Scientists at Brown University and Harvard University have realized that birds have an independent ligament at the shoulder joint, which can keep their wings stable during flight. In the electronic preview of Nature, they explained how this tough organization evolved into a key element of bird flight. "How do animals fly from the ground? Or how did the upper limbs evolve into wings? This is a fascinating question. " David Bayer, a postdoctoral researcher in the Department of Ecology and Biological Evolution at Brown University, who led the research team, said, "Our research found that a single ligament played an increasingly important role in the evolution of birds." Bayer and his research team focused on the shoulder joint of birds, because it is at the shoulder joint that the powerful force of muscle aggregation is released. Why don't birds dislocate their shoulder joints during flight? Or what keeps the wings stable in flight? Bayer and his research team have conducted extensive research on this in a unique way. They studied living animals and dinosaur fossils respectively, and also studied the interaction between the bone force acting on the shoulder joint and the aerodynamic soft tissue. The first research object of the research group is chicken. In order to better understand how birds stabilize their wings during flight, the researchers drew a three-dimensional "virtual skeleton" map by using the computer X-ray axial layered contrast scanning technology, and calculated the force needed to maintain a stable flight posture. They found that the key part to keep pigeon wings stable is neither scapula nor muscle, but coracoid-brachial ligament. Coracoacromial ligament is a short ligament connecting the humerus and shoulder of birds, which can balance all the forces released by the shoulder joint-from the tension of pectoralis major muscle in birds' chest to the wind thrust under birds' wings, which is the key to modern birds' flight. In order to find out whether the coracoid-brachial ligament of ancient animals played the same role in shoulder balance, the research team also studied the alligator. Alligators are close relatives of birds and all are branches of ancient lizards (or ancestors). 250 million years ago, ancient lizards appeared on the earth. They used to be the "main reptiles" on the earth, and then gradually evolved into the dominant dinosaurs in Mesozoic. Therefore, alligators are a very important starting point to understand the whole evolutionary process. In the laboratory of Farisi Jenkins, a professor of biology at Harvard University and director of the Museum of Vertebrate Paleontology, scientists put three alligators on an electric treadmill and filmed them with X-ray video. Bayer and Steven Gatsey, an evolutionary biologist at Brown University, used these videos to create a three-dimensional cartoon that accurately showed the dynamic position of the crocodile's shoulders when walking. They found that alligators use muscles instead of ligaments to support their shoulders. Next, Bayer found the fossil record of Archaeopteryx from the stone case and studied the skeleton of Archaeopteryx, which many paleontologists think is the earliest bird on earth. Bayer even went to Beijing to study the fossil remains of Confucius Bird, Young's Chinese Bird-like Dragon and Millennium Chinese Bird-like Dragon recently discovered in China. They are close relatives of modern birds. If the coracoid-brachial ligament is the key to the flight ability of birds, Bayer hopes to find evidence in Archaeopteryx. Surprisingly, however, it seems that this new force balance system based on ligaments evolved gradually among Mesozoic flying animals. "This means that the flying organs of birds have improved over time," Bayer said. "Our research shows that early birds are different from modern birds in maintaining shoulder balance when flying, so their flying methods may be different from modern birds. Some scientists think they fly from trees to the ground by gliding, or fly off the ground by flapping their wings. The methods we use in studying this power balance system can help us to test these theories. | More