The problem with being an expert on dinosaur behavior is that little can be inferred from the fossilized bones of animals that died millions of years ago.
For researchers in South Korea, the absence of any living things to observe was simply another challenge to overcome. Enter Robopteryx, a robot that resembles—if one squints and ignores the wheels—the prehistoric, peacock-sized, fan-tailed omnivore, Caudipteryx.
The scientists built the machine to test their ideas about the origin of birds’ wings and tails. Before the first feathered flight, some dinosaurs developed feathered forearms and tails, but these were too weak to get the animals airborne. What drove their evolution is still up for debate.
Dinosaur experts have suggested all sorts of advantages to tiny “proto-wings.” They may have worked as insect nets, preventing prey from escaping, allowing long hopping and gliding, and helping to warm the animal and its newborn offspring.
An alternative hypothesis is that dinosaurs used their feathered appendages in menacing displays to flush insects and other prey from their hiding places. This “flush and follow” strategy, proposed by the South Korean team, is used to great effect in the northern mockingbird and greater roadrunner today.
To test their suspicion, the scientists put Robopteryx in front of unsuspecting grasshoppers and had it perform various wing and tail movements. It was designed to mimic displays that Caudipteryx may have performed around 124 million years ago in the early Cretaceous.
“We always placed the robot very carefully and slowly near a grasshopper without letting the grasshopper flee,” said Prof Piotr Jablonski, a behavioral ecologist in the team at Seoul National University.
Write in Scientific reports, the researchers describe how grasshoppers were more likely to scramble when Robopteryx deployed its wings than when it did not. In the most effective displays, the robot swept them back and then swung down and forward. The insects fled more often when the researchers added white spots to the black wings, and when Robopteryx added large tail feathers to the display, they write.
Some grasshoppers inevitably hopped away when Robopteryx approached, but many would freeze or hide behind a plant stem and change position in preparation for escape. “In that situation, they are pretty well camouflaged and not as easy to spot as during a sudden jump,” Jablonski said.
The researchers suspect that coiling triggers ancient escapement circuit which is woven into the insect brain. The defense mechanism makes the grasshopper run, but once it is out in the open, it has a greater chance of becoming the predator’s lunch. If some feathered dinosaurs did hunt this way, the behavior could have driven the evolution of larger and stiffer feathers, they suggest.
However, other scientists may take convincing. Jablonski said the team faced “multiple rejections” from 11 journals before the study was reviewed and accepted for scientific reporting.
“I’m not so sure about this idea,” says Michael Benton, a professor of vertebrate palaeontology at the University of Bristol. “They are right that flight-type feathers arose in dinosaurs when they only had tiny wings that were too small for powered flight. However, these pin-like feathers are highly adapted to make an uninterrupted wing surface, and the first feathered dinosaurs may have used them to glide from spot to spot.
“People often say ‘half a wing is no use,’ but actually half a wing is what many modern gliding lizards and mammals have and it’s a good adaptation for unpowered flight or gliding.
