strange grouse inside
the bone it looked like support beams
similar to flying buttresses on a
Cathedral that keep the walls from
buckling inwards their range in
particular directions in the direction
shows you where the bone needed the most
reinforced where it needed the biggest
push on the inside keep it from
collapsing with this discovery ABI was
able to figure out what this bone was
used for it was used to help launch
pterosaurs like the 440 pound
Quetzalcoatl is off the ground much like
a diver pushing off a springboard
launching it actually very rigorous very
difficult for flying animals in the
sense that they have to get a lot of
speed built up in a very short period of
time
to launch off the ground and into air an
animal has to generate a lot of force
which takes a lot of muscle power in
birds you see this missing the hind legs
because birds actually not the wings
that most get the bird off the ground
extra legs legs give the initial leap
suck them into the air the discovery of
the internal brace system suggests that
these front limbs were strong enough to
push the pterosaur up off the ground and
propel its huge body into the air so
their wings were more than just agents
of flight they were actually front legs
that they used to walk around on and
help them push off and into the air
Habib's discovery may go a long way to
answering some of the lingering debate
about how these large first vertebrate
fliers got airborne but the question
remains why is there nothing this big
flying today the answer may be the size
itself of these animals large animals
need more food to sustain themselves and
in times of environmental distress
catastrophe animals like this this 35
foot wingspan pterosaur would have had a
much harder time feeding itself than a
bird a fraction of its size
their size may have eventually led to
their extinction but a hundred and fifty
million years ago another group of
animals was independently evolving the
ability to fly alongside the pterosaurs
with different flight strategies
naturally selected for their size and
Anatomy interestingly small bird make up
more than half the species of birds in
the world so in the evolution of birds
small birds have arguably been much more
successful than their larger
counterparts the birds inspiration
not the flying pterosaurs but flightless
killers on the ground 150 million years
ago during the mid Jurassic period life
is teeming with new species not only on
the ground but also far above in the sky
to separate evolutions of powered flight
has given rise to millions of species of
insects and pterosaurs have been soaring
high above the canopy for over a hundred
million years but they were no longer
alone a new class of creatures was
evolving independently alongside them
that would take flight to new heights
convergent evolution is a phenomenon
where organisms from two different
ancestries evolved similar
characteristics in response to similar
environmental pressures and the
evolution of flight is an excellent
example of convergent evolution birds
and pterosaurs both evolved similar body
plans in response to the need to fly
more efficiently from pigeon to peacock
eagle to sparrow today there are over
10,000 species of birds on the planet
twice as many as mammals
exactly when they evolved and how they
adapted flight is a 230 million year old
detective story but if you know where to
look there are telltale clues Hey
avi Cohen ironically the answer to how
birds took to the air may lie on the
ground large flightless birds like emus
help trace the origin of avian flight
because it is believed that birds
evolved not from winged pterosaurs
but ground-dwelling dinosaurs this
animal the EMU is one of the closest
things left on earth that might be able
to tell us what non-avian dinosaurs
really looked and acted like for
instance look at the feet of an emu we
see scales on the feet like a reptile
and also three weight-bearing toes like
a non-avian theropod dinosaur theropod
dinosaurs stood upright with hind legs
used for support and movement while
short four limbs were used for grasping
and tearing prey the most famous was the
fearsome t-rex if we were to look at the
foot of a t-rex and put a t-rex foot
next to the foot of his he knew it
seeing many many similarities and only a
few differences
I think the most obvious feature that
birds share with non-avian dinosaurs a
feature they inherited from non-avian
dinosaurs is their feathers feathers
were long thought to be exclusive to
birds among vertebrate animals but this
was not the case
millions of years ago some non flying
vertebrates had feathers too so we now
know that feathers are not unique to
birds feathers first evolved in
non-avian dinosaurs and it's quite
possible they evolved for something
other than flight possibly insulation
possibly routing their nests but aside
from sharing feathers how do we know
that birds evolved from dinosaurs and
how were these land-based animals able
to take to the skies over the last 200
years paleontologists have begun to find
amazing evidence that helps to answer
these evolutionary mysteries in the form
of incredibly preserved fossils
Pittsburgh's Carnegie Museum of Natural
History houses one of the world's top
collections of dinosaur bones
among them are striking clues of how
birds and subsequently bird flight
evolved from dinosaurs this is a cast of
Archaeopteryx and when this was
discovered well over a century ago it
astounded scientists because the fossil
shows a mixture of features classically
associated with reptiles and classically
associated with birth
archeopteryx was the first of a whole
new group of animals it was a bird
distinguished from a feathered dinosaur
by its ability to fly even though it may
not have been very proficient in the air
there were clear differences in the
anatomical structure of this creature
compared to non flying dinosaurs as the
world's oldest known bird however it
naturally had not completely evolved
away from its ancestors Archaeopteryx
when we look at its skeleton it shows
many features that are retained from its
dinosaur ancestors that are lost in
modern Birds
so for instance if we look at the skull
of Archaeopteryx we see that it retains
tiny teeth all known birds alive today
lack teeth we also see a long bony tail
in Archaeopteryx a dinosaurian feature
we look at the hand of Archaeopteryx we
can see that its fingers are still
tipped with large curved claws and this
is a feature that dinosaurs have as well
in addition Archaeopteryx also seem to
be missing something else crucial
muscles modern birds have a series of
large pectoral muscles that attach to
their sternum and help them generate
enough force to fly
Archaeopteryx didn't appear to have
these muscles so while their bodies
could support some flight it is unlikely
they could stay airborne for very long
periods of time
Archaeopteryx probably could fly but
compared to modern Birds was almost
certainly very clumsy we know this
because its skeleton is much more
primitive than that of modern birds so
how did modern birds evolved to become
more efficient fliers what was the next
evolutionary step after Archaeopteryx
[Music]
in 2004 on a dig in northwestern China
Lamanna and his colleagues came across
another fossilized piece to the puzzle
the more I looked it became clear that
we were looking at a very bizarre group
of birds that were abundant during the
Cretaceous period the final period of
the age of dinosaurs close to a hundred
nearly complete skeletons of a hundred
million year old birds were recovered on
the dig among them a rare specimen tiny
fragments of this long extinct animal
called Ganz's had been found before but
never a skeleton as complete as this one
anthis dates to 40 million years younger
than Archaeopteryx about a hundred and
ten million years ago and already
relatively rapidly in bird evolutionary
history gaseous has acquired many of the
features that we associate with modern
birds it's in many ways an anatomically
modern bird from a hundred and ten
million years ago although Archaeopteryx
was capable of flight Lamanna would soon
discover that Ganz's had anatomical
features that almost certainly made it a
far better flier a lot of the story of
the evolutionary history of birds has to
do with the increased efficiency of
flight so for instance when we look at
Archaeopteryx we see features that are
not present in modern birds such as
teeth and a long bony tail these are two
features that have long been argued to
have been lost in modern birds because
they saved weight loss of teeth a
shorter tail and other distinguishing
features appears to make Kansas an
intermediate animal between the largely
dinosaurian Archaeopteryx on one side
and modern Birds on the other but the de
fossil have the pectoral muscles that
could help it get airborne more easily
than Archaeopteryx
trouble was although the Ganz's fossil
was complete it was also badly flattened
making it nearly impossible to see the
certain anatomical features of this new
species would critical questions to this
mystery go unanswered
fortunately Lamanna is able to turn to a
team of paleo sculptors and artists at
the Carnegie Museum of Natural History
to try and recreate the image of this
ancient bird working like crime-scene
investigators the team is able to
methodically reconstruct the crushed
bones and create a picture of what
Ganz's would have looked like as Lamanna
had hoped Gann disappeared to have a
body capable of supporting large strong
wings the presence of a bony sternum on
Ganz's means that this creature would
have most likely had larger pictoral
muscles compared to the relatively puny
ones seen on Archaeopteryx today all
flying birds have large muscles similar
to those found in Ganz's this provides
them with the strength needed to flap
their wings and get airborne could
Ganz's have been the evolutionary step
to allowing birds to become more
proficient fliers just got what it has
pretty big pecs you know able to flap
his arms with quite a bit of force is
probably this pretty good flier
the large breastbone that strong flight
muscles could attach to is clearly seen
in Kansas as well as fused wrist and
hand bones a short bony tail and fused
ankle and foot bones also traits in most
modern birds all these features
transform these early fliers from a
reptile that could get airborne to a
radical new lineage that would spend the
majority of its time in the air gasps
this was probably an excellent flyer
probably as good a flyer as are many
types of modern birds birds are one of
the most successful groups of
vertebrates but in order to survive in a
new environment major anatomical changes
had to be made what was useful on the
ground would hold them back in the sky
when birds gained the ability to fly
from dinosaurs it came with some costs
they had to lose a few things the most
obvious of which is probably that they
don't have anymore hands all the bones
of the fingers are now incorporated in
the wing and there are feathers attached
to them so they can no longer manipulate
anything with their hands or defend
themselves on the ground regardless of
this cost however the fossil record
clearly shows that the evolutionary
transition from dinosaurs to birds with
a great triumph and over time birds
radiate far and wide
[Music]
these groups that involve the ability to
fly and diversified into hundreds or
thousands of species have gone on to
fill many different niches of the
environment incredible fossils like
Archaeopteryx and Ganz's help us to
understand what anatomical features
define a bird and when they evolved but
what were the environmental factors that
send birds into the air when we're
trying to examine the origin of flight
of birds we need to answer a couple of
questions and perhaps the biggest one is
what were the selective forces thriving
birds into the air
what was happening down on the ground
that turned two footed feathered
dinosaurs into masters of the sky
through the fossil record we know that
birds that were capable of flight
evolved from dinosaurs over a hundred
and forty million years ago but the
biggest mystery of all still remains
what forces would have driven land-based
creatures to take to the skies when
somebody asks what was the behavior of a
fossil of course we're reaching in to an
area speculation cities how do we
explain each of the transitional stages
from the birds dinosaur history to today
ken dial professor of biology at the
University of Montana thinks the answer
of how flight first evolved lies not in
the bones of long dead animals but in
the behavioral patterns of those that
are living what we're trying to do is
we're trying to borrow from the present
to try to interpret the potential
behaviors of the fossil creatures dial
and his colleague Brandon Jackson run an
avian Flight Research Center in the
foothills of Montana
their work focuses on uncovering the
origins of bird flight why do birds need
to fly why do they want to fly daya
believes that birds evolved the power to
fly slowly over time environmental
pressures like escaping predators push
them towards the sky and various
physical adaptations allowed them to get
there if this is true claims dial many
birds may still be hardwired with the
behavior of their land dwelling
ancestors inside in other words if given
the choice between using their wings or
their feet birds will choose to remain
on the ground to test their hypothesis
dial and jacks and put birds in a
position to have to choose between
flying and keeping their feet
earthbound they take birds that are
fully able to fly and place them at the
foot of a ramp with a steep incline
there we go what they observe is that
these birds choose to run keeping both
feet grounded rather than fly to the top
of the ramp changing the steepness of
the ramp does not alter the result
starting with a 30 degree incline then
60 75 and finally 90 each time the bird
chooses to run instead of fly
when we look at the angle which they're
trying to scale we've come to learn
something very very special and that is
if a bird is trying to ascend something
that is less than 60 degrees they can do
so easily just with their hind limbs and
with their wings tucked to their side
but as soon as they start to scale
anything higher than about 60 degrees
you'll automatically see the wings jump
in to the whole process
dile has termed this behavior of wing
assisted inclined running at these
steeper inclines
the birds flapping wings provide
additional power to support the hind
limbs and assist in keeping the bird's
body from falling down the ramp instead
of making a big jump from running on the
ground to flying
running up inclines with the wings
assisting their legs provides small
incremental evolutionary adaptive stages
for the birds to slowly grow larger and
larger wings and more powerful flight
apparatus at a 90 degree angle the wing
beat frequency and force produced
approaches that needed for flight so if
we were to take a bird running on a 90
degree ramp a vertical ramp and then
take the ramp away the bird would not
have to change a thing it wouldn't have
to change its wing stroke angle and
wouldn't have to change its wing beat
frequency and it would be fly could the
desire to keep their feet on solid
ground instead of flying via remnants of
their evolutionary past we think that
they have this ingrained in their
neurocircuitry that if their feet are
touching the ramp they have to run up
it is possible that they stayed
earthbound because for the millions of
years before they could fly their
dinosaur ancestors were land dwellers
Dial and Jackson hope to get a clue as
to how in grains behaviors and birds
they conduct the experiment again this
time using baby chicks that haven't yet
learned to fly the result the same as
with the adult flying pigeons the baby
chicks run up the ramp and as the
incline gets steeper they flap their
little wings harder and faster
Jackson believes that this behavior can
explain the evolutionary steps that the
dinosaur ancestors of birds those
without fully formed wings may have
taken to develop the adaptations needed
for true flight over millions of years
most likely theropod dinosaurs went from
running on level ground to running up
shallow inclines and when they hit 60
degrees they had to start using their
pre wings they're flightless little for
arms now over millions more years they
move from being able to run up 60
degrees to being able to run up 70
degrees and then 80 degrees and then
finally vertical the incremental steps
over many millions of years produce
bigger wings stronger muscles and more
fine-tuning of the wing stroke which
natural selection acts on and bird
flight evolves what were the Selective
forces driving birds to develop a full
wing and the ability to produce
significant aerodynamic forces one of
the strongest Selective pressures out
there is the risk of predation the
ancestors of birds were small bipedal
theropod dinosaurs they only use their
hind limbs for moving to avoid predation
they could try and outrun a predator or
they could run up obstacles to get away
by gaining some kind of elevated refuge
they are safe
over time the chase between predator and
prey grew more intense and to get away
these small theropods had to develop the
ability to run up steeper and steeper
inclines to escape until they had the
power needed for flight once in the air
away from the Predators below birds
could also take advantage of other
benefits such as more diverse and
readily available food sources flight
allows birds to exploit niches that non
flying animals cannot exploit the
ability to soar over a prairie in hunt
for small rodents like hawks and eagles
ooh is only available as a niche to
flying animals Dials experiment may have
finally proven how and why birds first
took to the sky but how did they defy
the laws of gravity and stay up there
once birds had evolved and taken to the
skies the question still remains how do
they seemingly defy the laws of gravity
and stay up there the simple answer
would seem to suggest by flapping their
wings but the evolutionary process that
allowed birds to successfully take to
the skies would require several unique
physical adaptations insects the first
animals to fly are very lightweight and
so don't really require much energy to
stay airborne and unlike birds they
don't stay in the air for prolonged
amounts of time
[Music]
vertebrate fliers like birds are bigger
and need huge amounts of energy to be
able to produce the aerodynamic forces
needed to propel them forward
the primary engine to produce these
forces for birds are their wings in an
airplane you have a engine and a wing
and the engine produces forces to
overcome drag and the wing produces
forces to overcome gravity but in a bird
the wing produces both thrust and lift
evolutionarily birds have perfect
physical features for life in the skies
their wing is naturally curved on the
top and relatively flat underneath lift
is created by faster air flowing over
the top causing it to be pulled up as
well as increased pressure pushing
against the bottom of the wing and when
they flap their wings they generate
enough force to propel themselves
through the sky and not just glide as
far as we know birds produce all of
their aerodynamic forces and the
downstroke so they move their wing from
above their body using the pectoralis
muscle drive the wing down that produces
all of the lift and all the thrust
95% of the power required for this
downstroke comes from a single muscle
the pectoral muscle on average about one
fifth of a bird's body mass is devoted
to this main muscle that powers flight
as this muscle evolved to get larger
over time it was able to create even
more energy and make birds even better
fliers
also crucial to bird flight is
orientation birds have the unique
ability to always tell what is up and
what is down when they are moving
through the air especially when they are
turning airplanes have thousands of
dollars worth of equipment to find the
horizon but birds don't have any of that
instead they have all that in their head
in their brain one thing that they have
is essentially like an internal
gyroscope if you take a bird and rotate
it its head stays essentially level this
is in stark contrast to most mammals
which have a large muscle anchoring
their skull to the neck so the head goes
where the body goes so when Birds turns
they Bank their whole bodies and they
have to keep their head perfectly
straight so that they don't lose track
of where the ground is but it may be
another advancement that has proved the
most crucial in Birds evolving the power
of flight the key to virtually every
land animal success is the ability to
process oxygen in order to be able to
have enough energy for flight birds have
developed a revolutionary use of oxygen
the problem is that they need to take in
huge amounts of energy and oxygen the
secret lies in the birds internal
structure birds like pterosaurs have
hollow bones that connect to sacks
filled with air these pneumatic bones
are really the footprints in the
skeleton of an air sac system air sacs
system is there to provide the oxygen
that flight requires
what is an air sac system and how does
it work
vertebrate paleontologist lay on
Klassen's from the College of the Holy
Cross studies this intricate system in
various species of bird
unlike mammalian lungs which expand and
contract when you breathe in and out
lungs and birds are fixed in size they
never change in volume when fresh
oxygen-rich air is inhaled and used
carbon dioxide rich air is exhaled but
what a bird has to actually move air
around in its respiratory system is a
whole series of what are called air sacs
which are balloon like extensions that
hook up to the various Airways by
juggling air between these various air
sacs birds are capable of getting a
highly efficient air flow through their
lungs by continuously extracting oxygen
from air stored in the sacs both as they
breathe in and also when they breathe
out
at Harvard University's Concord field
station Klassen's and his associates use
an x-ray video technique called sinha
radiography to observe how this unique
air sac system works classes positions
the bird inside the device where the
video captures images of the air sacs at
work you can see right here on this film
that as the rib cage and largest the
majority of these air sacs and
especially the ones toward the tail end
of the animal greatly increase in size
these air sacs allow the animal to
continuously shift air around as and
when they need it and provides them with
a highly efficient breathing apparatus
that is unique to birds you see right
here with Anatomy in action in the
rhythm animal one of the most elegant
and most efficient designs that this
president any living vertebrate and
living backbone air-breathing animals
all living birds today have air sacs and
there's evidence that they were present
in some dinosaurs so they must have
evolved long before birds ever took to
the skies a large dinosaur such as
Tyrannosaurus you have evidence for the
presence of air sacs because you have
openings in the bones where parts of
these air sacs has invaded the bones
anatomy that had already evolved in
ground running dinosaurs like air sacks
and feathers was fine-tuned by natural
selection to produce great fliers this
unique Anatomy would pave the way for
10,000 species of birds to populate
every continent on Earth but 55 million
years ago one of the good mammals with
none of the features that birds have is
about to conquer the skies in a whole
new way when the Sun sets the majority
of birds retreat from the sky and give
way to an entirely different animal the
fourth and final lineage to evolve the
power of flight are the Masters of the
night bats bats are the only mammals who
have not remained ground-dwelling
creatures
more than just freaks of evolution bats
are one of its greatest success stories
with over a thousand species worldwide
they make up 20% of all mammals bats
evolved the power of flight in an
entirely unique way without any of the
features that make birds so successful
feathers hollow bones or even air sacs
birds and bats are completely separate
in their evolutions they each represent
the arrival at flight by a different
evolutionary pathway but what forces
drove them to be the lone mammals in the
air around fifty five million years ago
and how did they manage to do something
very few birds ever could take to the
sky at night we're pretty confident that
bats evolved from some kind of ancestor
that with a glider that used flaps of
skin to move through the air without
flapping six groups of gliding mammals
still exists from marsupials to the
flying lemur and the flying squirrel but
only bats evolved powered flight exactly
why remains a mystery but Sharon Swartz
who studies bats at Brown University
thinks it had something to do with their
ancient gliding lifestyle one major
function of biting is that it provides
an excellent way to escape predators at
a moment's notice
physically bats acquire the power of
flight in a very distinct way from birds
when they evolved they retain the five
independent digits of a mammalian hand
which were covered in skin to make a
wing
schwartz and her colleagues studied the
abilities of the bat in the sky by
observing them flying in a wind tunnel
that comes from animals ancestors have
had five separate fingers and those five
separate fingers were used to control
and manipulate lots of aspects of the
environment around them when bird wings
evolved from dinosaur four limbs they
lost any trace of grasping digits that
used to be there but it is these
mammalian fingers that bats have
retained that make bat flight so novel
and so different from how birds fly bird
wings are fixed and always in alignment
mirror images of one another bats on the
other hand can use their fingers in
nearly twenty joints to manipulate each
wing separately quickly altering the
path it takes more like the oars of a
boat than the wings of a plane this
unique ability to control their wings
has made bats the top guns of the sky
they can steer and brake instantaneously
and are able to change their direction
up to ten times faster than a bird so
when we look in the night sky and see
bats darting in a riot of angles and
speeds what we are seeing is not the
loss of control but in fact the
mastering of it
but it is when we see bat taking to the
sky that represents something else
unique about their power of flight they
are one of the few vertebrate fliers
that have mastered the night sky dr. Jim
Simmons of Brown University says a
simple environmental factor may have
driven them their predation at night
there are huge numbers of insects that
have evolved to be active in parts to
avoid being attacked or eaten by birds
and the bats are out now exploiting this
huge resource of the insect to fly at
night without any serious competition
while food may have driven some bat
species into the night sky how do they
do it don't forget they're flying in
total darkness so for the most part
visual information isn't even available
to me what traits have they developed to
allow them to navigate in the dark for
some bat species the answer is a
built-in sonar device echolocation
echolocation is the process where
animals call out to the environment and
listen to the echoes of those calls that
return from various objects in front of
it in bats these calls are on a
frequency too high to be heard by the
human ear this radar-like system gives
bat an advantage when navigating at
night aside from bats only whales and
dolphins have evolved this system and
bats are the only flying animal to use
this technique to navigate their way
through the skies
in his lab Simmons shows just how
precisely a bat can fly in total
darkness change serve as obstacles and
the bats chore is to fly in here and
maneuver around the chains using its
sonar just the way it has to maneuver
around the vegetation but upon now the
chains are black and the room is black
when the lattice flying the lights are
off as completely dark in here
so the bat is forced to use its sonar
instead of any residual vision that it
might have here we go no matter how many
times Simmons moves the chains to create
new obstacles the result is the same the
bats safely navigate from one side of
the room to the other in total darkness
relying only on their echolocation these
nocturnal fliers have evolved to use
their ears almost in the same way as an
eagle uses its eyes to detect prey in
the air this highly evolved system is
what allows bats to live and fly very
successfully in total darkness one of
the things about the evolution of
banished is that you can't treat their
flight as separate from their
echolocation and their hearings the two
go together the two works so well
together that over a thousand species of
bats have radiated out across the world
along with over 10,000 species of birds
and over a million species of insects
our skies are bursting with flight both
night and day the ability to fly is
arguably the evolutionary outcome that
has most grabbed the human imagination
and by studying the amazing features of
the four different flying animals
pterosaurs
insects birds and bats humankind has
been able to do what they once thought
was impossible and take to the skies but
our man-made machines pale in comparison
to the true marvels of natural flight
due to spectacular evolutionary
advancements over millions of years land
and water are no longer the only places
teeming with life
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