北海道北西部古丹別地域の上部白亜系大型化石層序

Abstract

The jaw apparatuses of three late Cretaceous desmoceratines (Tragodesmoceroides subcostatus, Damesites ainuanus, and D. semicostatus) are described and compared with those of other ammonites and modern cephalopods. The jaws of the three species morphologically resemble one another, and belong to the anaptychus-type jaws of Lehmann (1981), because of the fundamental jaw structures and the absence of a calcareous element. Based on comparison of jaw structures with modern cephalopods and the jaw-muscle relations in modern Nautilus, a possible buccal structure of the Desmoceratinae is proposed. -Author