A phosphatized cephalopod mouthpart from the Upper Pennsylvanian of Oklahoma, U.S.A.

概要

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An exceptionally well-preserved cephalopod mouthpart was discovered in a phosphate concretion from the lower Missourian (Upper Pennsylvanian) in Tulsa, Oklahoma, U.S.A. It consists of an almost complete jaw apparatus and a radula, both of which are in the living orientation. The black upper and lower jaws, preserved as phosphate, were probably chitinous. The lower jaw is slightly larger than the upper and is characterized by a widely open outer lamella. The upper jaw is built up of a large outer lamella and a short, scallop-shaped inner lamella; the former is distinctly divided into two portions in the posterior region. The radula is preserved in the anterior portion of the buccal cavity ; it is made of more than ten rows of teeth, each consisting of seven tooth elements with a pair of marginal plates. The overall features of the jaws and radula are essentially similar to those described in association with ammonoids rather than nautiloids and coleoids, suggesting that this mouthpart can be referred to the Ammonoidea. However, the lower jaw in our specimen differs from previously described mandibles of Carboniferous Gastrioceratoidea, Neoglyphioceratoidea, Gonioloboceratoidea, and Dimorphoceratoidea in its less elongate outline. For this reason, we refer the cephalopod mouthpart to the Ammonoidea other than the above superfamilies with reservation.
日本古生物学会の論文
2001-12-31