Abstract
A b s t r a c t: The present state of knowledge concerning the function of anaptychi, aptychi, and opercula of ammonoids is reviewed. The jaw apparati found associated with the lytoceratid genera Gaudryceras and Tetragonites by KANI~ et al. (1978) and TANABE et al. (1980) and classified as rhynchaptychus type of ammonoidjaws by L~HMANN (1981) are re-interpreted. Morphologically, they are very similar to Nautilus jaws. Their interpretation as allochthonous nautiloid jaws is discussed and considered probable. However, beccublast cell impressions in Gaudryceras and recent Nautilus differ considerably. Further investigations are deemed necessary concerning a) the nature of the anaptychi in Palaeozoic anaptychus assemblages, whether they are opercula or jaw elements; b) the function of the laevaptychi. Their jaw nature is still open to doubt; c) the autochthony of the rhynchaptychus-type lower jaws found in lytoceratid Upper Cretaceous ammonites in Japan.
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