New insights into the buccal apparatus of the Goniatitina: palaeobiological and phylogenetic implications

Abstract

Exceptionally well-preserved radulae and lower jaws found both inside the body chamber of Cravenoceras fayettevillae (Mississippian) and in isolated nodules (Mississippian and Pennsylvanian) were analysed using CT scan and synchrotron propagation phase-contrast tomography. This approach reveals new anatomical details allowing us to investigate wear, preservation and muscle insertion in the buccal mass of the Goniatitina. For comparison, Recent cephalopod radulae were also investigated. The radula in the Goniatitina consists of nine elements per row, and its morphology is conservative in the group. The shape of the teeth is similar to that in some Recent coleoids. The lower jaw is morphologically closer to that of Recent Nautilus, consisting of a wide outer lamella and a reduced inner lamella. The morphology of the inner lamella reflects the outer lamella in smaller dimensions and does not protrude posteroventrally. The space between the inner and outer lamellae allows for muscle insertion. Our morphological data indicate that a mosaic of characters is present in the buccal mass of Goniatitina with some parts of the buccal mass being more primitive than others. This implies that different parts of the buccal mass may have followed different evolutionary histories.