Do you regularly wonder how to hold your body weight with just your arms, while making them flutter frantically to stay in the air? no ? Perhaps we underestimate the muscular strength and anatomical dexterity necessary for the flickering flight of birds. The birth of their ward was very mysterious until recently, but this origin has been clarified thanks to exceptional excavations!
The great anatomical innovation that distinguishes birds is undoubtedly their wing, which is a modified and highly specialized forelimbs. Yes, if we are interested in the wing bones of birds, or the bones of bats, we realize that they are actually highly modified arms! They are said to be homogeneous structures because they have a common origin. But how and when did such a modification emerge? This is what the study authors report in the journal Animal Science Letters.
Understand the structure of the wing
Modern birds are mostly able to move through the air thanks to what is called flapping flight, unlike gliding which does not require the same figure, even if any animal capable of the first can do the second. , but not the other way around. Because you need solid, specialized muscles to lift your wings. In birds, one of the structures without which it would be impossible for them to make this active flight is the propatagium. The word patagium simply refers to the membrane of skin that gives shape to the wings of bats, or pterosaurs, and serves to provide a lifting surface for the wing. Birds have more feathers to fulfill this role, but they also have less patagium, especially between their shoulder blades and wrists. The propatagium contains a muscle, called the proptagialis, unique among vertebrates, that helps birds flap their wings.
It’s not impressive, so thin and tense that we often take it as a chord, so why bother with it? In current birds that no longer fly, such as ostriches or penguins, we see a loss or reduction in reproduction. This is used to extend the wing. When the elbow opens, this muscle automatically causes the simultaneous opening of its wrist, and facilitates control of wing flapping. To better understand the origin of bird flight, the study authors attempted to pinpoint the moment in the evolutionary history of this group when the Propategiales appeared by looking at fossils.
Interpretation of bird fossils
This was no small feat, as soft tissues are rarely preserved during fossilization. To circumvent this problem, the researchers had a clever idea, they were interested in the fossils for the skeletons in relation to where the bones were still articulated as they were during the animal’s life, and they noticed their elbows. This is because the propatagialis, which attaches to the wrist, prevents birds from fully extending the elbow joint. The scientists were able to demonstrate that the angle of elbow opening was thus a good predictor of the presence or absence of propatagium. While studying the arthropod fossils of very ancient birds and their close cousins, they made a startling discovery.
A small reminder: birds are classified among dinosaurs, they are even theropod dinosaurs, such as tyrannosaurs, therizinosaurs or the famous dinosaurs Velociraptor ! This is classified, like modern birds, within a smaller group of Maniraptorians, and the study shows that the latter may have had a propatagium. So it was their non-avian cousins much older than the birds who saw the emergence of this structure, and thus the wings themselves. It is now a matter of what was the use of this structure by the presumably basal Maniraptorians who did not fly. The authors do not believe that the initial cause was adaptation to flight, as their front paw was much better able to fly!