Anchiornis's wrist bone was so wedge-shaped that it could fold its arms to its sides, keeping its arm feathers off the ground as it walked.
近鸟龙的腕骨呈深楔形，因此它可以将前肢折叠到身体两侧，行走时前肢上的羽毛可以悬空，不会拖在地面上。
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By decomposing fold and thrust systems into superposed detachment systems, it is possible to simulate extremely complex wedge structures and to do animation of the evolution of the structures.