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Non-avian dinosaur and bird fossils are frequently found in a characteristic posture consisting of head thrown back, tail extended, and mouth wide open. The cause of this posture—often called a "death pose"—has been a matter of scientific debate.
A study conducted by Alicia Cutler, Brooks B. Britt, and colleagues from Brigham Young University in Provo, Utah, suggests that the pose is a result of submersion in water after death. Seconds after placing chicken carcasses in water, the bodies assumed the "death pose." The reduction of friction to allow ligaments and tendons to contract to their typical positions causes dorsoflexion of the head and tail of the animal. They also found that the chickens' claws contracted, likely due to the same cause (reduction of friction in water allows ligaments to return to their original positions, and death releases muscle tension that would have held the neck and claws in different positions in life). The experiment was replicated with an emu, which produced the same results. When the intervertebral ligaments of the chickens' necks were cut, they did not assume the death pose.