Birds relied on four wings instead of two

The blue jay, Hopkins’s school mascot, is named after and commonly known for the impressive blue color of its feathers. However, what may be more impressive than having two beautiful wings is having four of them.

According to a new study by Chinese scientists at the Shandong Tianyu Museum of Nature, some primitive bird species flew with four wings instead of two. The research team, led by paleontologist Xiaoting Zheng, discovered eleven primitive bird fossil specimens that indicated large feathers on their hind limbs in addition to the pair of wings that modern birds still possess.

The fossil specimens were found in Liaoning Province in northeastern China, and include several species, including Confuciusornis, Sapeornis, and Yanornis. The specimens lived around 130 million years ago during the early Cretaceous period.

Previous studies showed that feathered hind limbs were discovered in several dinosaur species, including the Microraptor, the smallest known non-avian dinosaur. Scientists have accepted that the large hind leg feathers of these dinosaurs were used in flight.

But the new study published in Science provides evidence that primitive birds also used their leg feathers in flight. The research team indicated that the flat surface formed by the birds’ large perpendicular leg feathers provided lift, created drag, and enhanced maneuverability, making them capable of flying adeptly.

However, the research team suggested that the way many of the specimens were preserved makes it difficult to determine the precise location and orientation of the leg feathers on the body. All of the specimens were preserved in two-dimensions, as if their bodies had been flattened. Thus, each of the eleven skeletons was preserved with the legs either splayed outward or folded under the body. These characteristics make it difficult to determine whether the feathers extended from the front, back, or sides of the legs.

Our lack of knowledge on these preserved specimen makes it difficult to determine the exact function of the feathers. In order to aid flight, the leg feathers should extend perpendicularly to the leg, but such an orientation is difficult to confirm because of how the specimen were preserved.

Nevertheless, the scientists’ discovery carries implications on expanding our knowledge about avian evolution.

The leg feathers of modern birds are almost always less developed than the arm feathers. In modern birds with leg feathers, such as certain species of chickens, the leg feathers are usually small and fluffy and play a role in insulation and protection rather than flight.

The scientists believe that this is because large leg feathers are not suitable for terrestrial locomotion. Researchers from Linyi University in Shandong suggest that large leg feathers in animals hinder fast running and other terrestrial locomotive capabilities. Loss of large leg feathers allowed birds to run on more streamlined legs that reduced drag and air resistance.

As these primitive birds relied more and more on their legs for walking and running, the large leg feathers gradually disappeared and were replaced by scales or small, fluffy feathers. The arms became specialized for flight and the legs for terrestrial movement, demonstrating the differentiation of the forelimb and hindlimb functions.

However, some scientists are still not convinced of the validity of some conclusions that are being made.

Some researchers suggest that there is no evidence that the leg feathers would have increased lift. In order to increase lift, the feathers would have to be arranged so that they formed a flat surface when they were spread out for flight. No one has shown that this was the case.

Despite the uncertainty of the study’s results, some scientists commend the study because it shows how leg feathers changed over time among primitive birds.

Zheng, Xu and the other scientists intend to examine the thousands of other fossils in the museum’s collection to investigate the functions of the primitive birds’ leg feathers and to determine whether they would have been useful in flight. Had Hopkins existed 130 million years ago, our beloved Blue Jay mascot might have been strutting around Homewood Field with four wings instead of two.