How did life emerge on Earth? How have life and Earth co-evolved through geological time? Is life elsewhere in the universe? Take a look through the 4-billion-year history of life on Earth through the lens of the modern Tree of Life! This course will evaluate the entire history of life on Earth within the context of our cutting-edge understanding of the Tree of Life. This includes the pioneering work of Professor Carl Woese on the University of Illinois Urbana-Champaign campus which revolutionized our understanding with a new "Tree of Life." Other themes include: -Reconnaissance of ancient primordial life before the first cell evolved -The entire ~4-billion-year development of single- and multi-celled life through the lens of the Tree of Life -The influence of Earth system processes (meteor impacts, volcanoes, ice sheets) on shaping and structuring the Tree of Life This synthesis emphasizes the universality of the emergence of life as a prelude for the search for extraterrestrial life.
6.6. Wild Wings: Fit to Fly
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Из курса от партнера University of Illinois at Urbana-Champaign
Emergence of Life
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Week 6 - Mesozoic Reign of the Dinosaurs and the Development of Flight
This week, you'll learn more about the Permian-Triassic extinction event, which caused more than 80% of life to go extinct. This opened vast swaths of ecological opportunity for radiation and diversification of life during the Mesozoic. You'll learn about symbiosis, which was widely utilized during this period, as well as the fascinating lineage of diapsid reptiles that rose to replace the synapsid predators of the late Paleozoic. We'll also discuss the rise of the dinosaurs, as well as the catastrophic meteor impact that drove the dinosaurs to extinction.
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Bruce W. Fouke, Ph.D.Director of the Roy J. Carver Biotechnology Center
Department of Geology, Department of Microbiology, and Institute for Genomic Biology
[MUSIC]
Today, we're talking about the development of flight.
So it's pretty exciting to consider this development, because it's happened three
different times that we're aware of over evolutionary time.
So to start to kind of dial you in here, we're talking about birds,
pterosaurs, which you may know as pterodactyls and bats.
The development of flight is beneficial,
because those organisms can cover large territories.
They can cover a lot of ground and that's useful for searching for food,
fleeing from predators or perhaps, protecting their offspring.
So what we want to consider here is that,
again flight has developed three separate times over every evolutionary time.
And that development or those characters,
the wings that facilitate flight those are called Analogous Characters.
And so, what that means is that we have these three different groups of organisms
that can fly.
Again, birds, bats and pterosaurs, but
they don't stem from the same evolutionary branch I suppose.
So there are actually three separate groups that our deeply rooted relatives
in an evolutionary time, but they're not closely related there.
So if we can continue on in our discussion here, we'll focus in on the first
class that has developed flight and that's class Reptilia, which is rather unusual.
Again, this is in the class Reptilia and the order pterosauria.
So we can kind of break down that word, so
that you can remember it a little bit better.
Ptero or Pter, the beginning of that word refers to wings or one with wings and
saur is lizard.
So we have the pterosauria, the winged lizard group here.
So these developed in the late Triassic and
they went extinct in the end of the cretaceous.
These were the first flying vertebrates.
How we can distinguish which group is which?
So which class, we're looking at if we're examining a fossil is based almost
solely on the wing morphology.
And so if we can dial in again to the class Reptilia to be specific here,
we have a pterosauria here.
And I'll kind of trace the arm, so
that you can take a look here at the wind were follow you.
So, we start with a humerus.
We have the radius and ulna, just like in humans and
then we get to the kind of the carpel area and the hand region and
what I want to draw your attention to is this elongated fourth finger.
And so why I'm calling it the fourth finger is because we can kind of count
the other fingers honestly, here on this cast.
So, here's the first.
Here's the second.
Here's the third and here's our elongated fourth finger that provides
the axial support for the wing of the pterodactyl.
And so, something that we want to remember about the pterodactyl or
the pterosaurs is that specimens of the pterosaurs are found all over the world.
So, we know that this development of flight was allowing them to just
scatter all over the Earth and occupy several ecological niches.
The second class that has developed flight is the class Aves and these are the birds.
So, you'll be most familiar probably with this class of fliers here.
So, birds developed in the upper Jurassic.
And obviously, they're still around today.
So, we'd call that the upper Jurassic to the recent.
These are the most successful fliers and they're both extremely abundant, and
diverse.
One of the key features of this class is the evolution of feathers.
So feathers are thought first, be developed for protection from weather.
Secondly, their vital to flight and
something we want to consider about feathers is their origin.
So, some scientists hypothesize that they developed from scales.
So one of the ideas that have helped the development of that hypothesis
is that reptile scales are made of keratin,
kind of a tough fibrous material and feathers are also made of keratin.
So, it's possible that reptile scales eventually led to the development of
feathers.
Kind of interesting there and unusual.
Another distinguishing feature of this class Aves or the birds is the presence of
an enlarged sternum or your breast plate you might think of,
this big bony covering in the front that has a prominent keel.
And what the keel is, is kind of projecting big bony plate that provides
the point of origin for big pectoral muscles that'll power the wings
that basically allow that flight to happen.
And so, that's a distinguishing feature.
If you find a specimen that has kind of an enlarged breast plate there and
an enlarged sternum with a big prominent bony plate,
that big muscles can attach to, that would clue you in that that's the class Aves.
Additionally, the class Aves, they have sturdy hips, which is thought to be for
landing actually.
So if you can think of trying to defy gravity and then you're coming in hot,
if you will from flight, you're going to need a sturdy support structure on that
pelvic girdle to support the organism, basically, as they're landing there.
Lastly, we want to dial in to the way morphology of the class Aves,
because we're using that to distinguish between the other two classes that have
developed flight.
So the wing morphology of the birds is, it's called fused fingers.
So basically, the end of the upper arm has been fused together into kind of
a sturdy structure basically that would help cut through the air and
sort of provide a more aerodynamic structure for the wing.
So if we want to look at the morphologies and the characters a little bit
more specifically of class Aves, we'll take a look at our sparrow specimen, here.
So, what we see here is the fused finger wing morphology.
So, I can kind of point out where we're looking here.
You'll see clearly that the digits of this organism have been fused together into
one little sturdy structure at the end of the wing.
I show you here.
So we have our humerus here, kind of folded up that under and
then here's kind of elbow region.
We're going up into the radius and ulnar or the forearm, if you will of this bird.
And then the fused fingers right at the end of his arm here,
providing the support structure for the wing.
Lastly, just to point out here on an actual specimen, we can see the prominent
sternum or the sternum in the prominent keel here on this sparrow.
So the sternum is just kind of this center support structure of bone right in
the center of the bird and then it extends upward into this big bony plate,
that's called the keel.
Providing that point of origin for
those big pectoral muscles that will power the wings.
When considering the class Aves, we want to think about the origin of that group
and how flight even began developing from reptiles.
And so here we have a great cast of an Archaeopteryx, which is thought to be one
of the predecessors or one of those kind organisms that are bridging the gap
between the reptiles and your flying birds here.
And this cast shows the reptile form and
the presence of the tail here, but other specimens have been
found with an impression of feathers actually surrounding this organism.
So, there is definitely some evidence that this is an organism that's
bridging the gap between reptiles and the flying birds.
The third class that has developed flight is the class mammalia and the order
Chiroptera is actually the specific group of organisms that's developed flight.
And so these are your bats, basically.
And Chiroptera, if we could break down that word a little bit, chir or
chire means handed and then ter, again is wings.
So, we have a hand wing here and
you'll see why in just a minute when we look at our specimen.
So what we want to consider here is that bats develop in the Eocene,
which is very recent.
And then obviously, they're still around today.
So, the Eocene to the recent is the class mammalia here.
So the wing morphology, again, that we're using to distinguish these
different classes is that bats exhibit basically elongated fingers.
So all four fingers are greatly elongated and the provide kind of
a skeletal structure to the wing there, to the soft parts of the wing.
And so those four fingers are different from the birds, because they're not fused
together providing kind of a sturdy stiff support structure, but they're actually,
well, I might say rather flimsy, a little scary, but they do they fly very well with
these elongated four fingers providing the structure for their wings.
So if we can look at our specimen here, he is a little bit difficult to
to distinguish which are the fingers here, but I'll try to point them out here.
So if you can imagine,
his wings are kind of folded up almost underneath his body here.
So, what we see here is we have the humerus coming off kind of
the axial part of the body.
Our humerus here.
Our radius and ulna coming up, so here's his elbow right here.
And then the four fingers are kind of folded up underneath, so
I'm actually going to draw your attention down to the bottom here where we see four
actual projections here.
So if you can imagine his wings are folded up here, but
we can still see the evidence of the four elongated fingers.
So through evolutionary time,
we've been able to observe three different classes that have developed flight.
And if you think about them kind of generally,
you might notice that they all have wings and that would be the analogous
character that we have identified that provides the same function for
the organism, which is obviously, to fly around.
But if we look a little bit more closely and
dial in onto the actual wing morphology, we can separate these different
flying organisms into their different taxonomical groups.
So just to kind of reiterate here, we have the pterosaurs with their elongated
fourth finger that's providing support for the wing.
With the birds of the class Aves,
we have fused fingers that have a very sturdy structure for the wing.
And then with our class mammalia order Chiroptera here,
we have four elongated fingers that are providing support for the wing.
So what's really interesting about the development of flight is that we have this
one function, which is that the organism is defying gravity and lifting off of
the ground and flying actually, but we have that accomplished through three
different wing morphologies that are very distinct as we've covered in detail.
And so, that's something that has developed three separate times over
geologic history.
That is really amazing to me.
[MUSIC]
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