Abstract

Muscle-attachment impressions are described for the first time from representatives of the nautiloid suborders Oncoceratina (Oncoceras sp., Beloitoceras sp., Diestoceras sp.) Ascoceratina (Billingsites deformis (Eichwald)?, Discosorina (Parryoceras euchari Sweet & Miller), and Rutoceratina (Metacoceras sp.). Notes concerning the probable configuration of such impressions in certain Paleozoic Barrandeoceratina (Charactoceras?) and Triassic Lyroceratina (Proclydonautilus ursensis Smith) are included. Muscle-attachment impressions are not known in the Endoceratina and Actinoceratina; in known Ellesmeroceratina, Michelinoceratina, and secondarily straight Tarphyceratina (Lituitidae) the retractors were attached dorsally ("dorsomyarian"), whereas in described Barrandeoceratina, coiled Tarphyceratina, Ascoceratina, Oncoceratina, and Discosorina, these muscles were attached ventrally ("ventromyarian"). Described Rutoceratina, Nautilina, Solenochilina, and Lyroceratina are similar in that the retractors were attached laterally ("pleuromyarian"). In several cases, similar attachment patterns suggest adaptive convergence, rather than relationship, and their taxonomic significance is thereby reduced.

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