Rather, it is the chief ingredient of hollow struts in both upper and lower jaws, and these struts are concentrated in the areas of the jaws that bear down on prey. Summers cannot yet say how these struts form, but their function is clear. Without adding much weight to a structure, struts allow it to resist bending and buckling. Struts are a favorite tool of engineers, whether they are designing a bridge or a piece of corrugated cardboard. Likewise, struts help a cownose ray's jaws hold up against the shell of a clam or an oyster.
Ligaments hold the upper and lower jaws of the cownose ray tightly together.
For a shell caught in the middle, the resultant pressure would be shattering. But Summers suspects that the struts are responsible for only part of the cownose ray's shell-crushing ability. Species of rays that eat fish or soft-bodied invertebrates have loose ligaments connecting the upper and lower jaws. In these species, the jaws' left and right sides are separate, which means the ray can bite down with one while opening the other. That freedom gives these rays the flexibility they need to handle squirming prey.