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A young ostrich springs up on a Chinese farm. His bobs neck, his legs pumping – and the artificial wings attached to his back beating up and down.
Alas, this ostrich will not fly. He replaces another creature tied to the earth, a dinosaur called Caudipteryx. Some 125 million years ago, this theropod walked on two legs and wore a pair of feathered 'proto-wings', similar to the dummy ones worn by the ostrich. Recently, researchers undertook to study the extinct creature for a long time while she was facing one of the biggest controversies of paleontology: the first evolution of avian leakage.
In a study published Thursday in PLOS Computing Biology, a team consisting of mechanical engineer Jing-Shan Zhao and several paleontologists used the ostrich equipped – as well as mathematical and robotic models – to assert that when Caudipteryx worked, his mini-wings were beating involuntarily. The researchers finally proposed that the descendants of the dinosaur have exploited this trait and removed it from the soil for the first time.
Other experts are not convinced, saying that the analogs of the study do not do justice to the complexity of the animal he is supposed to study. But the disagreement itself highlights the unresolved nature of the debates on the evolution of the flight of the inhabitants of the world.
"You'd be hard-pressed to find a palaeontologist who does not have an opinion," he said. Armita Manafzadeh, a doctoral student at Brown University who did not participate in the study.
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Because modern birds have evolved from a particular lineage of dinosaurs, theropods, researchers are turning to them to understand how the flight began. Some defend a "top-down" theory, claiming that winged dinosaurs have learned to fly by climbing trees and sliding on branches, such as flying squirrels. Others are on the ground side, claiming that the dinosaurs ran up and flapping their wings. Still others challenge the dichotomy itself, claiming that the two theories do not exclude each other.
For their entry into the fray, Dr. Zhao's group performed three experiments. All focused on Caudipteryx, a useful organization to study "the evolution of the first dinosaur to the modern bird," said Dr. Zhao, a professor at Tsinghua University in Beijing. Caudipteryx was discovered in China in the late 1990s and, in rendering, it often looks like an edgy and edgy chicken.
For the first experiment, the group used fossil analyzes to develop a simplified mathematical model of the dinosaur. They then simulated a running movement in the legs of the model and calculated the reaction of the other parts of the body. They found that very quickly – between 5.5 and 12.9 miles per hour, a range within the estimated capacity of Caudipteryx – the wings of the model were beating.
For the second test, they built a robo-Caudipteryx and performed it on a treadmill. Here too, they observed constant oscillation, even as they increased and decreased wing length.
Then it was time to do a live test. Mr. Zhao and his colleagues built a harness with force sensors and a set of wings. They increased many birds, including ducks and geese, before settling on the six-month ostrich presented in the video.
"His height and weight were similar to those of Caudipteryx," said Dr. Zhao. (Because living dinosaurs are not available for paleontology studies, their descendants, partridge babies with chicks with prosthetic tails often serve as proxies.)
While the ostrich was running, the beats were obvious and the sensors measured a small amount of lift: the movement offset some of the body's weight of the bird. Dr. Zhao suggests that Caudipteryx might have noticed that the strange thing his wings were doing made him easier to run and leaned over. In this way, the passive crush provided "basic training for a later flight," he said.
Is it conclusive proof that the beat came first? Other researchers, although impressed by the three-part approach to the study, expressed doubts.
Dennis Voeten, who studies flying dinosaurs at the European Synchrotron Radiation Facility in France and the Swedish University of Uppsala, believes that the group's conclusions have gone too far. Observing the oscillations "does not prove that this dynamic" entailed "the first feathered dinosaurs to perform a flapping motion similar to that of a bird," he said. Ms. Manafzadeh added that the simplification of the anatomy of dinosaurs presents pitfalls, as does the use of passive plastic wings to replace active limbs.
Dr. Zhao replied that the advantages of the beat should have been sufficient to guide evolution in this direction and that the group's experiments left room for various anatomical considerations.
"You can change the mass, or the stiffness of the muscles, anything," he says. "The beat movement will not change."
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