[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]
