Cephalopod beak

All extant cephalopods have a two-part beak, or rostrum, situated in the buccal mass and surrounded by the muscular head appendages. The dorsal (upper) mandible fits into the ventral (lower) mandible and together they function in a scissor-like fashion.^[1][2] The beak may also be referred to as the mandibles or jaws.^[3] These beaks are different from bird beaks because it crushes bone while most birds don't.

Fossilised remains of beaks are known from a number of cephalopod groups, both extant and extinct, including squids, octopuses, belemnites, and vampyromorphs.^{[3][4][5][6][7][8][9]} Aptychi – paired plate-like structures found in ammonites – may also have been jaw elements.^{[10][11][12][13]}