In any group, not everyone can be a fearsome Tyrannosaurus rex or a majestic Triceratops. Someone must be stuck being gangly and awkward, with stubby little dodo wings that never fly, only flap.
That was the sad tale of Caudipteryx, a three-foot-long dinosaur that lived about 125 million years ago in what’s now China. To the modern eye, Caudipteryx looks like a miniature ostrich but with a longer, fan-tipped tail and, remarkably, even dinkier wings—like a sparrow’s flappers stuck onto a turkey. The wings are actually so puny that paleontologists are compelled to tackle the evolutionary puzzle of why they exist at all.
“We are trying to get at ‘What’s the use of half a wing?’” says Minyoung Son, a Ph.D. student in paleontology at the University of Minnesota. “A full-size wing that could at least glide would make sense. But we have this fossil evidence for dinosaurs with what we would call half a wing.”
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Ideally, an enterprising paleontologist would conduct behavioral experiments, but that’s a tall order. “You can’t really go out there and capture a dinosaur with half a wing,” Son says. “Building a robot was the second-best thing we could possibly do.” The result is new research published on January 25 in Scientific Reports, in which Son and other scientists describe experiments they conducted using a robotic Caudipteryx model that the team dubbed Robopteryx.
The robot incorporated nine motors, arranged to mimic the joints paleontologists see in Caudipteryx fossils. Then the researchers ornamented the basic Robopteryx to mimic different would-be wings—comparing bare arms with “proximal proto-wings” (think arms with feathery armpits) and “distal proto-wings,” in which feathers occur only at the tips of the arms, like fingers.
Next, it was time to run some experiments inspired by dinosaurs’ distant descendants: birds. Piotr Jablonski, a field biologist at Seoul National University and a co-author of the new research, has studied birds his whole career and has long been intrigued by a behavior called a flush display.
Select birds such as Northern Mockingbirds (Mimus polyglottos) conduct flush displays by abruptly spreading their wings or tails, typically showing off colorful patterns, to startle tasty insects out of their hiding places. Jablonski wondered whether the stubby wings of Caudipteryx may have allowed the little dinosaur to use flush displays as a hunting tactic—and whether the behavior may have facilitated the development of full-fledged wings.
The Robopteryx team tested their robot’s various proto-wing displays against a modern grasshopper species, Oedaleus infernalis. These insect are appealing as test prey because scientists have mapped their nervous system, so the researchers could watch the animals’ neurons respond to Robopteryx’s displays. And just as the team had predicted, the grasshoppers were most likely to panic when they were confronted by the robodino adorned with proto-wings at the ends of its arms.
The scientists suggest that these findings support the idea that dinosaurs might have used primitive wings to startle prey. The behavior works because insects aren’t smart enough to calibrate their responses to different predators: while automatically executing a dramatic jump is a valuable technique to evade many predators, it isn’t effective against those that use flush displays. Jablonski bluntly describes the fate of grasshoppers in that scenario: “They are actually flying into their own death,” he says.