Don't be afraid of the Robo-dinosaur, learn from it
The origin of bird wings has long puzzled paleontologists: why did these structures evolve in the age of the dinosaurs? And what were some of the earliest wings used for, if not to fly?
In research published Thursday in the journal Scientific Reportsscientists used a robot dinosaur and terrified locusts to argue that small feathered dinosaurs might have flapped wings early to flush out insect prey. Their proposal adds an explanation for why wings evolved before flight.
“It has been shown that the larger the wings, the more insects the birds catch and bring to the nest,” said Piotr Jablonski, an ornithologist at Seoul National University and author of the paper. “And when you see it in birds, you naturally think of dinosaurs.”
Feathers first evolved in dinosaurs as hairy bristles, most likely used for insulation and display, said Steve Brusatte, a paleontologist at the University of Edinburgh, who did not participate in the paper. Only one family of dinosaurs evolved streamer-like feathers, which eventually gave rise to wings and flight in modern birds. But researchers remain unsure whether such wings evolved to enable flight in an early lineage of dinosaurs or served some other purpose.
Adding to the puzzle is the presence of early protowings on flightless bird relatives such as Velociraptor and Oviraptor, said Minyoung Son, a paleontologist at the University of Minnesota and an author on the paper. Paleontologists have suggested several explanations, noting that even proto-wings give rise to animals extra maneuverability and enough lift to perform higher jumps. Others suggested they helped predators immobilize larger preyhelped incubate eggs or were a display for friends and rivals.
But wing displays can also target other species, said Dr. Jablonsky. Some modern birds flap their wings while hunting, revealing white spots or contrasting feathers that terrify hidden prey.
The strategy, known as flush-pursuit, takes advantage of the tendency of many insects to respond automatically to rapidly approaching shapes. The automatic response keeps them one step ahead of most predators. But wing displays by flush pursuers hack this system, causing the prey to run away too early. They reveal themselves and are eaten.
Many early winged dinosaurs were carnivores and insectivores, so Dr. Jablonsky and his colleagues wondered whether protowings might have evolved for a similar purpose. The team built 'Roboteryx', a black turkey-sized robot with the basic size and shape of Caudipteryx, a small omnivorous dinosaur from 124 million years ago.
Hyungpil Moon, an engineer at Sungkyunkwan University in South Korea and author of the study, said the simple robot was able to mimic flush chases. The team even gave the bobbled tail dramatic white bars, reminiscent of those found on Caudipteryx fossils.
The team unleashed Roboteryx on locusts, an insect with roots in the Mesozoic era that is susceptible to this hunting strategy in modern birds. When Roboteryx went outside with bare arms, said Jinseok Park, a graduate student at Seoul National University and a paper author, fewer than half of the locusts tested fled. But when the researchers added structures to the arms that resembled protowings, 93 percent of the locusts fled. The jumping insects also dispersed more often when striped tail feathers were added to the display.
The team argues that the effectiveness of protowings in deterring prey may have helped early winged dinosaurs reach greater heights. Successful flush chasers typically have adaptations in the areas of fast running, maneuverability and balance, said Dr. Jablonsky. The same wings that frightened insects also allowed rapid changes in pursuit speed and direction in small dinosaurs.
The new suggestion does not contradict or replace previous hypotheses, especially those related to the use of wings for signaling, Mr. Son said. Instead, the team suggests that the early development of a flush-pursuit strategy gave rise to mutually reinforcing adaptations that could help explain how flight began.
“This new study is one of the most imaginative and interesting I have seen, and provides some provocative new ideas,” said Dr. Brusatte. But while he admits that small early wings could have been used to deter prey, he's not sure if they evolved specifically for that purpose.
“In the end, this is like one of Kipling's 'Just So Stories,' about how the elephant got its trunk,” said Dr. Brusatte. “It's fun and compelling and even intuitive and rhetorically meaningful, but how do you prove that with fossils?”
Dr. Jablonsky responded that “almost every animal uses every structure in different ways. With this study we propose one element with which we can combine several elements.”
For Julia Clarke, a paleontologist at the University of Texas who was not involved in the paper, the study is a reminder of how multifunctional bird wings fall outside their role in flight.
“It reflects the true complexity of form-function relationships in the natural world,” said Dr. Clarke. “There is no reason why a 'half wing' should only have one function.”