Robot dinosaur tests surprising theory about the evolution of feathers

Feathers may have evolved on dinosaurs to frighten and flush out prey before they were used for flight, say researchers who built a winged robot and used it to scare grasshoppers.

Pennaceous feathers, which are the stiff, non-downy feathers that have a central quill, are seen in fossils of some dinosaurs such as Caudipteryx, which lived about 124 million years ago. These dinosaurs had wings but they were not strong enough for flight, so it’s unclear how they were used.

Jinseok Park from Seoul National University, South Korea, and his colleagues hypothesised that they were used to startle prey into fleeing from hiding places, so they could be caught more easily. This “flush-pursuit” hunting strategy is used by modern birds including the greater roadrunner (Geococcyx californianus) and the northern mockingbird (Mimus polyglottos).

To test this idea, Park and his colleagues built a life-size robotic model of Caudipteryx, nicknamed Robopteryx. The robot approached grasshoppers, which were a likely prey of Caudipteryx, before flapping its wings. Without feathers, just under half of tested grasshoppers fled, but when the researchers attached feathers to the wings, this increased to over 90 per cent.

The team also recorded the neural responses of grasshoppers while they were shown an animation of Caudipteryx. They saw stronger activity in neurons involved in escaping reactions when the feathers were present in the animation than without.

Park says the study demonstrates that flush-pursuit hunting was a potentially crucial factor in the evolution of pennaceous feathers on the arms and tails of dinosaurs.

“This could, in turn, lead to the evolution of larger and stiffer feathers, contributing to more successful pursuits and prominent visual flush-displays,” he says.

Predators with pennaceous feathers would have been able to flush out prey from further away, enabling them to see the trajectory of escaping prey, says Park. That would allow them to catch prey in the air relatively easily, he says. Even if the prey landed in vegetation, the predator could see where it landed and follow them.

“We believe that pennaceous feathers evolved first for flush pursuing and were used later for flight,” Park says.

But Steven Salisbury from the University of Queensland, Australia, says this explanation is probably too simple. “It seems to me to be very unlikely that a structure as complex as a pennaceous feather would evolve for such a specific behavioural role,” says Salisbury. “I am sure there are lots of ways to scare grasshoppers other than to flap some feathers at it.”

There is probably no single reason why feathers evolved, he says. “You can have feathers to scare grasshoppers and you can have them to insulate and incubate eggs; they’re good for display; the stabilisation of body position when running, and of course for gliding and powered flight. Feathers help for all sorts of things.”