First discovery of the soft‐body imprint of an Oligocene fossil squid indicates its piscivorous diet ALEKSANDR A. MIRONENKO , MAXIM S. BOIKO, ALEXANDRE F. BANNIKOV, ALEXANDER I. ARKHIPKIN, VIACHESLAV A. BIZIKOV AND MARTIN KOŠŤÁK Mironenko, A. A., Boiko, M. S., Bannikov, A. F., Arkhipkin, A. I., Bizikov, V. A., & Košťák, M. 2021: First discovery of the soft‐body imprint of an Oligocene fossil squid indicates its piscivorous diet. Lethaia, https://doi.org/10.1111/let.12440. 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 previ- ously 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 Anenche- lum 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). □ Coleoidea, Loliginidae, Loligo, Oligocene, squids, statoliths, Teuthida. Aleksandr A. Mironenko ✉ [[email protected]], Geological Institute of RAS, Pyz- hevski Lane 7 Moscow 119017, Russia; Maxim S. Boiko [[email protected]], Alexan- dre F. Bannikov [[email protected]], Borissiak Paleontological Institute of RAS, Profsoyuznaya 123 Moscow 117647, Russia; Alexander I. Arkhipkin [aarkhipkin@fisheries.gov.fk], Fisheries Department, Bypass Road Stanley FIQQ 1ZZ, Falkland Islands; Viacheslav A. Bizikov [[email protected]], Russian Federal Research Institute of Fisheries and Oceanography, Verkhnyaya Kras- noselskaya 17 Moscow 107140, Russia; Martin Košťák [[email protected]], Institute of Geology and Palaeontology, Faculty of Science, Charles University, Albertov 6 Praha 2 128 43, Czech Republic; manuscript received on 19/02/2021; manuscript accepted on 14/05/2021. Coleoids, cephalopod molluscs with an internal and – are known as ‘fossil teuthids’ from several more or less reduced shell, originated in Carbonifer- Konservat‐Lagerstätten localities, from the Middle ous (Donovan 1977; Kröger et al.2011).Later,they Triassic to Upper Cretaceous. Usually, their finds are diverged into two evolutionary branches: the first is connected to anoxic/hypoxic layers and are repre- the ten‐armed Decabrachia Haeckel, 1866, repre- sented by isolated phosphatized (francolite) gladii sented by fossil belemnoids and living teuthids that are quite variable in shape and structure. Soft (squids), cuttlefishes (Sepiida and Sepiolida), and spir- tissues of these ‘fossil teuthids’ including the mantle, ulids (Spirulida), and the second is the eight‐armed internal organs, fins and head with arms are rare but Octobrachia Haeckel, 1866 (=Vampyropoda Boletzky, not unique (Donovan & Fuchs 2016). Three major 1992) consisting of the Octopoda (Leach, 1817) and suborders are currently recognized within ‘fossil Vampyromorpha, with the only living species Vampy- teuthids’ based on the gladius morphology: roteuthis infernalis (Clements et al.2017).According Loligosepiina Jeletzky, 1965, Prototeuthidina Naef, to molecular clock data, this divergence occurred in 1921 and Teudopseina Starobogatov, 1983. the Middle Permian (Kröger et al. 2011; Tanner et al. The systematic position of ‘fossil teuthids’ has not 2017). Teuthids and other living decabrachians are yet been convincingly resolved, despite many efforts. estimated to have diverged in the Late Jurassic and For a long time, these coleoids were thought to therefore must have co‐existed with octobrachians belong to Teuthida, based on the resemblance of since late Mesozoic (Kröger et al. 2011; Warnke et al. their shell with the gladii of different groups of recent 2011; Clements et al. 2017; Tanner et al., 2017). squids (Naef 1922; Jeletzky 1966; Donovan 1977; Well‐preserved Mesozoic fossilized coleoids with Starobogatov 1976, 1983; Teichert 1988). The simi- partially or completely decalcified shell – the gladius larity in shape of the gladii of Jurassic and Cretaceous DOI 10.1111/let.12440 © 2021 Lethaia Foundation. Published by John Wiley & Sons Ltd 2 Mironenko et al. LETHAIA 10.1111/let.12440 genera such as Dorateuthis and Plesioteuthis with the of coleoid upper jaws in the Turonian of Japan, one gladii of modern squids of the family Ommastrephi- of which is attributed to Teuthida, indicate that the dae allowed researchers to consider them as direct teuthids have already existed in the Late Cretaceous ancestors and descendants (Donovan 1977; Luck- (Tanabe et al. 2006). ender & Harzhauser 2004; Bizikov 2008). On the In the fossil state, not only the soft tissues of contrary, Bandel & Leich (1986) were the first to note coleoids and their internal shells are preserved, but that the soft‐body morphology of ‘fossil teuthids’, also the statoliths – small aragonite concretions found when present, indicate their affinity to Octobrachia in the equilibrium organs of coleoid cephalopods (sta- rather than Decabrachia. tocysts). The oldest known statoliths were found in As more data on ‘fossil teuthids’ soft‐body anat- the Early Jurassic (Hettangian) deposits of Germany omy were published (e.g. Haas 2002; Fuchs et al. (Schwarzhans 2018). Unfortunately, statoliths are 2003, 2007, 2013; Fuchs 2006; Klug et al. 2015; usually found in the Jurassic and Cenozoic deposits Donovan & Fuchs 2016), it was shown that all the separately from fossilized bodies and the shells of finds of the Mesozoic ‘fossil teuthids’ exhibited only coleoids and this fact significantly complicates their eight arms and, furthermore, some of them have affinities to host animals. Statoliths from the Middle such octobrachian characteristics as umbrella‐like Jurassic (Callovian) of Great Britain were tentatively interbrachial web between the arms, uniserial suckers interpreted as belonging to belemnitids Belem- without sucker stalk and horny rings, lateral cirri on notheutis antiquus (Hart et al. 2015). Statoliths were the arms, absence of nuchal cartilage (despite cepha- found in situ in the cephalic region of the Upper lic cartilage preservation), octopod‐like beaks, addi- Jurassic belemnitid Acanthoteuthis from Germany tional (second) pair of fins (Bandel & Leich 1986; (Klug et al. 2016); however, due to their poor preser- Engeser 1988; Donovan et al. 2003; Donovan & vation, it was not possible to relate them with other Fuchs 2016; Fuchs & Larson 2011; Fuchs 2020). Ten separate finds known from the Jurassic deposits. unequivocal arms were described to date only for fos- Undisputed teuthid statoliths are known only sil belemnoids, but not for the ‘fossil teuthids’ (Ban- from the Cenozoic deposits. Several hundred coleoid del & Leich 1986; Donovan et al. 2003; Fuchs et al. statoliths from North America and Europe including 2003, 2007, 2013; Fuchs & Weis 2008, 2009; Fuchs & Eocene, Oligocene, Miocene, Pliocene and Pleis- Larson 2011a,b; Arkhipkin et al. 2012; Klug et al. tocene specimens have been described to date 2015; Donovan & Fuchs 2016). Hence, the ‘Octo- (Clarke & Fitch 1979; Clarke & Maddock 1988; brachia hypothesis’ according to which all ‘fossil Clarke & Hart 2018; Neige et al. 2016). They can be teuthids’ belong to the extinct side branches of the matched to those of living squid families and genera, early Octopodiformes Berthold & Engeser, 1987, such as Loligo, Dosidicus, Sthenoteuthis, Moroteuthis while the teuthid coleoids are completely absent in and Berryteuthis (Clarke & Fitch 1979; Clarke & the fossil record, was proposed and became widely Maddock 1988; Clarke & Hart 2018). The oldest accepted (Fuchs & Larson 2011a; Fuchs 2016; Fuchs Cenozoic statoliths which are known to date are the et al. 2016; Sutton et al. 2016). Currently, the subor- formal species Loligo applegatei Clarke & Fitch 1979 der Prototeuthidina is placed within the superorder from the Ypresian (Eocene) and Loligo mississippien- Octobrachia; the suborder Loligosepiina is placed sis Clarke & Fitch 1979 from the lower‐middle Oligo- within the order Vampyromorpha Robson, 1929; the cene, both of which belong to the genus Loligo. suborder Teudopseina is placed within the order Therefore, judging by the finds of statoliths, Lolig- Octopoda Leach, 1817 (Fuchs & Weis 2008). Lack of inidae is the oldest known squid family. finds of identifiable soft tissues of true teuthids in the This paper describes the first find of a well‐ fossil record seems very strange, but one of the possi- preserved imprint of the soft body of a fossil squid ble explanations may be a high concentration of with in situ preserved statoliths from the Oligocene ammonia in their soft tissues, which possibly could deposits. It was found during the field work under have inhibited the phosphatization process (Cle- the leadership of A.F. Bannikov (Borissiak Paleonto- ments et al. 2017). Another reason could be possible logical