First Discovery of the Soft‐Body Imprint of an Oligocene Fossil Squid Indicates Its Piscivorous Diet

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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 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 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, represented 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 Institute of RAS) on the Pshekha river by the deepwater origin of Teuthida that prevented their amateur paleontologist Vadim Kitain in 2014. If the fossilization in shelf deposits (Arkhipkin et al. 2012). arguments of the ‘Octobrachia hypothesis’ are valid, If all finds of ‘fossil teuthids’ belong to Octobrachia, this finding represents the first known teuthid in the there is not a single fossil record of teuthid soft tis- fossil state. The shape of statoliths enabled to identify sues in Mesozoic and Cenozoic layers, contradicting belonging of this fossil teuthid to the family Lolig- to the genetics (molecular clock) data pointing out to inidae and genus Loligo. The circumstances of its co‐existence of Decabrachia (including teuthids) with death and the features of taphonomy are also Octobrachia since Late Jurassic. Moreover, two finds discussed. LETHAIA 10.1111/let.12440 First discovery of the soft‐body of a fossil squid 3

Geological setting cutlassfish A. angustum (Danil'chenko 1980) (family Trichiuridae). The squid was found in the basal layers of the Lower Maikop deposits (Khadum, Pshekha Forma- tion; Rupelian, nannoplankton zone NP 21) which Material and methods are outcropped on the right bank of the Pshekha River at Gorny Luch farmstead, Apsheronsk district, The specimen is housed in the Borissiak Paleontolog- Krasnodar region, SW Russia (N44.335°, E39.808°; ical Institute of the Russian Academy of Sciences Fig. 1), and overly light marls and argillaceous lime- (PIN RAN, Moscow) with collection number PIN stones of the Belaya Glina Formation (regional 5817. The imprint of a squid body is preserved on × state) (Priabonian). The lower part of the Pshekha the surface of siltstone slabs (24 22 cm in size) – № Formation is composed of an alternation of dark and consists of two parts the main imprint ( PIN № grey weakly calcareous clays and light grey clays; the 5817/1, see Fig. 2) and its counterpart ( PIN 5817/ thickness of the interlayers varies from a few mil- 2). Details of the squid anatomy are visible on both limetres to several centimetres. Dark grey layers are slabs. micro‐ and thin‐bedded and contain a lot of organic The main specimen and its schematic interpreta- carbon and many planktonic pteropods of the gen- tion are shown in Figure 3. The imprint consists of era Vaginella and Limacina (Popov et al. 2019) distinct contour of the mantle, funnel, head with sta- (Planorbella layers of Danil'chenko 1960, 1967), as toliths and large eyes, arm stubs with the beak and ‐ well as skeletons of various fishes, algae and remains buccal mass. The animal was embedded dorso of terrestrial plants. Light grey clay layers are not ventrally, in a straight horizontal position. The man- laminated and usually do not contain macrofossils; tle is apparently cylindrical in the anterior half and – however, flattened shells of sea urchins (Spatan- conical in the posterior half. The length of the visi- goida, Schizaster sp.) can be occasionally found ble part of the mantle is about 100 mm; the length of there (Solovyov & Bannikov 2015). Features of the the head from the mantle to the beak is 25 mm. distribution of organism remains and the nature of Therefore, the total visible length of the specimen is fi the rock indicate that the dark grey clay layers cor- about 125 mm. The apical end of the body and ns fi respond to the anoxic environment at the bottom of are not preserved. It can be assumed that the ns the basin (hydrogen sulphide contamination), while could have been slightly elevated above the sediment the light grey layers indicate an oxygened bottom during the burial, and thus missing in the imprint. A condition. At least 75 fish species are known from pair of aragonitic statoliths is also well preserved in the Pshekha Formation of the Eastern Paratethys the head of the squid, and their length is 1.8 mm and (Bannikov 2010), among them the clupeids Rupelia width 0.9 mm (Fig. 4). Although the length of the rata strongly predominate; Anenchelum angustum, preserved part of the mantle is only 100 mm, the total Palaeogadus spp. and Protobrotula sobijevi are also length of the squid mantle, judging from the size of very common and indicate the normal salinity and the statoliths and the visible position of internal – subtropical climate in this site during the Early Oli- organs, was about 140 150 mm. For this calculation, gocene. Remains of the terrestrial plants and fishes we have used the relationship between the total length such as the Syngnathidae and Champsodontidae of the statolith and mantle length of the loliginid suggested relative proximity to the coastline, proba- squid Doryteuthis gahi from Arkhipkin & Roa (2005). bly islands. The width of the front end of the squid mantle is Geological and fossil features of deposits described 27 mm. The length of the deep imprint of the ink sac above indicated that the early Maikop beds on Pshe- with an ink duct is 20 mm, the maximum width of kha River were formed relatively close to the shore in the ink sac is 5.5 mm, but the ink mass is not pre- fi a warm sea basin with alternating anaerobic and aer- served. The fusiform mass of sh bone remnants, × obic conditions at the bottom. The absence of deep‐ which is 16 1.5 mm, is located in parallel with the sea fishes at the site of the squid discovery indicates a ink sac and its duct (Fig. 5A). Most likely, this is the ‐ relatively small thickness of habitable water column content of the rectum. Much larger irregularly drop fi (probably the shelf). Above the outcrop, bathypelagic shaped mass of sh bones and scales with dimen- × fish appear, indicating a deepening of the basin. sions of 15 9.5 mm is located closer to the poste- The squid was found in a dark grey laminated clay rior end of the imprint (Fig. 5B). Undoubtedly, this fi layer (which was formed under anoxic/hypoxic con- is the stomach content. The presence of sh rem- ditions) together with the skeleton of the relatively nants in the stomach indicated the squid was feeding small (presumably young) predatory mesopelagic shortly before its death. 4 Mironenko et al. LETHAIA 10.1111/let.12440

Fig. 1. Map of the Pshekha River at Gorny Luch farmstead locality, Apsheronsk district, Krasnodar region, SW Russia (N44.335°, E39.808°).

Fig. 2. Field photograph of the squid specimen on a river bank. The ﬁsh skeleton is partially covered in rock layers. Photo by Vadim Kitain.

The head is 25 mm long, 21 mm wide. In the in front of the beak, the neural spines and dorsal‐fin squid's head, the eyes are perfectly preserved, with a pterygiophores are located under the beak (Fig. 5C). visible dimension of 17 × 10 mm. Spherical lenses The total length of the fish from the tip of the skull (approximately 5 mm in diameter) are visible in the to the caudal fin is about 225 mm, the length of the centre of each eye. The beak is small, its sharp dark fish skull is 30 mm. At a distance of 34 mm from the rostrum protrudes anteriorly from the centre of the skull, the vertebral column is broken at a right angle, arms crown. Since the squid is embedded in the slab towards the imprint of the squid (Fig. 5D). ventral side up, the lower jaw is visible, whereas the The squid's arms are preserved only as short stubs upper jaw is hidden in the rock. The base of the beak radiating anteriorly from the buccal mass. Due to is embedded into a dark elongated buccal mass. poor preservation, the number of arms is uncertain. The squid is associated with the cutlassfish A. an- Most likely, the arms were wrapped around the body gustum (Danil'chenko 1980) of the family Trichiuri- of the fish and thus located outside the bedding dae. Its vertebral column is in a couple of millimetres plane. There are no hooks or sucker rings in the LETHAIA 10.1111/let.12440 First discovery of the soft‐body of a fossil squid 5

Fig. 3. Anatomy of the squid specimen (based on the field photo, see Figure 2). A, general view. B, schematic sketch of the squid. B – beak, bm – buccal mass, ey – eyes, g – gladius, h – hyponome, is – ink sac, l – eye lens, m – mantle, r – rectum, sl – statolithes, st – stomach. Scale bar – 2 cm. sediment around fish skeleton in front of squid head, central part of the slab with the front part of the so either they were very thin and did not preserve, squid's head was accessible for this analysis due to or were initially absent (which we consider less the large size of the slab. The large mass of porous probable). clay made it impossible to achieve an acceptable vac- The position of both statoliths indicated that the uum quality, which made it difficult to obtain high‐ squid was embedded in the slab with its ventral side quality SEM‐images. We considered cutting the spec- up. The wide triangle contour of the squid body pro- imen unacceptable in order to keep it intact for truding from the mantle to the level of posterior future research. However, we were able to take an margins of eyes, apparently corresponds to the fun- image of the squid's jaw with bones of the fish nel. The gladius is visible in the anterior third part of (Figs. 5C, 6). Moreover, Energy‐dispersive X‐ray the mantle as a faint dark contour appearing at the spectroscopy (EDX) analysis of the squid's head and anterior mantle margin, gradually widening posteri- surrounding clay was performed. EDX analysis orly and disappearing at the level of the ink sac showed the presence of aluminium and silicon in the (Fig. 3). specimen, which are likely associated with the com- The large size of the slab with a squid imprint and position of the clay particles of the sediment. The its high fragility greatly complicates the study of this soft‐body imprint of the squid also contains carbon, finding. The specimen was examined using a Tescan sulphur and iron, whereas phosphorus is completely Vega II scanning electron microscope, but only the absent (see Fig. 7, Table 1). 6 Mironenko et al. LETHAIA 10.1111/let.12440

C D

Fig. 4. Squid statoliths. A, B and D – statoliths of the Oligocene squid. A, right statolith (on the left side of the specimen since it is located with ventral side up). B, left statolith (on the right side of the specimen). C, statolith of modern loliginid squid Doryteuthis gahi. D, sketch of the statolith (based on B), DD – dorsal dome, LD – lateral dome, RO – rostrum, SF – statolith fissure (If the fissure is not filled with the wing material, that means that this statolith belonged to a juvenile/young squid, which is the case herein), W – wing. Scale bars 0.5 mm.

tapered into an obtuse ventral end. The rostral angle Discussion is obtuse, close to 160–170°. The overall shape of the statolith is quite similar but more elongated with a Taxonomic position longer rostrum than those of Loligo valeriae from the Lower Pliocene deposits of Jamaica (Clarke & Fitch The overall shape of the body and head of the squid 1979). These statoliths are also different by having a is characteristic to a species of the family Loliginidae. much rounder rostrum tip instead of a pointy ros- It is likely that this specimen belongs to the genus trum tip as observed in fossil Loligo statoliths Loligo judging from the shape of its well‐preserved described from the Lower Miocene deposits of the statoliths. Each statolith has a wing which is not fully Southern Aquitanian Basin in France (Clarke et al. formed and contains a fissure between the wing and 1980). the statolith body. These features are characteristic to Other anatomical features of the imprint such as the young and immature recent Loligo squid (see the overall shape of the body and head, the presence Arkhipkin 2003). Both statoliths are situated in the of an elongated conical mantle, a wide funnel, large posterior area of the head, exactly at the place where eyes with a lens, an arm crown with short stubs of the statocysts are located in living specimens. Unfor- rather slender arms and a vague contour of the glad- tunately, both statoliths lay posterior surface up, ius anterior part – are consistent with loliginid affilia- meaning that the anterior surface and spur have not tion of this specimen. been possible to analyse. The lateral dome is smooth, with almost rectangular dorsal end. The dorsal dome is undeveloped (characteristic to immature squid), Fossil teuthids and the challenge of their and it is not separated from the lateral dome by a interpretation groove, making the dorsal edge of the statolith Coleoids with the gladius (a partly or completely almost straight. The rostrum is rather short and decalcified shell without a phragmocone) usually LETHAIA 10.1111/let.12440 First discovery of the soft‐body of a fossil squid 7

C D

Fig. 5. Details of the specimen. A, imprint of the ink sac (the ink duct in the lower left corner) and the rectum, infilled with fish fragments. B, stomach contents, consisting of fish bones and scales. C, head of the squid with eyes, bases of arms and jaws. Note the position of the fish skeleton in front of the jaw. D, broken vertebral column of the fish. Scale bars for A and B – 5 mm, for C and D – 1 cm.

Fig. 6. The location of the squid beak and fish bones. A, SEM image of the beak and fish bones, scale bar is 1 mm. B, explanatory drawing by the SEM image. termed as ‘fossil teuthids’ first appeared in fossil according to the widely accepted ‘Octobrachia records in the Middle Triassic (Schweigert & Fuchs hypothesis’, all ‘fossil teuthids’ belong to the Octo- 2012), soon after the hypothetic divergence datum brachian coleoids while teuthids (squids) are absent between Decabrachia and Octobrachia estimated in fossil records (see, e.g. Young & Fuchs 2012). The using molecular clock data, and reached greatest similarity of gladii of some representatives of subor- diversity in Jurassic – Cretaceous, during Mesozoic ders Prototeuthina, Loligosepiina and Teudopseina marine revolution (Kröger et al. 2011; Tanner et al. with modern teuthids is considered to be the result 2017). As the shell reduction and development of of convergence (Fuchs & Iba 2015). decalcified gladius occurred independently and Close affinity of all ‘fossil teuthids’ to Octobrachi- repeatedly in different Coleoid lineages (Bizikov ans rather than to Decabrachians is based on the fol- 2004, 2008), it seems logical to assume that so‐called lowing facts: all soft bodies of ‘fossil teuthids’,even ‘fossil teuthids’ may include representatives of both extraordinarily well‐preserved, never show more than Octobrachian and Decabrachian clades. However, eight fossilized arms, some of them exhibit an 8 Mironenko et al. LETHAIA 10.1111/let.12440

Fig. 7. EDX data of the elemental composition. Note the lack of phosphorus among the chemical elements.

Table 1. EDX data of the elemental composition. between the arms that were interpreted as Octo- brachian filaments (modified arms of the 2nd pair). Chemical element Weight % Atomic % However, this interpretation is not fully consistent C 13.73 20.17 with the photo of the specimen (Klug et al. 2021a O 57.21 63.09 fig. 3) showing that supposed ‘filaments’ are located Mg 0.90 0.65 Al 4.94 3.23 externally from 3rd pair of arms on both sides of the Si 13.48 8.47 head, but not in the place where the filaments should S 3.49 1.92 be located: between the 1st and 3rd pair of arms. On K 1.25 0.56 ‘fi ’ Ca 2.60 1.15 both sides of the head, the laments look like short Fe 2.24 0.71 fragments of some modified arms and their interpre- Zn 0.15 0.04 tation either as Octobrachian filaments (2nd pair of arms) or some distal parts of Decabrachian tentacles (4th pair of arms) on this specimen is difficult to umbrella‐like web between the arms, uniserial suckers prove. without a sucker stalk or horny rings, lateral cirri on On the contrary, the stellate arm imprints of eight the arms and an additional (second) pair of fins, arms left by Plesioteuthis (Brown & Vokes 1944; octopod‐like beaks and Vampyroteuthis‐like mantle‐ Donovan & Fuchs 2016; Fig. 3) do not prove that gladius interaction (Bandel & Leich 1986; Engeser this coleoid lacked tentacles. Comparisons with 1988; Donovan & Fuchs 2016; Fuchs et al. 2016). recent squids (e.g. Doryteuthis (Loligo) pealleii However, both Octobrachian and Decabrachian (Lesueur 1821)) actually show that when the squids coleoids originally had eight normal arms and two explore the bottom selecting a place for depositing modified arms: in Octobrachia, the second pair of eggs, they do it with their arms and not with tenta- arms is modified into tactile filaments (in extant cles. The latter are retracted and concealed within Octobrachia, these filaments remain only in the arm crown. Therefore, the only number of arms Vampyroteuthis) while in Decabrachia the fourth is not operational in ‘fossil teuthids’ and it has to be pair of arms is modified into retractable tentacles considered in combination with other morphological that may be concealed inside pouches in the base characteristics. of the arm crown. While the arms sometimes were Other ‘Octobrachian’ characters described in ‘fos- preserved in ‘fossil teuthids’, modified arms (fila- sil teuthids’ represent most likely common ple- ments or tentacles) have much less preservation siomorphic character state for both Decabrachia and potential and until recently have never been found Octobrachia rather than specific characters of Octo- in fossil records. brachia (Naef 1928; Boletzky 1982, 1992; Young & Recently, Klug et al. (2021a) described an excep- Vecchione 1996; Lindgren et al. 2004). Some of these tionally preserved specimen of Jeletzkyteuthis coriacea characters are present in different groups of modern from the Early Jurassic (Toarcian) Posidonienschiefer Decabrachia. For example, cuttlefishes and squids Formation (Germany) with remains of four rather have protective membranes on the arms and tenta- symmetrically arranged arm pairs and two narrow cles supported by trabecular that are homologous to and elongated, transversely striated structures cirri; an interbrachial web is developed in squid LETHAIA 10.1111/let.12440 First discovery of the soft‐body of a fossil squid 9 families Histioteuthidae, Bathyteuthidae and Spiruli- Clarkeiteuthis conocauda were described with bony dae; additional pair of fins present in representatives fishes Leptolepis bronni in their arms (Jenny et al. of recent squid families Grimalditeuthidae, Chiro- 2019). A similar coleoid‐fish association which is teuthidae, Joubiniteuthidae, Bathoteuthidae and composed of belemnoid B. antiquus and an Mastigoteuthidae. Summing up, it can be concluded unknown bony fish, clutched in the coleoid arms, that the systematic position of so‐called ‘fossil was recently described from the Callovian Oxford teuthids’ (Prototeuthidina, Loligosepiina and Teu- Clay Formation in the UK (Hart et al. 2020, fig. 8). dopseina) is still not reliably defined. A more in‐ In all these cases, Jurassic coleoids were buried under depth review of these groups is advisable, involving anoxic conditions and it has been suggested that morphology of the hard structures (the shell, sta- their death was caused by asphyxiation as they sank toliths). As an additional tool, the criteria proposed down into anoxic deep waters after a victim's swim- by Bizikov (2004, 2008) for homological analysis of ming bladder was pierced (Jenny et al. 2019). Associ- the shell in Coleoidea can also be used. ated dismembered fish remains are also known in the The largest morphological variability is seen in Santonian Palaeoctopus (Incirrata) from Lebanon Teudopseina, in which the closest similarities to (Woodward 1883; Fuchs et al. 2009); however, in this teuthid gladii are still not well explained. Especially, case the fish is located not in the arms of the mollusc. the family Enchoteuthidae – for example Upper Cre- The cases mentioned above (with the exception of taceous genera Tusoteuthis and Niobrarateuthis pos- Palaeoctopus) can be considered as examples of ‘dis- sess gladius characteristics (particularly the cross‐ traction sinking’. This term means that an animal (or section of the rachis) highly similar to some Recent animals) was too pre‐occupied with some process decabrachians (Nicholls & Isaak 1987; Larson 2010). (feeding or copulation) to notice that it was sinking Nevertheless, Larson (2010) pointed a different char- into the hypoxic bottom waters of the basin and acter of the conus and its connection to rachis. faced suffocation (Mapes et al. 2019). Another great Another record of an incomplete gladius of genus example of ‘distraction sinking’ in cephalopods was Eoteuthoides (Upper Turonian) is putatively referred recently described: there are two octobrachian to family Muensterellidae (Fuchs 2020). However, coleoids, larger J. coriacea and smaller Parabelopeltis the gladius shows some apomorphies to the Recent fexuosa, which were buried together, with the tail of family Promachoteuthidae (Košťák 2003). Neither in the smaller specimen trapped in the arms of the lar- enchoteuthids nor in Eoteuthoides, the number of ger (Klug et al. 2021a). Most likely, Jeletzkyteuthis arms is virtually known. The gladius composition in hunted Parabelopeltis, caught it and sank into the enchoteuthids might be originally chitinous (Larson hypoxic bottom waters during feeding. It should be 2010); in Eoteuthoides, the gladius is secondarily noted that Jeletzkyteuthis, as well as Oligocene lolig- composed by francolite. Therefore, the Mesozoic inid squid, has no hooks on its arms, but that didn't teuthid records are still doubtful, respectively stop it from keeping the prey even after death. unknown. Coleoids are not the only animals affected by the dis- The only post‐Mesozoic coleoid gladius record is traction sinking. Similar examples are known for known from the Oligocene of Hungary (Kretzoi Eocene turtles, which died in pairs during copulation 1942). Based on detailed morphological investigation (Joyce et al. 2012) and for ammonoids – Late Missis- of newly re‐discovered specimen, Necroteuthis hun- sippian Metadimorphoceras and Upper Jurassic garica has recently been assigned to loligosepiid lin- (Tithonian) Lingulaticeras, which also were pre- eage with a separate suborder Vampyromorphina served in pairs, in aperture‐to‐aperture position (Košťák et al. 2021). Thus, the Oligocene specimen of (Mapes et al. 2019). However, referring the last Loligo (PIN № 5817) described herein represents the example to distraction sinking raises doubts: in both first and unambiguous teuthid record worldwide. cases, ammonoids in pairs are same‐sized and in the case of Jurassic Lingulaticeras both belong to the Circumstances of death same sex, making hypotheses of predation or copulation highly unlikely. Since there is good reason to The Oligocene squid studied is associated with the believe that ammonoids were semelparous and had cutlassfish A. angustum, located in front of its head, died in mass after spawning events (Landman et al. in the arms area, in contact with the jaws (see Figs 5 1996), individuals of the same size and sex could C, 6). It seems unlikely that this association is acci- have clung to each other in agony, as modern Arg- dental and more likely that the fish represented the onauta octopuses or some squids sometimes do, last meal of the squid. Some fossil coleoids died along dying after spawning (Nesis 2005). with the fish that were their last prey. For example, It can also be hypothesized that the Oligocene four specimens of Jurassic diplobelid belemnoid squid died after distraction sinking due to 10 Mironenko et al. LETHAIA 10.1111/let.12440 asphyxiation in anoxic deep waters with its prey in studied locality. Apparently, such incidents were the arms. However, there are some difficulties with rare, whereas coleoid cephalopods that became a this interpretation. First of all, Jurassic coleoids prey of any predators were occasionally preserved in Clarkeiteuthis and Belemnotheutis are armed with a fossil state – for example belemnite rostra, coleoid arm hooks, which could have continued to hold the beaks in stomachs of ichthyosaurs, plesiosaurs, pray even after the death of the molluscs. Loliginids hybodontid sharks and others (Böttcher 1989; Wild have no hooks and their keeping prey after death 1994; Wahl 2012) as well as coleoid hooks of belem- looks less likely, although not impossible, as we can nites, belemnoteuthidids, phragmoteuthids, etc.in see in the example of Jurassic Jeletzkyteuthis (Klug vertebrate coprolites and fish precoprolites/cololites et al. 2021a), which also has no hooks. In addition, (Přikryl et al. 2012). young specimens of modern loliginids (this specimen is probably immature) prefer to hunt crustaceans Preservation of the studied squid specimen and fishes which are much smaller than their own size, whereas the length of this fish is equal or even Clements et al. (2017) argued that due to the high larger than the length of the squid. On the contrary, content of ammonium chloride ions in the tissues examples of juvenile loliginids hunting for fish of the of modern squids, phosphatization of the soft bod- same size are described (Alvarez Perez & Zaleski ies of these coleoids is unlikely whereas not neces- 2013, fig. 10.4D) and cutlassfish A. angustum are sarily impossible. Due to this, researchers suggested long, but very thin and slender. Modern cutlassfish that the tissues of ancient teuthids most likely could often become a prey of loliginid squids (Gasalla et al. have also not been phosphatized. Phosphatization is 2010; Pierce et al. 2013). The stomach content of the the main type of preservation of soft‐bodied marine squid studied herein contained numerous fragments animals including coleoids, in all currently known of fish scales and bones, and leaves no doubt that the Konservat‐Lagerstätten localities, such as Jurassic piscivorous diet was common for this squid at least Posidonia Shales, Oxford Clay Formation, Solnho- in the last days of its life. A fish bone is also located fen Plattenkalks, etc., their bodies are phosphatized under the jaw of the squid (Figs 5C, 6), making it (Donovan & Fuchs 2016). Soft tissues of ammo- impossible to imagine such a coincidence. nites, such as their mantle and muscle fragments It also should be noted that the fish which is asso- (Mironenko 2015; Klug et al. 2021b) and siphuncle ciated with the Oligocene squid is juvenile and its blood vessels (Tanabe et al. 2000; Mironenko 2017), vertebral column is broken at a short distance are also replaced with phosphatic minerals, behind the head (see Fig. 5D). The exact same inju- although the preservation of ammonite bodies is ries are typical for victims of Jurassic Clarkeiteuthis usually incomplete, with very rare exceptions (Klug (Jenny et al. 2019). Modern squids also often kill et al. 2021b). fish by biting their vertebral column shortly behind The Oligocene squid described has no signs of the head (Nesis 2005). The specimens of A. angus- phosphatization, that is confirmed by elemental anal- tum with a vertebral column broken in the same ysis of the specimen using the method Energy‐ place, shortly behind the head, were repeatedly illus- dispersive X‐ray spectroscopy (EDX) (see Fig. 7). trated from the coeval and close geographically Judging by the presence of sulphur and iron, the locality in Belaya River (Capasso & Bannikov 1997: imprint could have been formed by pyrite or by car- fig. 1; Monsch & Bannikov 2011: fig. 14a); however, bonization of the tissues. According to our knowl- until now these fractures were considered as post‐ edge, carbonization of ancient coleoid bodies has mortem and their occurrence was explained by never been reported with the exception of separate compaction of the sediment (Monsch & Bannikov chitinous elements such as jaws or hooks (e.g. Fuchs 2011). Taking into account the position of fish & Hoffmann 2017) or small tissue fragments skeletons in this locality, strictly along horizontal (Doguzhaeva & Summesberger 2012). However, car- layers of sediment, it seems most likely that broken bonization is a very common type of preservation of vertebral columns could be the result of successful Cretaceous and Cenozoic feathers, especially in predation of the squids. lacustrine and coastal marine environments (Davis & Therefore, whereas it is difficult to say why the Briggs 1995). Therefore, it gives us hope that another squid with no hooks did not get rid of the fish when carbonized teuthid imprints will also be found in the it got into anoxic conditions, the version of its sink- Mesozoic and Cenozoic coastal marine localities. It ing into anoxic deep waters together with fish with a cannot be ruled out that the chemical composition of pierced swimming bladder looks to be quite likely. the deposits also influenced the preservation of the The death of the squid as a result of an accident imprint. It has been shown that soft tissue can be bet- explains the extreme rarity of such finds at the ter preserved in clays with a high aluminium and LETHAIA 10.1111/let.12440 First discovery of the soft‐body of a fossil squid 11 silicon content (Forchielli et al. 2014; McMahon Part I. Myopsid squids, 301–321. Nova Science Publishers, Hauppauge. et al. 2016; Anderson et al. 2018; Naimark et al. Anderson, R.P., Tosca, N.J., Gaines, R.R., Koch, N.M. & Briggs, 2020). The EDX analysis of the specimen studied D.E. 2018: A mineralogical signature for Burgess Shale–type herein shows a relatively high content of these ele- fossilization. Geology 46, 347–350. Arkhipkin, A.I. 2003: Towards identification of the ecological life- ments (see Fig. 7, Table 1), so it is quite possible that style in nektonic squids using statolith morphometry. Journal in this case they really contributed to fossilization of of Molluscan Studies 69, 171–178. the soft body. Arkhipkin, A.I., Bizikov, V.A. & Fuchs, D. 2012: Vestigial phragmocone in the gladius points to a deepwater origin of squid (Mollusca: Cephalopoda). Deep Sea Research Part I: Oceano- graphic Research Papers 61, 109–122. Conclusions Arkhipkin, A.I. & Roa, R. 2005: Identification of ontogenetic growth models for squid. Marine and Freshwater Research 56, 371–386. We have described the first discovery of a fossilized Bandel, K. & Leich, H. 1986: Jurassic Vampyromorpha (di- squid from the Lower Oligocene deposits of Krasno- branchiate cephalopods). Neues Jahrbuch für Geologie und Paläontologie‐Monatshefte 3, 129–148. dar Region (North Caucasus, Russia). Judging by the Bannikov, A.F. 2010: Fossil vertebrates of Russia and adjacent shape of the well‐preserved statoliths and by the gen- countries. Fossil acanthopterygians fishes (Teleostei, Acan- eral outline of the body, the studied squid belongs to thopterygii), 244 pp. GEOS, Moscow [in Russian with English summary]. the family Loliginidae, to the genus Loligo. Therefore, Berthold, T. & Engeser, T. 1987: Phylogenetic analysis and sys- it is confirmed that loliginids already had existed in tematization of the Cephalopoda (Mollusca). Verhandlungen the Oligocene, as was previously assumed on the des Naturwissenschaftlichen Vereins Hamburg 29, 187–220. fi Bizikov, V.A. 2004: The shell in Vampyropoda (Cephalopoda): basis of the study of separate nds of statoliths. The morphology, functional role and evolution. Ruthenica Supple- studied squid hunted fish, as evidenced from its ment 3,1–88. stomach content, which consists of scales and frag- Bizikov, V.A. 2008: Evolution of the Shell in Cephalopoda, 444 pp. fi VNIRO Publishing, Moscow. ments of sh bones. The squid is not fully grown and von Boletzky, S. 1982: Developmental aspects of the mantle com- most likely died by drowning together with its last plex in coleoid cephalopods. Malacologia 23, 165–175. prey, the young mesopelagic cutlassfish A. angustum, von Boletzky, S. 1992: Evolutionary aspects of development, life- style, and reproduction mode in incirrate octopods (Mollusca, by the same way as previously described Jurassic Cephalopoda). Revue de Suisse Zoologie 4, 755–770. diplobelid belemnoid C. conocauda which drowned Böttcher, R. 1989: Über die Nahrung eines Leptoptery- along with their prey. It seems possible that the skele- gius (Ichthyosauria, Reptilia) aus dem süddeutschen Posi- donienschiefer (Unterer Jura) mit Bemerkungen über den tons of A. angustum, previously recorded from the Magen der Ichthyosaurier. Stuttgarter Beiträge zur Naturkunde same sediments with a vertebral column broken (B) 155,1–19. behind the head are the result of the successful hunt- Brown, B. & Vokes, H.E. 1944: Fossil imprints of unknown ori- fl ' gin: further information and a possible explanation. The Amer- ing of loliginid squids. The at imprint of the squid s ican Journal of Science 242, 656–672. body is preserved in great detail due to carbonization Capasso, L. & Bannikov, A. 1997: Vertebral anomaly in Anenche- or pyritization, in a fine‐grained sediment under lum angustum (Teleostei, Trichiuridae) from the lower Oligo- fi cene of the North Caucasus, Russia. Journal of Paleopathology anoxic conditions. 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