The problem with being an expert on dinosaur behaviour is that little can be inferred from the fossilised bones of beasts that died millions of years ago.
For researchers in South Korea, however, the absence of any living creatures to observe was merely another challenge to overcome. Enter Robopteryx, a robot that resembles – if one squints and ignores the wheels – the prehistoric, peacock-sized and fan-tailed omnivore, Caudipteryx.
The scientists built the machine to test their ideas about the origins 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 proposed all manner of benefits for small “proto-wings”. They might have worked as insect nets, prevented prey from escaping, allowed for long hops and gliding, and helped warm the animal and its newborn offspring.
An alternative hypothesis is that dinosaurs used their feathered appendages in threatening displays to flush insects and other prey from their hiding places. This “flush and pursue” strategy, put forward by the South Korean team, is used with great effect today in the northern mocking bird and greater roadrunner.
To test their hunch, the scientists put Robopteryx in front of unsuspecting grasshoppers and made it perform different wing and tail moves. These were designed to mimic displays Caudipteryx may have performed about 124m years ago in the early Cretaceous.
“We always very carefully and slowly positioned the robot near a grasshopper without startling the grasshopper to flee,” said Prof Piotr Jablonski, a behavioural ecologist on the team at Seoul National University.
Writing in Scientific Reports, the researchers describe how grasshoppers were more likely to scarper when Robopteryx deployed its wings than when it did not. In the most effective displays, the robot swept them back and then swooped them down and forwards. The insects fled more often when the researchers added white patches to the black wings, and when Robopteryx added large tail feathers to the display, they write.
Some grasshoppers inevitably hopped away as Robopteryx approached, but many would freeze or hide behind a plant stem and change their position in preparation to escape. “In that situation, they are quite well camouflaged and not as easy to spot as during a sudden jump,” said Jablonski.
The researchers suspect that flush displays trigger ancient escape circuitry that is woven into the insect brain. The defence mechanism sets the grasshopper running, but once out in the open, it has a greater chance of becoming the predator’s lunch. If some feathered dinosaurs did hunt in this way, the behaviour could have driven the evolution of larger and stiffer feathers, they suggest.
Other scientists, however, may take some convincing. Jablonski said the team faced “multiple refusals” from 11 journals before the study was reviewed and accepted for Scientific Reports.
“I’m not so sure about this idea,” said Michael Benton, a professor of vertebrate palaeontology at the University of Bristol. “They are right that flight-type feathers originated in dinosaurs when they just had tiny wings that were too tiny for powered flight. However, these pennaceous feathers are very much adapted to make an unbroken wing surface, and the first feathered dinosaurs may have used them in gliding 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 great adaptation for non-powered flight or gliding.”
