<i>Nautilus</i> hard parts: a study of the mineral and organic constitutents

Abstract

The mineralized hard parts of Nautilus , including the mandibles, statoconia, and uroliths, are more complex with respect to ultrastructure, mineralogy, trace element, and isotopic composition than was previously recognized. X-ray diffraction and amino acid composition analyses of the organic structural hard parts (siphuncle tube, shell wall and septum organic matrix, mandibles, and muscle tendon sheath) show that two different chitin-protein complexes are utilized by Nautilus. The mandible mineral hard parts are particularly complex, with five different minerals present in various locations. A comparison of the statoconia of Nautilus species with the statoliths of dibranchian cephalopods reveals an evolutionary trend in which carbonate is substituted for phosphate. This study also shows that Nautilus uses a number of different crystal-forming processes for constructing its hard parts. The data presented here provide a broad spectrum of information, which, when applied to the fossil counterparts, can be utilized for improving our understanding of ancient nautiloid biology.