An Early Triassic gladius associated with soft tissue remains from Idaho , USA — a squid-like coleoid cephalopod at the onset of Mesozoic Era

We describe an Olenekian (Early Triassic) “fossil squid” belonging to the oldest complex Mesozoic marine biota collected in the Lower Shale unit of the Lower Triassic Thaynes Group in Idaho, USA. The studied specimen shows a tapered structure embedded in a cylindrical soft body. Morphological, ultrastructural and geochemical features of the specimen suggest that it corresponds to an internally-shelled cephalopod exhibiting a tapered micro-laminated gladius with rachis, narrow median and lateral fields and a large conus; a pair of posterior large fin-supported cartilages and fins; ventral and dorsal mantle band-shape structures, the dorsal one being cartilaginous; mantle patches; a stomach containing undigested arm-hooks and sheet-like pieces of potential flooded ink. Coupled SEM/EDS analyses show that (i) arm-hooks and ink were pseudomorphed by nanoparticles (less than 0.6 mm in diameter) of carbon, (ii) gladius and soft tissues were substituted by granules of calcium phosphate, (iii) cartilage canalicula’s were partially filled with calcium phosphate grains and crystals of Znand S-containing minerals. The specimen was hence probably fossilized due to metabolism of Pand C-accumulating bacteria. Based on this specimen, Idahoteuthis parisiana Doguzhaeva and Brayard gen. et sp. nov. and Idahoteuthidae Doguzhaeva and Brayard fam. nov. are erected. This family is characterized by an elongated, cylindrical, dorsally cartilaginous muscular mantle; well-developed, about 0.2 mantle length, rounded anteriorly and acute posteriorly, fin-supported cartilages and similarly shaped two fins at conical mantle termination, and thin slender gladius with narrow median and lateral fields, rachis and breviconic conus. This family assumedly falls in Myopsida (Decabrachia). A streamlined body, large fin-supported cartilages and eroded arm-hooks in the stomach of Idahoteuthis Doguzhaeva and Brayard gen. nov. suggest that this was a maneuverable cannibal predator that dwelled in the subequatorial shallow sea of the west coast of Pangaea.


Introduction
A ~250.6 Myr-old middle Olenekian (= early Spathian, Early Triassic) complex marine ecosystem named the Paris Biota, has been recently discovered in southern Idaho, USA (Brayard et al. 2017).One of the most intriguing specimens of this exceptional fossil assemblage is represented by an elongated structure interpreted as a coleoid gladius associated with soft tissues (Brayard et al. 2017: fig. 4G).This gladius is the oldest one that reveals similarities to gladii of some extant coleoid taxa and therefore it can serve as a basis to propose a new scenario on the evolutionary development of a gladius.Based on this specimen, Idahoteuthis parisiana gen.et sp.nov.and Idahoteuthidae Doguzhaeva and Brayard fam.nov.are erected and their systematic position is analyzed.The preservation of the non-biomineralized structures, a gladius, arm-hooks and sheet patches of a potential ink in the stomach, mantle and fin-supported cartilages, as well as the position of this coleoid in the Early Triassic food web are also discussed.

Geological setting
The gladius specimen comes from the Lower Shale unit of the Lower Triassic Thaynes Group, west of the city of Paris, Bear Lake County, southeastern Idaho, western USA (Fig. 1; Brayard et al. 2017: figs. 1-4).This unit is represented by alternating limestone and shale beds, which were deposited during the middle Olenekian in the shallow Western USA Basin.This epicontinental sea was connected to the Panthalassic Ocean to the west and located at a near equatorial position on the western margin of Pangaea (Fig. 1).Exposures containing this specimen are approximately 20 m thick and consists of mainly grey to blue, thin-bedded silty limestone, deposited in a distal upper offshore environment on a very flat platform.The early Spathian (base of the middle Olenekian) ammonoid Tirolites abundantly occurs throughout these exposures (Brayard et al. 2017).A radiometric age of about 250.6 Mya (i.e., only about 1.3 Mya after the end-Permian mass extinction) is assigned to the immediately overlying Middle Limestone unit and was obtained from the coeval Tirolites-Columbites beds in South China (Galfetti et al. 2007;Jenks et al. 2013).

Material and methods
The studied specimen is ca.48.7 mm long and ca.7.4 mm large fossil embedded in a compact silty limestone split into two slabs (Figs.2A, 3).The specimen is compressed because of compaction and deformed according to original differences in morphology and composition observed between its anterior, middle and posterior parts (Figs. 2,3).This specimen displays non-biomineralized structures, the original dislocation and symmetry of which may be changed.Romano et al. 2013) with position of the studied specimen.Ammonoid zonation after Jenks et al. (2013) and Jattiot et al. (2016).Stratigraphy follows the main units defined by Kummel (1954).Radiometric ages after Galfetti et al. (2007) and Burgess et al. (2014).Abbreviations: LL, Lower Limestone; LS,Lower Shale; ML, Middle Limestone; MS, Middle Shale; UCS, Upper Calcareous Siltstone.Considering its tapered end (Figs.2A, 3) as indicating the anterior part, the specimen is exposed on its left side (Fig. 2A).The tapered end is likely folded and compressed due to compaction (Figs.2A, 3).The middle part of the left side of the gladius is removed that allows to see the material beneath (Figs. 2A,C,4).The middle part of the specimen is cylindrical in shape (Fig. 2A); one side (dorsal; at the top on pictures) being more straight and less deformed than the opposite one (ventral; at the bottom on pictures).The latter shows a wavy outline indicative of elastic soft tissue deformations (Fig. 2A).The posterior end of the specimen shows a flattened triangular structure (Fig. 2) and a pair of pear-like structures with a metallic luster (Fig. 2A).At the anterior end of the specimen (Fig. 2A 1 ), an uncertain organic structure distantly resembling longitudinally fractured coleoid-type jaws is present (see Doguzhaeva et al. 2007b: figs. 11 The specimen was studied using a Nikon S522249 light microscope and a Wild M400 light photomicroscope.Ultrastructural and elemental analyses were carried out by means of a Scanning Electron Microscope Hitachi-4300 equipped with an energy dispersive spectrometer (EDS) at the Swedish Museum of Natural History in Stockholm.Ultrastructures were examined under magnifications up to 70 000, using a gold coating .Elemental analyses (SOM: table 1, Supplementary Online Material available at http://app.pan.pl/SOM/app63-Doguzhaeva_etal_SOM.pdf) were performed at an accelerated voltage of 15 kV, and we used energy calibration as measured on standard minerals of known accuracy.EDS analyses were made on several points of each morphological structure and matrix (SOM: table 1).All elements were analyzed and no peak was omitted.The contents of the elements are given in per cent to total weight.

Results
Morphology and ultrastructure.-Thestudied specimen shows the following structures; their initial location and symmetry may have been modified because of various potential postmortem deformations.
Gladius: The total length of the exposed part of the gladius is 42.2 mm, and the total preserved length of the fossil is 48.7 mm.The actual length of the gladius is likely longer as the length of the rachis (a free continuation of the median field) is incomplete (Figs.2A 1 , 3).The gladius is slender, tapered, with three narrow longitudinal areas (median and lateral fields), a rachis, and a relatively long conus that is ~0.15% of the gladius length (without the rachis) (Fig. 2A 1 ).The gladius structure exhibits five preserved parts: (i) a short piece of a broken rachis, (ii) an anterior tapered part (Figs.2A, 3), (iii) a dorsal, thin longitudinal fracture between the tapered part and the end of the conus (Fig. 2A), (iv) a conus (Fig. 2), and (v) a displaced tiny ~3 mm long fragment of an apical part (Fig. 2C).It shows three narrow fields that are broadly rounded anteriorly; the median one being slightly longer than lateral fields (Fig. 2C 2 ).The gladius is thinwalled, micro-laminated, non-biomineralized and may have been constituted by chitin (Fig. 9C).
Fin-supported cartilages: These are large, about 0.15% of the gladius length, paired, pear-like structures adjacent to the conus (Fig. 2A).They are formed by a canalicular cartilage (Bairati et al. 1987) characterized by a well developed matrix and the canalicular network made of canals with individualized walls 8A).
Fins: These are ~10 mm long, partially preserved paired non-biomineralized structures located near the posterior end of the conus.They surround the pear-shaped canalicular cartilages.They are ~0.2 of the preserved length of the specimen (Fig. 2A).
Stomach: This structure corresponds to a large, oval, fractured sac located in the central part of the specimen, close to its ventral side (Fig. 2A).It exhibits a lighter color than the surrounding material and provides access to numerous inclusions.The stomach shows a broken folded edge on its ventral side, excepting on the posterior part where it adjoins a preserved fragment of the band-like mantle structure that may have protected it.The stomach is, however, not broken dorsally and laterally.It contains diverse, supposedly undigested hard remains as well as soft tissue debris; about ten arm hooks and tiny black sheet patches of ink material are identified (Figs. 4,9A,B,D,F).For comparison, the stomach described in the Late Cretaceous "fossil squid" Dorateuthis contains undigested fish remains (Lukeneder and Harzhauzer 2004).
Arm-hooks: These are found accumulated in the stomach (Fig. 4) and are not observed around the specimen.They are ~2-2.4mm in maximum size (distance between the distal end of the basement and the acute tip of the hook), black, compressed, fractured, eroded, and lack of typical luster.They have a relatively long and thick basement and display a nearly straight, thick shaft inclined towards a strongly curved and long hook (for comparisons see Rieber 1970;Kulicki and Szaniawski 1972;Engeser and Clarke 1988;Doguzhaeva et al. 2007a: fig. 6.6;Doguzhaeva et al. 2007c: figs. 2B, C, 5A;Doguzhaeva et al. 2010a: figs. 6, 8;Doguzhaeva et al. 2010b: figs. 6A-E, 9C, D).
Ink: Despite the fact that the ink sac is not preserved, potential flooded ink is irregularly disseminated in the specimen as tiny pieces of black sheets (Figs.4A, 9A, B).Similar black sheets of flooded ink were observed in some specimens of the Late Triassic coleoid Phragmoteuthis, while some other specimens show flask-shape ink sacs (Doguzhaeva et al. 2007c: figs. 2A, 3B, C).The patches of black sheets were especially identified in the stomach.Like the armhooks, they consist of carbon micro-granules (Fig. 9A) (for comparison see Doguzhaeva et al. 2004 Bite marks: These marks are rounded or oval, irregularly spaced pits about 1-2 mm in diameter largely observed in the conus (Fig. 2A 2 , B 1 , C 1 ).
The uncertain organic structure: This structure consists of dark chitinous laminas (Fig. 2A

Original composition and fossilization of the specimen (SEM/EDS data).-Gladius:
The gladius shows a microlaminated ultrastructure (Fig. 9C) and is uniformly dominated by calcium phosphate: calcium is about 20-28%; phosphorus is 3-13%, oxygen is 35-50%, and carbon is 10-17% (SOM: table 1).At some places, the gladius is weakly silicified (silicon is up to about 2%) and contains antimony (up to 8%), iodine (about 3%) and sodium, platinum, and magnesium (less than 1%).The gladius lacks sulfur and iron (SOM: table 1).This chemical composition points towards a diagenetic phosphatization of chitin, which is in living coleoids also micro-laminated (Doguzhaeva and Mutvei 2006: figs. 4A-G, 5B).Chitinous fossil gladii have been the place for fossilization processes mediated by phosphorus-accumulating bacteria, which enhance the preservation of gladii as phosphatized pseudomorphs (Doguzhaeva and Mutvei 2003), especially in anoxic paleoenvironments (see Weaver et al. 2011).An experimental study on the microlaminated pen of Loligo showed that an alkaline treatment changes porosity, wettability, swelling and the crystalline packing of β-chitin by means of intercalation of water mole-cules between the chitin laminas (Ianiro et al. 2014).Similar ways of degradation of the studied gladius may have preceded its diagenetic phosphatization.
Matrix adjoining the gladius: The matrix shows values of carbon similar to those of the gladius (about 17%) while the oxygen content is slightly higher (63% against 51%) and the maximum values of phosphorus are twice lower than in the gladius (about 6% against 13% in the gladius; SOM: table 1), potentially indicating differential fossilization and diagenetic pathways.Calcium is highly variable (4-23%) but its highest values are only slightly lower than in the gladius (about 28%).Silicon maximum values are five times higher than in the gladius.Potassium, sodium, and sulfur, which are absent in the gladius, are detected in the matrix but values remain anecdotal (less that 1%).Antimony and iodine are slightly lower in the contacts than in the gladius in the matrix but values remain anecdotal (7% and 2% against 8% and 3%, respectively).The composition of the matrix adjoining the gladius was thus probably in situ poorly influenced by the decay of soft tissues.
Arm-hooks: They are uniformly dominated by high carbon content (about 70%).Oxygen is about 25%, calcium 3%, and chromium 1% (SOM: table 1).This composition points towards a fossilization by means of carbonization.The carbonization of arm-hooks was previously reported in the Late Triassic Phragmoteuthis (Doguzhaeva et al. 2007c).The differing composition of the observed chitin structures, like the gladius and the arm-hooks, may result from minor variations of their original chemical composition, as well as the potential different packing of the chitin sheets and the crystalline packing of β-chitin.This observation agrees with the micro-granules of carbon found in the Late Triassic Phragmoteuthis, which are smaller in the arm-hooks than in the gladius suggesting some ultrastructural differences (Doguzhaeva et al. 2007c).
Ink: Observed potential ink tiny patches show high content of carbon (up to about 46%) and oxygen (up to about 44%), and low content of calcium (up to 6%), phosphorus (up to 3%), titanium (up to 3%), and sulfur (about 2%) (SOM: table 1).Therefore, the ink (originally melanin) was fossilized by means of carbonization, like the arm-hooks.The ink is the only substance showing a peak of titanium.This may correspond to observations in vivo on melanin from coleoid ink, which absorbs heavy metals (Chen et al. 2009).
Overall, the SEM/EDS analyses (SOM: table 1) highlight the main diagenetic processes responsible for preservation of the organic matter-rich structures; they are: (i) phosphatization of the gladius, cartilages, mantle, stomach mass and soft tissue debris, (ii) zinc-sulfur mineralization of the canalicular system in fin cartilages, and (iii) carbonization of arm hooks and ink.In addition to zinc, the absorption of heavy metals such as platinum, mercury, and titanium occurred during the fossilization of the non-biomineralized structures (SOM: table 1).The observed differential soft tissue preservation could result from the combined effects of the metabolism of anaerobic P-, C-, and S-accumulating bacteria and seawater potentially characterized by a high  Remarks.-At the juvenile stage, the gladius is narrow, with three narrow fields each of which shows a broadly rounded anterior outline (Fig. 2C).The median field is slightly lon- Idahoteuthis parisiana Doguzhaeva and Brayard sp.nov.
Description.-Theholotype is a 48.7 mm long specimen showing non-biomineralized structures.Its anterior, central and posterior parts are differently deformed.The middle part of the gladius is embedded in soft body that retains its cylindrical shape in the middle part of the specimen; the cephalic area is not preserved (Fig. 2A).The gladius is thin-walled, micro-laminated, flexible, diagenetically phos-phatized and apparently originally chitinous (SOM: table 1; Fig. 9C).It is ca.42.2 mm long, anteriorly tapered and exhibits a large conus at its posterior end (Figs.2, 3).The median field is narrow and anteriorly ended by a free rachis (Figs.2A, 3).The extremity of the rachis is broken and its actual length is unknown; the measured length is about 4 mm.The lateral fields are narrow, long, and acute anteriorly (Fig. 2A 1 ).The conus is ca.8.3 mm long, that is ca.0.25 of the gladius length (Fig. 2A, C 1 ).The posterior extremity of the conus approximately corresponds to the top of the V-shape "sinus" between fins (Fig. 2C).The conus shows a small lateral tooth-like structure (Fig. 2A 2 , B, C 1 ).The smooth outer surface of the gladius is exposed in its most anterior tapered part (Fig. 2A), in the conus (Fig. 2A 1 , C 1 ) and in a tiny ~3 mm apical part of the gladius that is displaced from its original position and seen in the marginal part of the conus (Fig. 2C).The apical gladius has slowly expanded narrow median and two lateral fields with broadly rounded anterior outline; the central field being slightly longer and broader that lateral ones.This highlights the presumed ontogenetic transformation of the rounded frontal outline of the juvenile gladius into the tapered frontal outline in later ontogenetic stages.It is worth noting that the ontogenetic stage that would be characterized by a Loligosepia-type gladius showing a broad triangular median field, is missing in the ontogeny of Idahoteuthis parisiana Doguzhaeva and Brayard gen.et sp.nov.In the middle part, the gladius is deformed in a way that its sides are brought together and overlap one another.Because the left half of the gladius is broken and removed, soft tissue remains are exposed there (Fig. 2A, B).This part of the specimen is occupied by a large, oval, phosphatized stomach (Fig. 2A 1 ).Due to compaction, the latter likely looks larger, than it was originally.
The stomach exhibits a lighter color than other structures in this area.It has a gently folded periphery along the ventral side but it is less deformed along the dorsal side (Fig. 2A).
The stomach contains irregularly dispersed deformed arm hooks, ten of which have been found on a fracture plan (Fig. 4).It is worth to note that the stomach of the Late Cretaceous "fossil squid" Dorateuthis contained the undigested fish remains (Lukeneder and Harzhauzer 2004).In addition to the arm hooks, the exposed surface of the stomach displays scattered tiny, black sheet fragments of potential flooded ink.Like the arm hooks, ink exhibits a micro-globular ultrastructure and a carbon composition (Fig. 9A; SOM: table 1).
Posteriorly, a pair of pear-like, fin-supported cartilages and fins complete the specimen (Figs.2A, C 1 , 5, 6, 8A).They adjoin the conus; both being approximately equally long.The mantle is exposed like a ventral band -shape structure extending from the conus along the ventral margin of the soft body (Fig. 2A 2 , B).It might provide postmortem fixation of the cylindrical shape of the body on the ventral side where other supporting structures were missing.The ventral mantle is also represented by a patch preserved in front of the conus; it has thin, wavy longitudinal ridges (Fig. 2B).On the dorsal side, the gladius is coated by a bandshape structure of thin cartilaginous mantle (Figs.ly-dispersed mantle debris are identified by their plastic micro-deformation and micro-granular ultrastructures typical for fossilized non-biomineralized materials (Fig. 9A, E, F; for comparison see Doguzhaeva et al. 2004b: figs. 2A, B;Doguzhaeva et al. 2007a: figs. 6.7A-E;Doguzhaeva et al. 2007b: figs. 11.3-11.7;Doguzhaeva et al. 2010b: figs. 2-9).
Stratigraphic and geographic range.-Typelocality and horizon only.

Discussion
Phylogenetic implications.-Naef (1922) suggested that the evolutionary development of the gladius started based on a broad Loligosepia-type gladius progressively narrowing, with a median field reducing up to a thin rib or rachis leading to the narrow gladii of extant taxa.In this way, Jeletzky (1966) considered the Suborder Loligosepiina Jeletzky, 1965 as the stem group of modern oegopsid and myopsid squids.Morphological similarities between the gladii of the Early Jurassic Loligosepia, characterized by a broad triangular median field (see Fuchs and Weis 2008;Donovan and Boletzky 2014), and extant squid Thysanoteuthis were also interpreted as evidence of an ancestor-descendant relationship between these two genera by Starobogatov (1983).These similarities were oppositely considered as having no phylogenetic value by Nesis (1992).Young et al. (1998) assumed that the gladius appeared at least four times in extant taxa Vampyromorpha, Oegopsida, Myopsida, and Sepiolidae.Vecchione et al. (1999) also suggested that a three-part gladius with a broad median field and wings has no value for determining phylogenetic relationships.Later, Kröger et al. (2011) endorsed this view. Fuchs et al. (2013) described a Loligosepia specimen showing eight, rather than ten, arms in an arm crown.Since this discovery, loligosepiids have been considered separately from modern Decabrachia (Fuchs et al. 2013) and Donovan and Boletzky (2014) suggested that Loligosepia lies near the origin of Recent Octobrachia during the Early Jurassic.Following this view, fossil gladii with a Loligosepia-type gladius fall in Octobrachia rather than Decabrachia.This might be the case for the Middle Triassic Reitnerteuthis and the Late Triassic Germanoteuthis in which the median field is breviconic and triangular (Schweigert and Fuchs 2012).Contrary to these two Middle and Late Triassic genera, the Early Triassic Idahoteuthis Doguzhaeva and Brayard gen.nov.may fall in Decabrachia because of its narrow median field.Narrow gladii are well documented in e.g., younger Plesioteuthis from the Late Jurassic (Donovan and Toll 1988;Fuchs et al. 2007Fuchs et al. , 2015;;Klug et al. 2010Klug et al. , 2015)).Based on morphological similarities with gladii of extant squids (Ommastrephidae) (i.e., a narrow and long rachis, median and lateral keels, and the conus), Plesioteuthis was considered as the rootstock of oegopsid squids (Jeletzky 1966;Donovan and Toll 1988).Based on recently recovered beaks Plesioteuthis was as-signed to Decabrachia (Klug et al. 2010), however based on two pairs of fins and cirrate arms, Plesioteuthis has been assigned to octobrachians (Klug et al. 2015).
A narrow gladius is also known in e.g., the Early Cretaceous Nesisoteuthis.Judging on a shape of growth lines, it has a pointed median field and is even more similar to ommastrephids than the Jurassic Plesioteuthis.However, whether Nesisoteuthis has a conus remains unknown as a single specimen of this genus is available and does not show a preserved posterior part (Doguzhaeva 2005: figs. 1A-C).
Idahoteuthis Doguzhaeva and Brayard gen.nov. is preceded by the Early Permian gladius-bearing coleoid Glo chinomorpha stifeli (Gordon 1971) that shows limited morphological similarity with the other known gladii (Doguzhaeva and Mapes 2015: figs. 1-3).Recently obtained data on Glochinomorpha via ultrastructural and chemical approaches, however, suggests that: (i) the gladius appeared in the late Paleozoic, rather than in the Middle-Late Triassic, (ii) its appearance preceded Middle-Late Triassic phragmoteuthids still having a phragmocone, (iii) the biochemical development of shell material (sensu secretion of non-biomineralized, apparently chitinous, shell material as opposed to aragonite in the phragmocone of Phragmoteuthis) preceded its morphological transformation (sensu typical gladius structure with a limited number of longitudinal sectors and the presence of a conus), and (iv) the combination of the archaic gladius morphology and advanced gladius composition results from the asynchronous appearance of biochemical and morphological innovations in early evolutionary stages of squids (Doguzhaeva and Mapes 2015).Thus, a high evolutionary rate corresponding to the assumed morphologic transformation of the Glochinomorpha-type gladius (see Doguzhaeva and Mapes 2015: figs.1A-H, 2-4) into a tapered, narrow Idahoteuthis-type gladius (Figs.2A) have taken place during the Early Permian-Early Triassic interval.The Early Triassic occurrence of the Idahoteuthis-type gladius supports a scenario where gladius-bearing coleoids evolved independently from the proostracum-bearing belemnoids, including phragmoteuthids (see Doguzhaeva 2012).Even if Phragmoteuthis-type proostraca are found in older intervals than the middle Olenekian (see Rosenkrantz 1946), a direct evolutionary transformation of this shell type into a gladius would request the unlikely short-time combination of the following processes: (i) the elimination of a phragmocone comprising about 20 camerae, septa, septal necks, connecting rings and conotheca; (ii) the elimination of a soft siphuncle, including blood vessels and connecting tissues, running through approximately 20 camerae of the phragmocone; (iii) the re-organization of the soft tissues and muscular system; (iv) the development of physiological processes that can have enhanced secretion of chitin and associated proteins, instead of aragonite shell material; and (v) the appearance of a new locomotion system.Keeping this in mind, a direct transformation of the Phragmoteuthis-type shell into an Idahoteuthis-type gladius is hardly conceivable in a relatively short geological time interval.For the same reasons, the Phragmoteuthis lineage can hardly be considered, in our opinion, as the rootstock of Decabrachia or Octobrachia (Fuchs and Iba 2015).
To sum up, the earliest known gladii are presently known due to the Early Permian Glochinomorpha and the Early Triassic Idahoteuthis.Contrary to Glochinomorpha-type gladius, the Idahoteuthis-type gladius exhibits advanced morphological characters: three narrow longitudinal fields and a conus that are developed in extant Myopsida and Oegopsida.Based on molecular data, the divergence time for Myopsida appears close to the Late Permian/Early Triassic interval (Strugnell et al. 2006).The divergence time for Decabrachia is older (Strugnell et al. 2006), which is in agreement with the Late Carboniferous occurrence of the spirulid Shimanskya (Doguzhaeva et al. 1999).
Implications for Early Triassic food webs.-Numerousarm hooks have been collected in coprolites from the same exposures where Idahoteuthis Doguzhaeva and Brayard gen.nov.was found.Thus, in the middle Olenekian of the western USA basin, some coleoids were a prey for indeterminate predators, likely large-sized vertebrates such as fishes or ichthyosaurs (Brayard et al. 2017).For instance, chondrichthyan remains corresponding to specimens of about 1 m in length are common in some coeval exposures from Idaho (Romano et al. 2013).Ichthyosaur remains are also known from neighboring localities, and can have also been potential hunters for coleoids (Brayard et al. 2017).A strong prey-predator trophic relationship between coleoids and vertebrates thus may have existed during the middle Olenekian, at least in the Western USA basin.Based on the chitinous, thin-walled, tapered narrow gladius indicative of a streamlined body, the well-developed fin cartilages, the posterior fins, and the arm-hooks in the stomach, I. parisiana Doguzhaeva and Brayard gen.et sp.nov.was probably well adapted for active swimming and may have also been a small size predator inhabiting the subequatorial shallow warm sea on the west coast of Pangaea.Overall, the presence of eroded and deformed arm-hooks in the stomach of Idahoteuthis (Fig. 4) suggests cannibalism among Early Triassic coleoids, as frequently encountered in extant squids (Ibánez and Keyl 2010).Such trophic links among coleoids and between coleoids and other taxa highlight the multi-layered marine trophic network in the subequatorial warm shallow water marine environment of the west coast of Pangaea soon after the end-Permian mass extinction.

Conclusions
An Olenekian (Early Triassic) small size squid Idahoteuthis parisiana Doguzhaeva and Brayard gen. et sp. nov. and Idahoteuthidae Doguzhaeva and Brayard fam. nov.are described on the basis of a narrow, tapered, thin-walled gladius embedded in cylindrical body showing a pair of fins, large fin-supported cartilages, a dorsal cartilaginous band-like mantle structure, ventral non-cartilaginous band-like mantle structure and a stomach containing undigested arm hooks and flat patches of ink.The family Idahoteuthidae assumedly belongs to order Myopsida.
Idahoteuthis parisiana evidences the fossil squids inhabited the subequatorial warm shallow sea on the west coast of Pangaea in the Early Triassic; they were mobile predators, but also a prey for larger predators, including coleoids.Cannibalism of I. parisiana is deduced from the stomach content comprising undigested arm hooks.The micro-laminated lifetime chitin material of the gladius, microenvironments linked to diverse microbial blooms, and transient anoxic/disoxic conditions are considered as the main potential factors leading to the formation of the multiple fossilization types of the gladius and soft tissue body remains.

Fig. 1 .
Fig. 1. A. Palaeogeographic map of the western USA basin during the Early Triassic.B. Present-day location of the studied exposure.C. Synthetic stratigraphical and lithological succession of the Bear Lake area (after Romano et al. 2013) with position of the studied specimen.Ammonoid zonation after Jenks et al. (2013) and Jattiot et al. (2016).Stratigraphy follows the main units defined by Kummel (1954).Radiometric ages after Galfetti et al. (2007) and Burgess et al. (2014).Abbreviations: LL, Lower Limestone; LS,Lower Shale; ML, Middle Limestone; MS, Middle Shale; UCS, Upper Calcareous Siltstone.

Fig. 2 .
Fig. 2. Coleoid cephalopod Idahoteuthis parisianaDoguzhaeva and Brayard gen.et sp.nov.(holotype, UBGD 30545); middle Olenekian, Early Triassic; Idaho, USA.UBGD 30545.A. Overall view of the specimen showing the anteriorly tapered gladius embedded in soft tissues and uncertain organic structure positioned at its tapered end.Photograph (A 1 ) and explanatory drawing (A 2 ).B. Conus (B 1 ) and its counterpart (B 2 ) showing the outer and inner surfaces, respectively, as well as adjacent part of soft body to show a band-like mantle structure bordering a body ventrally and continuing from the conus forward and a mantle coating the ventral side of the body and showing a mantle rippled pattern (see A 2 ).C. Posterior portion of the specimen showing position (C 1 ) and structute (C 2 ) of tiny fragment of the apical gladius showing three narrow slowly expended fields with rounded anterior outlines.Abbreviations: b, bite mark; co, conus; dcm, dorsal cartilaginous mantle; f, fin; fc, fin cartilage; g, gladius; lf, left lateral field; m, mantle; mb, mantle band-like structure; mf, median field; r, rachis; rf, right lateral field; s, stomach; sbr, soft body remains; std, soft tissue debris; uos, uncertain organic structure.

Fig. 4 .
Fig. 4. Coleoid cephalopod Idahoteuthis parisiana Doguzhaeva and Brayard gen.et sp.nov.(holotype, UBGD 30545); middle Olenekian, Early Triassic; Idaho, USA; arm-hooks in the stomach.A. A well exposed arm-hook with deformed shaft and a broken distal end of the basement, tip not exposed; another arm-hook less visible and fractured.B. Three deformed arm-hooks.C. A deformed arm-hook showing a depression along the compressed shaft.Abbreviations: h, arm-hook; i, ink sheet-like patch.