Birds today, especially those which can fly, have a specific wing structure known as propatagium. As per Science Daily, birds will not be able to fly without this structure.
However, its evolutionary origin has been unknown and remained a mystery to science. Now, a study reveals that it developed in non-avian dinosaurs based on a statistical analysis of arm joints preserved in fossils. Scientists believe that this could be the missing link in the knowledge of the origin of bird flight.
Missing Link on the Origin of Bird Flight Traced Back to Non-avian Dinosaurs
What Is Propatagium?
Dinosaur fossils with bent elbows and wrists may indicate the presence of an unpreserved tendon that supports all current bird flight, Science Alert reported. Researchers at the University of Tokyo think that the stance could reveal information about the evolutionary route of bird flight, which has remained one of paleontology's greatest mysteries.
Approximately 200 million years ago, pterosaurs became the first animals to accomplish genuine lift-off. But, these gigantic prehistoric reptiles were not dinosaurs, allowing the direct ancestors of birds to find out how to fly on their own.
Avian dinosaurs would not develop from two-footed feathered theropods until at least 80 million years after pterosaurs had attained powered flight. Birds employ a very similar mechanism to pterosaurs to remain aloft, a system that, like feathers, appears to have developed long before flying began.
A propatagium is a membrane found in all living vertebrates that flap their wings, including birds and bats. A comparable feature may be seen over the upper limbs of several gliding animals.
To visualize a propatagium, extend your arm out to the side with a bent elbow and wrist. Consider a tendon running from your shoulder to your hand, forming a bridge or the wing's leading edge. During a flapping action, this 'bridge' permits flying birds to flex and extend their wrist and elbow in tandem, providing lift to a bird's flight, and allowing the animal to manipulate two joints at the same time.
The propatagium's purpose in pterosaurs is less apparent, although it appears to have regulated flight take-off and landing by regulating the flow of air over the wing's top surface. Several experts believe that without the tendon, birds, bats, and dinosaurs would never have gotten off the ground.
Evolution of Bird Flight
Tatsuya Hirasawa, a paleontologist from the University of Tokyo, explained in a statement via Phys.org that propatagium is not present in other vertebrates and has disappeared its function in flightless birds. To understand the evolutionary origin of bird flight, Hirasawa noted that understanding how the propatagium arose should be the first step.
Yet, because the propatagium is made up of soft tissues that do not fossilize well, if at all, direct evidence may be impossible to locate. So, researchers had to devise an indirect method of determining the existence or absence of a propatagium in a specimen.
Yurika Uno, a graduate student in Hirasawa's group, said they collected data on the angles of joints and arms or wings of a dinosaur and bird.
They found that the propatagium most likely arose in the maniraptoran theropods, which included the legendary Velociraptor. The discovery of the propatagium in surviving soft tissue fossils of the feathered oviraptorosaurian Caudipteryx and the winged dromaeosaurian Microraptor supported this finding since they predated the emergence of flight in that lineage.
The findings establish when the propatagium first appeared, which leads researchers to the next question of how it came to be and why these specific theropod species required such a structure to better adapt to their habitat. The findings of their study, titled "Origin of the Propatagium in Non-avian Dinosaurs," is published in Zoological Letters.
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