Mironenko Aleksandr, Boiko Maxim, Bannikov Alexandre, Arkhipkin Alexander, Bizikov Viacheslav, Košťák Martin (2021) First discovery of the soft-body imprint of an Oligocene fossil squid indicates its piscivorous diet Lethaia, in press

Abstract

First discovery of the soft-body imprint of an Oligocene fossil squid indicates its piscivorous diet

The first well-preserved soft-body imprint of a fossil squid was discovered from the Lower Oligocene of the Krasnodar region, Russia. The squid is perfectly preserved, with many details of its body available for study, such as imprints of eyes and head, a pair of statoliths, jaws, and stomach contents. Statoliths of this squid are the first finds of in situ statoliths in fossil non-belemnoid coleoids, and their shape is characteristic of the genus Loligo (family Loliginidae). Although some Mesozoic coleoids were previously classified as teuthids, these finds remain controversial and the squid described herein is the first unquestionable representative of fossil Teuthida known to date. It should be noted that the squid is preserved not due to phosphatization, which is typical for fossil coleoids, but by pyritization and carbonization. Numerous fish remains in the stomach contents of the squid indicate its piscivorous diet. A small cutlassfish Anenchelum angustum, which was buried together with the squid and whose bones are located near the squid's jaws, sheds light on the circumstances of the death of this animal. Most likely, the squid suffocated in the anoxic bottom waters, where it drowned along with its last prey (distraction sinking).

Synopsis

This article is devoted to a unique specimen - the first undoubted imprint of the soft body of a fossil squid in the world. The specimen was found by an amateur paleontologist Vadim Kitain in the Lower Oligocene deposits of the Pshekha River, Krasnodar region, Russia and was donated to the Paleontological Institute of the Russian Academy of Sciences in Moscow. The imprint of the squid was preserved in sediments that were formed on the bottom of the sea basin under anoxic conditions. It should be noted that the soft tissues of the Oligocene squid were preserved due to pyritization and partly carbonization, but not phosphatization, as is usually the case with the tissues of fossil cephalopods. The imprint of the squid's body is excellently preserved: the head, eyes, jaws, mantle, stomach, rectum, the imprint of the ink sac and statoliths - aragonite stones from the equilibrium organs - are clearly visible. It was the shape of the statoliths that made it possible to determine the taxonomic affiliation of the squid –it belongs to the modern genus Loligo of the family Loliginidae even though it lived more than 30 million years ago.

The fact that Loliginids appeared at least in the Eocene (40 million years ago) was previously known due to the findings of separate statoliths with a characteristic shape, but no imprints of soft tissues had yet been found prior to our finding. The fossilized stomach and rectum of the squid are filled with fragments of fish scales and bones, which indicates the piscivorous diet of this mollusk. And the hunting of fish killed this specimen. The squid was found along side a small cutlassfish Anenchelum angustum, whose ribs are in contact with the squid's jaws, and the spine behind the head is fractured at a right angle, which is typical of victims of modern squid attacks. It is most likely that the squid pierced the fish's swim bladder and drowned with this fish and sank into the bottom layers of water, where there was a deficit of oxygen. Due to this lack of oxygen, the squid gradually died, holding its last meal in its arms.

Keywords

Coleoidea, Loliginidae, Loligo, Oligocene, squids, statoliths, Teuthida

Links