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(also horny tooth). (1) A conical horny cutaneous formation in some vertebrates that fulfills the functions of a true tooth. Epidermal teeth are found in cyclostomes (on the walls of the buccal funnel and on the tongue), the larvae of tailless amphibians (on the lips), and many cyprinoid fishes (on the anterior half of the jaws). The epidermal teeth of cyprinoid fishes replaced true teeth in the process of historical development. The epidermal teeth of lampreys and amphibians apparently are also of secondary origin.
(2) A horny formation of cornified epidermis characteristic of the embryo of some reptiles (tuatara, turtles, crocodilians) and birds. The epidermal tooth, which is located on the upper or lower jaw, is used for piercing the shell of the egg. Hence, it performs the same function as the egg tooth of lizards and snakes.