What started the evolution of the complex feathers that later propelled birds into the air? A research team is now presenting a new hypothesis on this question: Small dinosaurs could have initially used their feathers on their forearms and tails to scare insects out of their hiding places. Even today, some bird species still use this strategy, the scientists show. They also support their hypothesis through experiments with a dinosaur robot that was particularly successful in scaring up locusts using simulated spring structures.
They are large and resilient and yet light and flexible: the complex feathers of bird wings are among the most important “inventions” in the history of evolution. It is now clear that the history of the development of feathers began with the dinosaurs. It is assumed that in the Jurassic period, representatives of the Pennaraptora group developed more complex shapes from down-like structures that correspond to the flight feathers of today's birds. But what were the complex feathers used for at the beginning of this evolution? The earliest known feather shapes were identified in fossils of small bipedal dinosaurs, which they wore on their arms and tails. However, the body structure of these animals shows that they were not yet able to rise into the air.
What were the feathers used for before flying?
Various possibilities have already been considered as to what purpose the early complex springs might have served. Among other things, it was assumed that they enabled the small dinosaurs to perform more nimble maneuvers when running. But they could also have initially represented a show element in the courtship behavior. It has also been suggested that the long and broad feathers on the protowings were used like a kind of net to prevent prey from escaping. But apparently the previous hypotheses offer space for another one. The research team led by Jinseok Park from Seoul National University in South Korea is now presenting the so-called “scare-chase hypothesis”.
It says that small dinosaurs used their proto-wings to hunt using a strategy similar to that which some insectivorous bird species still use today: When they are constantly searching for grasshoppers etc. on the ground, they repeatedly fold their wings or fold theirs as well Tail feathers jerk up. This causes prey animals to have an intense escape reflex that drives them out of their hiding places. However, this fright reaction usually does not allow them to escape: the birds often manage to snatch the frightened insects. This behavior can greatly increase the efficiency of foraging, according to observations by some of the study authors. It is also interesting that bird species from different groups have developed this “trick”. This may have been the case millions of years ago and then became the basis for the further development of complex feathers, according to the explanation.
A dinosaur robot scares up locusts
To further support the hypothesis, Park's team decided to take an experimental approach: They built the robot “Robopteryx,” which is modeled on the Pennaraptora dinosaur Caudipteryx. It was a robber about the size of a turkey that had feathers on its arms and tail and lived around 124 million years ago. The researchers gave Robopteryx the shape, size and estimated mobility of the model. It was then programmed to imitate the startle behavior, with the full sequence consisting of spreading its proto-wings and raising its tail. The researchers were also able to vary the simulated spring surface. As experimental prey, they chose a species of grasshopper that was known to have had ancestors in the era of the Caudipteryx dinosaurs.
As the team reports, their “scare experiments” showed that when simulated spring structures were attached to the arms, scaring was almost twice as likely to be successful as without the structures. The effect was particularly pronounced when the simulated tail feathers were also presented. In addition, the locusts fled significantly more often when the proto-wings had patterns than when they were simply black. This is a characteristic that some bird species have that use the Scheuch concept. In addition, evidence of color contrasts in plumage was also found in early fossils of Pennaraptora dinosaurs, the scientists explain.
They see their experimental results as confirmation that their hypothesis represents a plausible explanation for the original purpose of complex springs. Finally, the authors emphasize that they do not want to rule out other possible explanations. It is possible that various advantages for larger and stiffer spring structures arose early on. “Several factors may have contributed to the formation of the proto-wings,” say the scientists.
Source: Seoul National University, specialist article: Scientific Reports, doi:
10.1038/s41598-023-50225-x