It is evolutions' most inspiring achievement
the power of flight
From insects to birds to bats
tens of thousands of species fill our skies
But hundreds of millions of years ago
flight did not exist
This is something 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 of more than two hundred miles per hour
this bird swoops down from more than
half a mile in the sky to attack
with lethal precision
The paragraph's tremendous speed and success at hunting
can be attributed to one simple trait
the power of flight
While humans of 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 beatles 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 of millions of years nothing could fly
and so if a small invertebrate was moving around
in the forest and wanted to find food
had to crawl all the way up to
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 fly organisms appeared
and once flight became part of the game
it changes everything
The fosil record shows that insect flight evolved suddenly
around three hundred and fifty millions 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 niches 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 mere forty five pounds
If you watch birds in 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 Quetzalcoatlus
This is Quetzalcoatlus
the largest flying animals of all time
with wingspan of about thirty-five 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 it physically possible?
Weighing hundreds of pounds it seems unlikely even at
even its massive wings could have generate
enough force to drive it into the air
Pterosauria live 220 million years ago
and were the first vertebrates to evolve powered flight
Their name comes from the Greek pterosaur
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
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 flight of pterosaurs
The part that basically connects the wing itself to the body
Toward most was the flight most attached
When I talked to the curators of museum about the pterosaur collection
It was in fact the last thing they showed me
It was almost an afterthought
They have 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
Habib 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 Habib noted was
something paleontologists have long known about the pterosaurs bones
They were hollow
Hollowness is supposed to be very very large
and the diameters can be very wide which makes them very strong
since they could put a lot of muscle power on them
and the bone will hold up
This bone however was not completely hollow
Habib 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 Habib was able to figure out
what this bone was used for
It was used to help launch pterosaurs
like the 440 pound Quetzalcoatlus off the ground
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 for birds actually not the wings
that most get the bird off the ground
Actually it's the legs
Legs give the initial leap
starts 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 flyers got airbone
but the question remains
Why is there nothing this big flying today?
The answer may be the size of 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
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
not only the ground but also far above in the sky
Two 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 exmple
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 dapted flight
is a 230 million year old detective story
but if you know where to look
there are telltale clues
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 Trex
If we were to look at the foot of a Trex
and put a Trex foot next to the foot of this emu
you see 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 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 tp
take to the skies over the last 200 million 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 birds
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 musles
So while their bodies can 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
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 clearer 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 of 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 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 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
well as fused wrist and hand bones a short bony tail
and fused ankle and foot bones are 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
Ganze 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
was 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 bird flight
we need to answer a couple of questions
and perhaps the biggest one is
what were the selective forces
thrusting 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
area of speculation
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?
Dial 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 have 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 "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
and 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
as to how ingrains behaviors in 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 fore 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
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
or 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
Dial's 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
in birds evolving the power
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
aN 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 in 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 adiography
r 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 larges
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 living animmal
One of the most elegant and most efficient designs
that this is present in any living vertebrate
any 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 sac 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 gives 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 gliding 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
Bats come from animals' ancestors
that 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 nights
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
Chains 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 bats 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
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 bats
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
Tthe 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