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.
Bruce W. Fouke, Ph.D.Director of the Roy J. Carver Biotechnology Center
