Unusual findings of cephalopod jaws in Mesozoic shallow water sandy facies

Abstract

Jaws of fossil cephalopods, originally composed mainly of organic matter, are rare findings. They are sometimes can be found in nodules, in body chambers of their hosts (ammonoids and nautiloids), and in the fine-grained deposits, including Konservat-Lagerstätten. Findings of fossil coleoid jaws, which were completely organic and devoid of mineralized elements, are especially rare. Here, for the first time, numerous specimens of three-dimensional phosphatized cephalopod jaws, preserved in the extremely shallow-water coastal sandy facies of the Upper Jurassic (Volgian), Lower (Albian) and Upper Cretaceous (Cenomanian, Turonian, and Campanian), all of which have so far been widely considered only as a source of vertebrate fossils, are described. Both upper and lower cephalopod jaws were found, whereas lower jaw elements are more common. Most of the jaws were referred to as belonging to coleoids, judging by their shape and the ratio of the sizes of their outer and inner lamellae. The overall shape and rounded front tips of the lower jaws, as well as the relatively straight, not curved shape of the upper jaws suggest that they belonged to octobrachian coleoids. One of the jaws most likely belongs to a nautilid specimen. Some coleoid jaws from the Upper Cretaceous are relatively large, suggesting the large body size of their owners. It should be noted that elements of the jaw apparatus are the only remnants of cephalopods at most localities with coastal sandy facies. The study of these jaws sheds light on the diversity of cephalopods in coastal ecosystems of the Cretaceous time.