Also found in: Dictionary.
the calcified tip of the upper jaw of extinct cephalopods. In rock, rhyncholites are found separately from the shells of these mollusks. Extinct nautiloids had rhyncholites that were similar in structure to the jaw tips of extant Nautilus. The origin of other rhyncholites has not been precisely established. They are known to have existed since the Triassic period. The most varied kinds of rhyncholites have been found in Jurassic and Cretaceous deposits.