PREVIEW

A group of Korean scientists have built a robotic feathered dinosaur in a bid to prove the prehistoric lizards flushed out prey like modern birds.
Experts have long accepted that feathered dinosaurs evolved into birds. Some of these beasts had feathers on the tails and small wing-like feathers on their forelimbs (arms).
These small wing-like structures called ‘proto-wings’ are composed of special feathers known as pennaceous feathers — the stiff feathers found in the wings and tails of birds.
However, it has been known that these proto-wings were too small for powered flight. So what they were for has remained a mystery.
A new scientific collaboration involving a team of field-biologists and integrative ecologists (Piotr G. Jablonski, Sang-im Lee, Jinseok Park, Sang Yun Bang, and Jungmoon Ha), paleontologists (Yuong-Nam Lee and Minyoung Son), and roboticists (Hyungpil Moon and Jeongyeol Park), has proposed a new idea: the ‘flush-pursue hypothesis’.
Some birds employ a 'flush-pursue' foraging strategy, using wings and/or tail displays to visually flush out hiding prey and pursue it. The hypothesis suggests that small dinosaurs with proto-wings use a similar strategy.
The hypothesis is rooted in years of detailed field-ornithological studies on several species of insectivorous birds conducted by a co-author of the current study, Piotr Jablonski and collaborators. Studies on these birds have revealed that displaying contrasting plumage (often with black-and-white patches) on the wings and tails that makes their prey try to escape.
In order to test the thesis the team chose one dinosaur, Caudipteryx, and built a robot in its likeness that they could operate to test whether the behaviour scared the kind of insects they might have preyed on.
The robotics team led by Hyungpil Moon, an expert in robotics, constructed the robot named Robopteryx and programmed it with wing and tail displays used by existing flush-pursuing birds to trigger escapes in their prey visually.
Equipped with nine motors, ‘Robopteryx’ was programmed to imitate the movements of forelimbs and tail of ground-foraging flush-pursuing birds, such as the greater roadrunner, within the anatomical constraints determined from paleontological literature by Minyoung Son, an expert in the anatomy of Cretaceous dinosaurs.
Jinseok Park (the first author of the paper and a field-ornithologist focusing on avian diet and foraging), with a team of field-biologists, conducted tests with ‘Robopteryx’ to observe behavioral responses of wild grasshoppers, which belong to the ancient order Orthoptera likely to co-occur with pennaraptoran dinosaurs.
The results revealed that grasshoppers escaped more frequently when proto-wings were present on the forelimbs, compared to displays without proto-wings. Additionally, grasshoppers fled more often when the proto-wings had white patches, compared to when they were plain black. Moreover, grasshoppers escaped more frequently when tail feathers were present, particularly when the area of tail feathers was large.
Since the reactions of simple neural circuits involved in escapes in insect prey are crucial for understanding the evolution of flush-pursuing strategy in birds, the researchers decided to compare the responses of neurons of grasshoppers to the hypothetical displays by the dinosaurs.
“I created computer animations imitating the hypothetical displays by Caudipteryx and presented them to grasshoppers in the laboratory,” explains Jinseok Park. "I used easily available inexpensive equipment to record responses of neurons,” Jinseok adds.
The researchers found that the reactions of neurons, particularly peak firing rates, were higher in response to the animations with proto-wings than those without.
Based on the results, the researchers argue that dinosaurs’ prey would have been more likely to flee when proto‑wings made of feathers were present, especially near the end of the forelimbs and with contrasting patterns, and when the tail feathers, especially of a large area, were used during hypothetical flush‑displays.
Sang-im Lee, the integrative ecologist member of the research team adds: “We propose that using plumage to flush prey could increase the frequency of chases after escaping prey, thus amplifying the importance of proto-wings and tails in maneuvering for successful pursuit. This could lead to the development of larger and stiffer feathers as these would enable more successful pursuits and more pronounced visual flush-displays.”