A Nautilid Cephalopod Beak from the Lower Miocene Ichishi Group, Central Japan

Abstract

An isolated cephalopod beak was discovered in the Lower Miocene unit of the Ichishi Group at Iedokoro, Misato Village, Mie Prefecture, central Japan. It measures 39.7mm in maximum length and consists of large outer and short inner horny lamellae, with a conspicuous anterior calcified tip; the outer lamella is divided into a pair of posteriorly elongated wing portions. In the absence of the strongly convex, posteriorly elongated inner lamella that occurs in the upper beaks of all extant cephalopods, the present specimen is identified as the lower beak. The overall morphological features suggest a closer phylogenetic affinity to Recent Nautilus (Nautilidae) than to the coleoids, but the paired wing portions are more elongated than those of the lower beaks of Nautilus. We provisionally refer this cephalopod beak to the genus Aturia, because large mature shells of Aturia cubaensis occur in the same horizon.