Original paper

Comparative morphology of modern and fossil coleoid jaw apparatuses

Tanabe, Kazushige

Abstract

Current knowledge about the jaw apparatuses (i.e. beaks or mandibles) of modern and fossil cephalopods is reviewed with special reference to those of coleoids. In modern cephalopods, the jaw apparatus is housed in the buccal mass and consists of articulated upper and lower jaws, which have a special function to bite and cut up a prey with the aid of the surrounding jaw muscles. Both the upper and lower jaws are composed mainly of a darkly tinted chitin-protein complex. The jaw apparatuses of extant coleoids are characterised by a posteroventrally elongated inner lamella in the lower jaw and the absence of a calcareous jaw element. These features are clearly distinguishable from those of nautilid jaws, which possess a substantially reduced inner lamella of the lower jaw and calcareous tips in both the upper and lower jaws. Recent discoveries of well-preserved jaws referable to vampyropod and possibly teuthid coleoids from the Late Cretaceous of the North Pacific fill the gap in the relatively poor fossil record of the Coleoidea; they clearly demonstrate that large non-belemnoid coleoids existed in this bioprovince together with ammonoids and nautilids.

Keywords

cephalopodacoleoideajaw apparatuscomparative morphology