Introduction

In the Middle Jurassic, a belemnite fauna was essentially reorganised in the Boreal seas. From Siberian data, it follows that abundant and highly diverse Toarcian–Early Aalenian belemnite assemblages were transformed into quantitatively and taxonomically poor faunas in latest Aalenian–Bathonian times, with an especially dramatic diversity drop during the time interval from the beds with Normannites to the Boreiocephalites borealis Zone (e.g., Sachs and Nalnjaeva 1975; Shurygin et al. 2000; Meledina et al. 2005), i.e., during the mid-Early Bajocian (cf. Meledina 2014; de Lagausie and Dzyuba 2017). In the Bajocian, soon after the extinction of the Hastitidae, the Cylindroteuthididae appeared and began to replace the last representatives of Megateuthididae and Pseudodicoelitidae. This event is considered as the beginning of a new stage in the evolution of Boreal belemnites (Meledina et al. 2005). Up to the first half of the Bathonian, only Paramegateuthis (Megateuthididae) and probably Lenobelus (Pseudodicoelitidae) co-existed with cylindroteuthidids in the high-latitude Boreal seas (Sachs and Nalnjaeva 1975; Doyle and Kelly 1988; Meledina et al. 2005; Mitta et al. 2015; for age interpretation see de Lagausie and Dzyuba 2017). Since the end of the Bathonian, the Cylindroteuthididae were the only belemnites, developing in the Arctic basin during the Jurassic (e.g., Sachs and Nalnjaeva 1979; Doyle 1987; Dzyuba 2004; Meledina et al. 2005). In northern Siberia, Megateuthididae and Cylindroteuthididae co-occur in strata embracing the interval from the Cranocephalites gracilis ammonite Zone to the so-called ‘beds without ammonites’ located between the Arcticoceras ishmae and Arcticoceras cranocephaloide ammonite zones, i.e., in the interval from the uppermost Lower Bajocian to the lowermost Middle Bathonian (de Lagausie and Dzyuba 2017).

The first belemnite described from the Bajocian–Bathonian boundary deposits of northern Siberia is Cylindroteuthis spathi Sachs and Nalnjaeva, 1964 (Cylindroteuthididae). Subsequently, Sachs and Nalnjaeva (1966, 1975) described several belemnite taxa belonging to Cylindroteuthididae and Megateuthididae from the Yuryung-Tumus Peninsula, Anabar Bay, Anabar River, Olenyok River, and the Lena River Basin (see Appendix). The problematic Pseudodicoelites sp. (Pseudodicoelitidae), which may belong to Lenobelus, has been reported from Anabar Bay (Sachs and Nalnjaeva 1975).

One of the Boreal key sections for the Lower–Middle Jurassic interval is situated on the Yuryung-Tumus Peninsula, where an Upper Pliensbachian to Middle Bathonian succession is very well exposed (Meledina et al. 1987; de Lagausie and Dzyuba 2017). A recent study of a new collection of belemnites from the peninsula made it possible to (1) define the precise vertical ranges of several key belemnites in the Bajocian–Bathonian boundary interval, (2) establish interregionally correlatable belemnite zones, and, finally, (3) refine the biostratigraphy across the Bajocian–Bathonian boundary in northern Siberia (de Lagausie and Dzyuba 2017).

In this paper, we describe new belemnite species belonging to Megateuthididae and Cylindroteuthididae from the Bajocian–Bathonian boundary interval of the Yuryung-Tumus Peninsula. Furthermore, we provide a palaeontological description of the Yuryung-Tumus specimens of Paramegateuthis subishmensis Stoyanova-Vergilova, 1983, which is the index species of the Siberian P. subishmensis belemnite zone traceable to Bulgaria, and we illustrate this species in full. Previously, only a single Arctic (Siberian) specimen, assigned to P. subishmensis, has been illustrated in the literature (de Lagausie and Dzyuba 2017). The palaeobiogeographic implications of the new belemnite data are also considered here.

Geological setting

The studied outcrops are located on the Yuryung-Tumus Peninsula between Khatanga Gulf and Nordvik Bay, northern Siberia, Russia (Fig. 1). The uppermost Lower Bajocian to Middle Bathonian strata are generally well-exposed in a number of coastal cliffs along the eastern edge of the peninsula. The belemnite remains were collected from the upper two-thirds of the stratotype section of the Yuryung-Tumus Formation (outcrops 17“Z”, 17“I”, 19“G”, and 20“G” sensu Meledina et al. 1987), which predominantly consists of siltstone and claystone, and contains numerous subglobular calcareous concretions, pyrite nodules, and glendonite aggregates (Figs. 2, 3). The examined interval of the section (members XVII to XXI) is approximately 100.5 m thick. Belemnites (Paramegateuthis, Cylindroteuthis, and Pachyteuthis) are rare throughout the section. Ammonites, bivalves, foraminifers, ostracods, crinoids, and plant fossils have also been reported from the section (e.g., Meledina et al. 1987; Nikitenko et al. 2013).

Fig. 1
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Location of the studied outcrops on the Yuryung-Tumus Peninsula, northern Siberia

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Fig. 2
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Correlation of the studied outcrops at the Yuryung-Tumus Peninsula, modified after Meledina et al. (1987), and levels from which the belemnites were collected

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Fig. 3
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Biostratigraphy and distribution of belemnites throughout the Bajocian–Bathonian boundary deposits at the eastern edge of the Yuryung-Tumus Peninsula modified after de Lagausie and Dzyuba (2017), with the addition of records of new belemnite species (for legend see Fig. 2). The approximate position of previous records (Sachs and Nalnjaeva 1975; Nalnjaeva 1986; Meledina et al. 1987) is shown by the dotted line: not illustrated records are displayed in grey colour, and records that are not found in situ are indicated with asterisks

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The sedimentary environment is interpreted as a moderately shallow marine setting, from the middle sublittoral zone to the outer part of the upper sublittoral zone (Nikitenko et al. 2013). According to Smith et al. (1994) and Scotese (2014), this basin was located at the palaeolatitude of ~75°N in the Middle Jurassic.

The zonal scales based on ammonites, belemnites, bivalves, foraminifers, and ostracods follow the biostratigraphic scheme proposed by Nikitenko et al. (2013) and recently revised by us in the belemnite part and in the age interpretation of all faunal successions (de Lagausie and Dzyuba 2017).

Materials and methods

The belemnite specimens, CSGM2070/9–20, are stored in the Central Siberian Geological Museum (CSGM), Novosibirsk, Russia. All these specimens were collected in 2009 from the Yuryung-Tumus section. This collection continues the earlier illustrated collection, CSGM2070/1–8 (de Lagausie and Dzyuba 2017), which contained biostratigraphically important belemnites (CSGM2070/1–7) and ammonite (CSGM2070/8) from the Bajocian–Bathonian transition beds of the Yuryung-Tumus Peninsula. Belemnite collections CSGM83, 84, 87–89, 91 of Sachs and Nalnjaeva (Sachs and Nalnjaeva 1964, 1966, 1975; Efremova et al. 1983; Nalnjaeva 1986, 1989; Meledina et al. 1998; Repin et al. 2006; Nalnjaeva et al. 2011) were also studied for comparative analysis of new belemnite material.

Belemnite terminology mainly follows that of Doyle and Kelly (1988). The measurements (in mm) were as follows: L, total preserved length; l, length from apex to tip of alveolus; D v, dorso-ventral diameter at the tip of the alveolus; D l, lateral diameter at the tip of the alveolus. Additionally, following Sachs and Nalnjaeva (1964), we calculated the degree of rostrum elongation (l/D v, × 100%) and compression (D l/D v, × 100%). Approximate size (length) ranges are given by the terms small (<60 mm), medium (60–100 mm) and large (>100 mm). Rostra were coated with magnesium oxide prior to photography.

Systematic palaeontology

We use the classification system adopted by Dzyuba (2011) for Cylindroteuthididae and Dzyuba et al. (2015) for Megateuthididae. The main characters, distinguishing these belemnite families, include the number and position of rostrum grooves and the shape of juvenile rostrum. The Early–Middle Jurassic family Megateuthididae possesses more or less developed dorsolateral apical grooves, sometimes in combination with a ventral apical groove. The Middle Jurassic to Early Cretaceous family Cylindroteuthididae is characterised by a ventral apical groove. Juveniles of Megateuthididae are generally conical to cylindriconical, whereas juveniles of Cylindroteuthididae are cylindrical to slightly subhastate (spindle-like).

Subclass Coleoidea Bather, 1888

Order Belemnitida von Zittel, 1895

Suborder Belemnitina von Zittel, 1895

Family Megateuthididae Sachs and Nalnjaeva, 1967

(= Mesoteuthidae Gustomesov, 1977; = Acrocoelitidae Riegraf, 1980, nom. transl. Riegraf 1995)

Genus Paramegateuthis Gustomesov, 1960

1958 Paramegateuthis Gustomesov: p. 158, nom. nud.

Type species. Megateuthis (Paramegateuthis) ishmensis Gustomesov, 1960.

Other species included. P. manifesta Nalnjaeva in Sachs and Nalnjaeva, 1975, P. nescia Nalnjaeva in Sachs and Nalnjaeva, 1975, P. ovata de Lagausie and Dzyuba sp. nov., P. schurygini Dzyuba sp. nov., P. subishmensis Stoyanova-Vergilova, 1983, and P. zimevizensis Stoyanova-Vergilova, 1983 (composed the group with elongated rostrum, along with the type species); P. bella (Barskov in Mitta et al. 2004), P. gustomesovi Stoyanova-Vergilova, 1983, P. nalnyaevae Doyle in Doyle and Kelly, 1988, P. parabajosicus Nalnjaeva in Sachs and Nalnjaeva, 1975, P. parabella (Barskov in Mitta et al., 2004), P. pressa Nalnjaeva in Sachs and Nalnjaeva, 1975, P. timanensis (Gustomesov, 1960), and probably P. bajosicus (Ivanova, 1959) (composed the group with relatevly short rostrum).

Remarks. The genus is represented by the compressed, conical to cylindriconical, commonly small to medium sized species of Megateuthididae, with elongated dorsolateral apical grooves, a goniolineate apical line, and a nearly central alveolus with an acute alveolar angle. Paramegateuthis most closely resembles Megateuthis Bayle, 1878, but the latter differs in its larger and stouter rostrum with short dorsolateral apical grooves. Moreover, some Megateuthis develop an epirostrum.

Stratigraphic and geographic distribution. Middle Aalenian (Bradfordensis Chronozone) to Middle Bathonian of northern and eastern Europe, northern and northeastern Asia, and (?) northern North America.

Paramegateuthis ovata de Lagausie and Dzyuba sp. nov.

Figure 4a, b

Fig. 4
figure 4

Belemnites from the Lower Bajocian of the Yuryung-Tumus Peninsula (a–c) and Anabar Bay (d), northern Siberia. a, b Paramegateuthis ovata de Lagausie and Dzyuba sp. nov. a Specimen CSGM2070/9, the holotype: ventral (a 1 ), right lateral (a 2 ), dorsal (a 3 ) views, longitudinal section in view a 1 (a 4 ), and cross-sections near the anterior end (a 5 ) and in the apical region (a 6 ). b Specimen CSGM2070/10: ventral (b 1 ), left lateral (b 2 ), dorsal (b 3 ) views, and cross-section near the anterior end (b 4 ). c Paramegateuthis cf. subishmensis Stoyanova-Vergilova, 1983, specimen CSGM2070/11: ventral (c 1 ), right lateral (c 2 ), dorsal (c 3 ) views, longitudinal section in view c 1 (c 4 ) and cross-section near the tip of the alveolus (c 5 ). d Paramegateuthis subishmensis Stoyanova-Vergilova, 1983, specimen CSGM87-121, originally assigned by Sachs and Nalnjaeva (1975) to Paramegateuthis ishmensis (Gustomesov): ventral (d 1 ), right lateral (d 2 ) and dorsal (d 3 ) views

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1968 Mesoteuthis inornata (Phillips)—Moskalenko: p. 30, pl. 5, fig. 2.

1968 Mesoteuthis aff. rhenana (Oppel)—Moskalenko: p. 31, pl. 6, figs. 1–6.

1988 Paramegateuthis nescia Nal’nyaeva [Nalnjaeva]—Doyle and Kelly: p. 24, pl. 4, figs. 1–7.

Etymology. From ovata (Latin) meaning oval, egg-shaped, in reference to a shape of the rostrum cross-section.

Holotype. CSGM2070/9, a subcomplete rostrum (Fig. 4a).

Paratype. CSGM2070/10, a rostrum lacking the apex (Fig. 4b).

Locality and Horizon. Outcrop 17“Z”, bed 2, 150 cm below the top (CSGM2070/10), and near Outcrop 20“A”, the analogue of the base of bed 3 in Outcrop 17“Z” (the holotype), Yuryung-Tumus Peninsula, northern Siberia; Boreiocephalites borealis Zone, member XVII, Yuryung-Tumus Formation, Lower Bajocian, Middle Jurassic.

Diagnosis. Large-sized, moderately elongated, conical to cylindriconical rostrum. Cross-section strongly compressed, elliptical. Dorsolateral apical grooves elongated and shallow, but may be weakly incised. Alveolus occupying approximately one-third of the rostrum.

Description. Medium to large sized, moderately elongated rostrum (Table 1). The outline is symmetrical and conical to cylindriconical. The profile is nearly symmetrical and conical to cylindriconical. The lateral aspects are strongly flattened throughout the alveolar and stem regions. The apex is acute in outline and is slightly more obtuse in profile, and it is centrally located to slightly dorsally displaced. The cross-section is very compressed and elliptical, especially in the alveolar and stem regions. Dorsolateral apical grooves are developed as elongated and shallow to weakly incised depressions, and the apex may bear striae. Lateral lines are poorly defined. The alveolus is centrally located, slightly compressed and elliptical in the cross-section and occupies approximately one third of the rostrum. The alveolar angle is 22°. The earliest juvenile stages are elongated conical (Fig. 4a4).

Table 1 Measurements for Paramegateuthis ovata de Lagausie and Dzyuba sp. nov.
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Comparison. The species is very similar to P. nescia Nalnjaeva in size and in having the elongated and commonly shallow dorsolateral apical grooves, but is easily distinguished due to its well-developed lateral flattenings and strongly compressed cross-section (72–76 vs. 83–95% in P. nescia, according to Sachs and Nalnjaeva 1975). Moreover, unlike P. nescia, the new species is not slender, and its apex is more obtuse in profile. In the degree of rostrum compression, P. ovata sp. nov. is close to the two very compressed but extremely short species of Paramegateuthis, namely, P. parabajosicus Nalnjaeva and P. pressa Nalnjaeva. The new species differs from P. zimevizensis Stoyanova-Vergilova and P. subishmensis Stoyanova-Vergilova by its larger size, its more elongated and less conical shape, and its more shallow dorsolateral apical grooves.

Remarks. The large-sized Mesoteuthis inornata and medium-sized Mesoteuthis aff. rhenana, both described by Moskalenko (1968) from the basal beds of the Oshurkova Formation on the Urkan River (upper reaches of the Amur River, the Russian Far East), share similar characteristics with P. ovata sp. nov. The compression rate is equivalent for the Siberian specimens and “M. aff. rhenana”, but the latter specimens are slightly more elongated, in all probability due to their lower maturity stage. According to Dzyuba and Nalnjaeva (2011), the basal beds of the Oshurkova Formation most likely correspond to the uppermost Lower Bajocian. The mid-Toarcian–earliest Aalenian Megateuthis rhenana (Oppel), including Belemnites inornatus Phillips as a synonym sensu (Doyle 1992), is larger in size and less compressed, and generally has shorter dorsolateral apical grooves.

The non-slender and strongly compressed P. nescia, described by Doyle and Kelly (1988) from the upper part of the Passet Member (Middle Jurassic, below the first records of Arcticoceras) of Kongsøya and the lower part of the Dunnérfjellet Member (Lower Bathonian, beds with Arcticoceras cf. harlandi Rawson) of Svenskøya (Kong Karls Land, Svalbard), is assigned herein to the new species. Both the Svalbard material and the Russian Far East material illustrate the uniform variation of a rostrum shape, which ranges from conical to almost cylindrical.

Stratigraphic and geographic distribution. Lower Bajocian (Boreiocephalites borealis Zone) of northern Siberia (Yuryung-Tumus Peninsula), and the Russian Far East (Amur River Basin); Middle Jurassic (pre-Middle Bathonian strata, the general stratigraphic position in the strata is not specified) of Svalbard (Kong Karls Land).

Paramegateuthis schurygini Dzyuba sp. nov.

Figure 5f–h

Fig. 5
figure 5

Belemnites from the Lower Bajocian (a–e, i) and Lower–Middle Bathonian (f–h) of the Yuryung-Tumus Peninsula, northern Siberia. a–e Paramegateuthis subishmensis Stoyanova-Vergilova, 1983. a Specimen CSGM2070/12: ventral (a 1 ), right lateral (a 2 ) and dorsal (a 3 ) views. b, c Specimens CSGM2070/13, 14: cross section at the tip of the alveolus. d Specimen CSGM2070/15: ventral (d 1 ), left lateral (d 2 ) and dorsal (d 3 ) views. e Specimen CSGM2070/16: ventral (e 1 ), left lateral (e 2 ), dorsal (e 3 ) views, and cross-section near the anterior end (e 4 ). f–h Paramegateuthis schurygini Dzyuba sp. nov. f Specimen CSGM2070/18, the holotype: ventral (f 1 ), right lateral (f 2 ), dorsal (f 3 ) views, and cross-section near the anterior end (f 4 ). g Specimen CSGM2070/19: ventral (g 1 ), right lateral (g 2 ), dorsal (g 3 ) views, and cross-section near the anterior end (g 4 ). h Specimen CSGM2070/2: ventral view (h 1 ) and fragment of longitudinal section (h 2 ). i Cylindroteuthis gelida de Lagausie sp. nov., specimen CSGM2070/20, the holotype: ventral (i 1 ), right lateral (i 2 ) views, and cross-section in the alveolar region (i 3 )

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2017 Cylindroteuthis cf. confessa Nalnjaeva—de Lagausie and Dzyuba: pl. 1, figs. 9–11.

Etymology. In honour of Prof. Boris N. Shurygin (Бopиc H. Шypыгин), Russian geologist and palaeontologist, and an expert on the Arctic Jurassic.

Holotype. CSGM2070/18, a subcomplete rostrum (Fig. 5f).

Paratypes. CSGM2070/19, a subcomplete rostrum (Fig. 5g); CSGM2070/2, an incomplete rostrum partially showing the alveolar and stem regions (de Lagausie and Dzyuba 2017, pl. 1, Figs. 9–11; Fig. 5h).

Locality and Horizon. Outcrop 19“G”, bed 11, 100 cm above the bottom (the holotype), bed 12, 150 cm above the bottom (CSGM2070/19), and 230 cm below the top (CSGM2070/2), Yuryung-Tumus Peninsula, northern Siberia; uppermost Paramegateuthis ishmensis Zone, member XXI, Yuryung-Tumus Formation, Lower Bathonian to Middle Bathonian transition, Middle Jurassic.

Diagnosis. Large-sized, elongated, slender conical to cylindriconical rostrum. Cross-section compressed, elliptical to weakly pyriform with a broader dorsum than venter. Long tiny dorsolateral apical grooves. Apex striated. Alveolus occupying one fourth of the rostrum.

Description. Large-sized, elongated, slender rostrum (Table 2). The outline is symmetrical and conical to cylindriconical. The profile is asymmetrical and cylindriconical, with a more inflated venter than dorsum. The apex is very acute and nearly centrally located. The cross-section is compressed, elliptical to weakly pyriform (dorsum is broader than venter) in the alveolar region, and elliptical in the stem and apical regions. The dorsolateral apical grooves are elongated but tiny, and apical striae may be well-developed. Lateral lines are present as a broad almost central depression, visible mainly in an anterior half of the rostrum. The alveolus is centrally located to slightly dorsally displaced and subcircular in the cross-section, and it occupies one fourth of the rostrum. The alveolar angle is 25°–27°. The earliest juvenile stages are elongated cylindriconical (Fig. 5h).

Table 2 Measurements for Paramegateuthis schurygini Dzyuba sp. nov.
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Comparison. The species most closely resembles P. nescia Nalnjaeva but is distinguished by its more cylindriconical and elongated rostrum, the apex of which may bear numerous striae. This new species is the most elongated of Paramegateuthis (Fig. 6).

Fig. 6
figure 6

Scatter plot of length from rostrum apex to tip of alveolus (l) to dorso-ventral diameter at the tip of the alveolus (D v) for some species of Paramegateuthis. Data from literary sources (Moskalenko 1968; Sachs and Nalnjaeva 1975; Doyle and Kelly 1988) are also used. The logarithmic regression curves are shown by the dotted lines. R 2 coefficient of determination

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Remarks. A rostrum lacking the apical region can be easily confused with Cylindroteuthis confessa Nalnjaeva (Cylindroteuthididae). In such a case, ontogeny investigations are required to verify the taxon name. One incomplete rostrum, reported by us from the Yuryung-Tumus section as C. cf. confessa (de Lagausie and Dzyuba 2017), appears to have megateuthidid ontogeny (Fig. 5h).

Paramegateuthis subishmensis Stoyanova-Vergilova, 1983

Figures 4d, 5a–e

pars 1975 Paramegateuthis manifesta Nalnjaeva—Sachs and Nalnjaeva: p. 62, pl. 9, figs. 6, 7.

pars 1975 Paramegateuthis ishmensis Gustomesov—Sachs and Nalnjaeva: p. 64, text-fig. 24.

1983 Paramegateuthis subishmensis—Stoyanova-Vergilova: p. 254, pl. 1, fig. 4; pl. 2, figs. 1, 2.

1990 Paramegateuthis subishmensis Stoyanova-Vergilova—Stoyanova-Vergilova: pl. 2, fig. 1.

1993 Paramegateuthis subishmensis Stoyanova-Vergilova—Stoyanova-Vergilova: p. 69, pl. 34, figs. 1–3.

2017 Paramegateuthis subishmensis Stoyanova-Vergilova—de Lagausie and Dzyuba: pl. 1, figs. 15–17.

Holotype. HIMG J2 1274, Sofia, Bulgaria; the core-drilling R5 near the village of Dolni Lukovit, depth 2986.5 m, Bulgaria; Stephanoceras humphriesianum Zone, Lower Bajocian, Middle Jurassic. Designated by Stoyanova-Vergilova (1983, pl. 2, fig. 1).

Studied material. Two well-preserved rostra (CSGM2070/4, 12), three partially complete rostra (CSGM2070/13, 15, 16), and two incomplete rostra partially showing the alveolar and stem regions (CSGM2070/14, 17); all from the member XVII, with the exception of CSGM2070/4, found at the base of member XX, all from the Yuryung-Tumus Formation. CSGM2070/12: Outcrop 20“G”, bed 3; CSGM2070/13, 16, 17: Outcrop 17“Z”, bed 1; CSGM2070/14: Outcrop 19“G”, bed 2; CSGM2070/15: Outcrop 17“Z”, bed 1, 150 cm above the bottom; CSGM2070/4: Outcrop 20“G”, bed 10, near the bottom.

Description. Medium-sized, moderately elongated rostrum (Table 3). The outline is symmetrical and conical. The profile is symmetrical to slightly asymmetrical due to the slightly inflated venter, and conical. The apex is acute to very acute and attenuated. The cross-section is subcircular in the anterior part of the alveolar region but is compressed and elliptical to weakly pyriform near the tip of the alveolus, in the stem and apical regions. Dorsolateral apical grooves may be strongly incised, especially in the apical region; anteriorly, they can be transformed into depressions, visible up to the alveolar region. In general, lateral lines are poorly defined. Striae are commonly not observed at the apex and the ventral apical groove is absent, but one specimen (CSGM2070/12) bears clearly defined three ventral striae (Fig. 5a1). The alveolus is centrally located, subcircular to compressed elliptical in cross-section and occupies approximately two fifths of the rostrum. The alveolar angle is 23°–25°.

Table 3 Measurements for Paramegateuthis subishmensis Stoyanova-Vergilova
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Comparison. The species somewhat resembles P. nescia Nalnjaeva but is distinguished by a less elongated and more conical rostrum, with a less asymmetrical profile and possessing more developed dorsolateral apical grooves. P. subishmensis is close to P. manifesta Nalnjaeva in the acutely conical shape of its rostrum. However, it differs from the latter by its slightly less elongated form and by the dorsolateral apical grooves, which are not closely spaced and commonly shorter. P. subishmensis is similar to P. zimevizensis Stoyanova-Vergilova in general shape and in having the incised dorsolateral apical grooves, but is more elongated and possesses a more attenuated apex. P. subishmensis may be confused with P. ishmensis (Gustomesov), but the former species is greater in size, more conical, and its apex tends to be attenuated.

Remarks. A single specimen, CSGM2070/4, recorded from the base of the Upper Bajocian at the Yuryung-Tumus section, was illustrated by us earlier (de Lagausie and Dzyuba 2017, pl. 1, figs. 15–17). Here, we illustrate several specimens from the Early Bajocian Boreiocephalites borealis Zone.

The representatives of P. manifesta recorded by Sachs and Nalnjaeva (1975) from the Boreiocephalites “pseudoborealis” (=borealis) Zone of Siberia, in our opinion, can be classified as P. subishmensis. At least two illustrated specimens, CSGM87-150 and 151, collected on the Yuryung-Tumus Peninsula (Sachs and Nalnjaeva 1975, pl. 9, figs. 6, 7), are closer to juveniles of the considered species due to the degree of elongation of their rostrum and the development characteristics of the dorsolateral apical grooves, which are less closely spaced than those of true P. manifesta Nalnjaeva. Moreover, P. ishmensis, described by Sachs and Nalnjaeva (1975), may partly be assigned to P. subishmensis; for example, the specimen CSGM87-121 (see Fig. 4d of present paper) is characterised by conical shape with an attenuated apex. According to the museum label, this specimen is from the “Lower Bathonian” (=Lower Bajocian; cf. de Lagausie and Dzyuba 2017) of Anabar Bay.

Stratigraphic and geographic distribution. Lower Bajocian (Stephanoceras humphriesianum Zone) of Bulgaria. In northern Siberia, the uppermost Lower Bajocian up to the Lower–Upper Bajocian boundary (Boreiocephalites borealis Zone to the base of the Arctocephalites arcticus Zone) of the Yuryung-Tumus Peninsula and Anabar Bay.

Paramegateuthis cf. subishmensis Stoyanova-Vergilova, 1983

Figure 4c

Studied material. CSGM2070/11, a rostrum partially lacking the alveolar and apical regions from Outcrop 17“I”, at the top of the outcrop; member XVII, Yuryung-Tumus Formation.

Description. Medium-sized, moderately elongated rostrum. The outline is symmetrical and conical. The profile is nearly symmetrical and cylindriconical. The apical region shows a tendency to be attenuated. The cross-section is compressed and elliptical (Table 4). The dorsolateral apical grooves are well-developed and strongly incised in the apical region. Lateral lines are not defined. The tip of the alveolus is centrally located.

Table 4 Measurements for Paramegateuthis cf. subishmensis Stoyanova-Vergilova
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Remarks. The specimen is closest to P. subishmensis Stoyanova-Vergilova in general shape, development characteristics of the dorsolateral apical grooves, and in tendency of the apical region to be attenuated. However, the incomplete preservation of the rostrum does not allow us to assign this specimen to P. subishmensis with certainty.

Stratigraphic and geographic distribution. Lower Bajocian (Boreiocephalites borealis Zone) of northern Siberia (Yuryung-Tumus Peninsula).

Family Cylindroteuthididae Stolley, 1919

(= Pachyteuthidae Stolley, 1919)

Subfamily Cylindroteuthidinae Stolley, 1919

Genus Cylindroteuthis Bayle, 1878

Type species. Belemnites puzosianus d’Orbigny, 1842.

Other species included. C. confessa Nalnjaeva in Sachs and Nalnjaeva 1975, C. gelida de Lagausie sp. nov., C. spathi Sachs and Nalnjaeva 1964, and numerous Callovian to Early Valanginian species.

Remarks. The genus contains the compressed, elongated cylindrical to cylindriconical, large-sized species of Cylindroteuthididae, with a generally inflated venter, a more or less developed ventral apical groove, a weakly cyrtolineate apical line, and a slightly excentric alveolus with an acute to very acute alveolar angle. Cylindroteuthis is easily distinguished from the related genus Arctoteuthis, Sachs and Nalnjaeva 1964 (Cylindroteuthidinae) which possesses a more flattened venter and uncompressed cross-section. Cylindroteuthis resembles Pachyteuthis Bayle, 1878 (Pachyteuthidinae) in its similar compression and inflated venter, but the latter is robust and has a more excentric alveolus and a strongly cyrtolineate apical line.

Stratigraphic and geographic distribution. Uppermost Lower Bajocian to Lower Valanginian of northern, western and eastern Europe, northern and northeastern Asia, and North America.

Cylindroteuthis gelida de Lagausie sp. nov.

Figure 5i

Etymology. From gelida (Latin) meaning frozen, in reference to a cold climate in the Arctic.

Holotype. CSGM2070/20, a well-preserved rostrum (Fig. 5i).

Locality and Horizon. Outcrop 19“G”, bed 5, near the top, just under the calcareous bed, Yuryung-Tumus Peninsula, northern Siberia; Cranocephalites gracilis Zone, member XVIII, Yuryung-Tumus Formation, Lower Bajocian, Middle Jurassic.

Diagnosis. Large-sized, moderately elongated, cylindriconical to subcylindrical rostrum. Cross-section rounded subquadrate. Ventral apical groove short but well-developed. Alveolus occupying two fifths of the rostrum.

Description. Large-sized, moderately elongated rostrum (Table 5). The outline is symmetrical and cylindriconical to subcylindrical. The profile is symmetrical and cylindriconical to subcylindrical. The apex is centrally located, moderately acute and devoid of striae. The cross-section is rounded subquadrate. The ventral apical groove is well-developed, deeply incised in the apical region, and then expanded and flattened in the posterior part of the stem region. Lateral lines are poorly defined. The alveolus is ventrally displaced, circular in cross-section and occupies two fifths of the rostrum.

Table 5 Measurements for Cylindroteuthis gelida de Lagausie sp. nov.
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Comparison. The morphologically closest species is C. spathi Sachs and Nalnjaeva, but the new species differs by its larger and notably less elongated rostrum (Fig. 7). Additionally, the alveolus of the new species is more displaced towards the venter.

Fig. 7
figure 7

Scatter plot of length from rostrum apex to tip of alveolus (l) to dorso-ventral diameter at the tip of the alveolus (D v) for some species of Cylindroteuthis. Data from literary sources (Sachs and Nalnjaeva 1964, 1975) are also used. The logarithmic regression curves are shown by the dotted lines. R 2 coefficient of determination

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Remarks. Both C. gelida sp. nov. and C. spathi are the earliest known species among Cylindroteuthis, which is believed to have appeared soon after the appearance of the first Pachyteuthis (e.g., Dzyuba and Nalnjaeva 2011). It should be noted that in the rostrum morphology the genus Pachyteuthis shows more similarity with the new species than with C. spathi. C. gelida sp. nov., representing moderately elongated species of the genus Cylindroteuthis, like Pachyteuthis is characterised by a rather excentric alveolus.

An incomplete rostrum, reported as Cylindroteuthis (Cylindroteuthis) sp. (Doyle and Kelly 1988, pl. 4, figs. 15–17) from Kong Karls Land (Svalbard), is closest to C. gelida sp. nov., but its species affiliation requires further investigation.

Palaeobiogeographic implications

Boreal and Tethyan belemnite realms can be recognised in the Bajocian and Bathonian (e.g., Sachs and Nalnjaeva 1975; Doyle 1987; Challinor et al. 1992). According to Challinor et al. (1992), the Arctic and Boreal-Pacific provinces are defined within the Boreal Realm for this time interval, whereas the Tethyan Realm can be subdivided into the Mediterranean, Himalayan and South Pacific provinces. New records from the Yuryung-Tumus section contribute to the belemnite palaeontological characteristics of the Arctic province (Fig. 8). In the mid-Middle Jurassic, Megateuthididae was represented in this province by the only genus Paramegateuthis, whereas Cylindroteuthididae was represented by Cylindroteuthis, Microbelus and Pachyteuthis.

Fig. 8
figure 8

Stratigraphic ranges of belemnites at the Bajocian–Bathonian boundary in the Arctic province compiled from numerous sources (see Appendix). Age interpretation is after de Lagausie and Dzyuba (2017), with application of information on East Greenland (Callomon et al. 2015), Svalbard (Dallmann 1999), Franz Josef Land (Dibner 1998), Pechora Basin (Mitta et al. 2015), and northern Siberia (Shurygin et al. 2000; Nikitenko et al. 2013). The solid line refers to the indubitable records; the dotted line shows records that require verification with respect to the age interpretation (black colour) or taxonomic affinity (grey colour)

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The earliest records of the genus Paramegateuthis are known from the Aalenian–Bajocian transition interval of Bulgaria (Stoyanova-Vergilova 1983, 1990), Dagestan in Northern Caucasus (Ippolitov et al. 2015), and tentatively also Svalbard (Doyle and Kelly 1988). The first appearance of Paramegateuthis in Siberia was recorded from the Bajocian beds lacking ammonites and referred to as “beds without ammonites” (Sachs and Nalnjaeva 1975) or Retroceramus clinatus bivalve Zone (Meledina et al. 1987). These beds are now assigned to the Chondroceras marshalli ammonite beds (cf. Shurygin et al. 2011) corresponding to the basal part of the Humphriesianum Chronozone (cf. Meledina 2014). However, Nalnjaeva (1986) also supposed the presence of Paramegateuthis in the preceding Retroceramus lucifer bivalve Zone, which embraces the upper part of the Arkelloceras tozeri ammonite Zone (cf. Shurygin et al. 2011); the locality remains unknown.

During the latest Early Bajocian to Middle Bathonian, Paramegateuthis became a typical faunal component of the Arctic province, but there are some records outside the Arctic, namely, Paramegateuthis subishmensis Stoyanova-Vergilova in Bulgaria (e.g., Stoyanova-Vergilova 1983), “Paramegateuthis” bajosicus (Ivanova), Paramegateuthis bella (Barskov) and Paramegateuthis parabella (Barskov) near Saratov in Central Russia (Ivanova 1959; Dzyuba in Mitta et al. 2014b), and Paramegateuthis “timanensis” (Gustomesov) in the south of the Russian Far East (Nalnjaeva in Challinor et al. 1992). It is noteworthy that Megateuthis (=Mesoteuthis, fide Doyle 1992), from the predominant genus among Megateuthididae during the early Middle Jurassic, was present essentially in the Mediterranean province of the Tethyan Realm (Doyle 1987; Doyle and Bennett 1995) but is also known from the Russian Far East (Kinasov in Efimova et al. 1968; Moskalenko 1968; Dzyuba and Nalnjaeva 2011), i.e., from the Boreal-Pacific province of the Boreal Realm (Fig. 9). Elsewhere, this genus completely disappeared to the end of the Bajocian (e.g., Doyle and Bennett 1995; Weis and Mariotti 2008; Dzyuba and Weis 2015).

Fig. 9
figure 9

Accepted biostratigraphic correlation of the Tethyan and Boreal ammonite schemes in the studied interval (a) and global distribution of the mid-Middle Jurassic belemnites recognised in the Boreal Realm (b). Compiled from numerous sources (see text and Fig. 8). Palaeogeography (170 Ma) is modified after R. Blakey (http://jan.ucc.nau.edu/rcb7/mollglobe.html; https://deeptimemaps.com); the position of the North Pole is marked by white cross

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The genera Cylindroteuthis, Microbelus and Pachyteuthis show a similar distribution pattern within the Arctic province in the Bajocian–Bathonian transition time (Fig. 9). Additionally, Pachyteuthis bodylevskii Sachs and Nalnjaeva and Pachyteuthis optima Sachs and Nalnjaeva were recorded from the Lower Bathonian of the Saratov vicinity, Central Russia (e.g., Mitta et al. 2014b), and few rostra externally not distinguishable from Cylindroteuthis and Pachyteuthis (the ontogeny of the rostra remained unknown) were found together in the pre-Callovian deposits of Central Ukraine (Nikitin 1977). At the beginning of the Callovian, i.e., an interval of global sea-level rise (Hallam 2001; Ruban 2015), cylindroteuthidids became widespread in northwestern and eastern Europe as well as on the north-western margin of North America, and at the end of the Bathonian or in the Callovian Cylindroteuthis also penetrated the northwestern Pacific up to the Tetori Basin, Central Japan (see Fig. 3 of Sano et al. 2010). The Early Bajocian genus Eocylindroteuthis, commonly considered as ‘early cylindroteuthidids’ of Europe, is currently assigned to Megateuthididae (Dzyuba et al. 2015).

The Bajocian–Bathonian megateuthidid and cylindroteuthidid taxa, reported from the northeastern Pacific region (southern Alaska, western Canada) and Arctic Canada (for summarised data see Stevens 1965: 160; Doyle and Kelly 1988: 40–44; Dzyuba 2004: 47, 56, 62–63), are still poorly investigated and need to be revised, and we did not include these data in this work. The concept considering the northeastern Pacific as a possible centre of origin of cylindroteuthidids in the mid-Bajocian time (Sachs and Nalnjaeva 1975; for a discussion see also Dzyuba and Nalnjaeva 2011) still requires confirmation by new reliable data.

The biogeographic distribution of Paramegateuthis, Cylindroteuthis and Pachyteuthis raises the question of the north–south (or south–north) migration pathways of these genera during the Bajocian–Bathonian. The first hypothesis is a migration by the Norway–Greenland pass (Viking Corridor, cf. Westermann 1993). However, palaeontological, tectonic, O and Nd isotope evidence suggest considerable restrictions of this seaway in Aalenian–Bathonian times (e.g., Meledina et al. 2005; Shurygin 2005; Dera et al. 2015; Korte et al. 2015). Moreover, all these belemnite genera were evidently absent in the Tethyan basins of Western Europe during the Bajocian–Bathonian (e.g., Doyle 1987). Since Paramegateuthis subishmensis Stoyanova-Vergilova was found only in the uppermost Lower Bajocian of Bulgaria (Stoyanova-Vergilova 1983, 1990) and northern Siberia (de Lagausie and Dzyuba 2017; present paper), supposed Cylindroteuthis and Pachyteuthis were recorded in Central Ukraine (Nikitin 1977) in the “Bathonian” beds, which also contain Holcobelus (an Aalenian–Early Bajocian belemnite genus sensu Weis et al. 2012), and the genera Paramegateuthis and Pachyteuthis were found together with Tethyan ammonites in the Lower Bathonian of the Middle Volga region in Central Russia (Mitta et al. 2014b); thus, we can imagine the presence of a passageway (or temporary passageways) between the Boreal and Tethyan seas in the European part of Russia during the Bajocian–Bathonian transition (Fig. 9). Recently, the earliest existence of an East European passageway in the Jurassic was argued for the end of the Late Bajocian on the basis of the co-occurrence of Tethyan ammonites and Boreal foraminifers in Central Russia (Mitta et al. 2014b). Herein, we conclude that a passageway could have been temporarily opened in the Early Bajocian Humphriesianum Chronozone.

As follows from the above, the genus Megateuthis was not present in the Arctic province but can be recognised in the Boreal-Pacific province of the Boreal Realm. The main hypothesis that we can make about the migration of Megateuthis from a dispersal centre in the Tethys is via pathways marginal to Asian terranes. Unfortunately, information about belemnites from Southeast and East Asia is scant and must be improved to confirm this hypothesis.

Another possible explanation of the appearance of Megateuthis in the northwestern Pacific is that Paramegateuthis represents just a dwarf form of Megateuthis, being developed mainly in the Arctic. It is noteworthy that Paramegateuthis nalnyaevae Doyle, Paramegateuthis nescia Nalnjaeva, Paramegateuthis ovata de Lagausie and Dzyuba sp. nov., and Paramegateuthis schurygini Dzyuba sp. nov. represent atypically large forms of Paramegateuthis, close in length to the smallest Megateuthis (e.g., Megateuthis beneckei Schwegler, the species without epirostrum), however, all of these species are characterised by long dorsolateral apical grooves typical of the Paramegateuthis. The latest Early Bajocian species “Mesoteuthis” soloniensis Nalnjaeva and Dzyuba known from the Russian Far East is very large and elongated, but simultaneously has very elongated dorsolateral apical grooves and apparently lacks an epirostrum (Dzyuba and Nalnjaeva 2011: p. 261, figs. 2a, b, c). In the Russian Far East, Megateuthis sp. indet., “Mesoteuthis inornata (Phillips)”, and “Mesoteuthis aff. rhenana (Oppel)” were also recorded by Moskalenko (1968) from the beds, which are currently considered as the latest Early Bajocian in age (Dzyuba and Nalnjaeva 2011). All specimens of “M. aff. rhenana” were referred by Sachs and Nalnjaeva (1975) to Paramegateuthis ishmensis (Gustomesov). In our opinion, these specimens and “M. inornata” actually belong to Paramegateuthis but are more similar to P. ovata sp. nov. However, Megateuthis sp. indet. (Moskalenko 1968: p. 29, pl. 5, fig. 4) as well as Megateuthis “elliptica” (Miller) from the Bajocian of the Artyk River in the Russian Far East (Kinasov in Efimova et al. 1968: p. 133, pl. 81, fig. 1) are closer to typical Megateuthis. Sachs and Nalnjaeva (1975) identified Far East M. “elliptica” with P. nescia; however, this identification seems unlikely considering the smaller rostrum of P. nescia and its longer dorsolateral apical grooves.

Krimholz (1947), Tuchkov (1954), Voronets (1962), Kinasov (in Efimova et al. 1968), and Sachs and Nalnjaeva (1975) reported numerous “Mesoteuthis” taxa from the Toarcian and Aalenian of northern Siberia and northeastern Russia. Several of these taxa were recently assigned to Rarobelus gigantoides (Pavlow) (Dzyuba et al. 2015); many others are similar to Acrocoelites and Odontobelus and evidently need to be revised (Dzyuba and Weis 2015). Therefore, it cannot be excluded that Megateuthis may have penetrated the Boreal-Pacific province for the first time at the end of the Early Bajocian. Considering the size of the rostrum and degree of elongation of the dorsolateral apical grooves as a product of intrageneric variability, the appearance of Megateuthis (?=Paramegateuthis) in the northwestern Pacific can be explained by a migration from the Arctic. However, this issue apparently requires further investigation.

Conclusions

The study of new material collected from the Bajocian–Bathonian transition beds of the Yuryung-Tumus Peninsula (northern Siberia) has revealed three new belemnite species: Paramegateuthis ovata de Lagausie and Dzyuba sp. nov., Paramegateuthis schurygini Dzyuba sp. nov. (Megateuthididae), and Cylindroteuthis gelida de Lagausie sp. nov. (Cylindroteuthididae). Siberian representatives of the species Paramegateuthis subishmensis Stoyanova-Vergilova, 1983, known from Bulgaria, are also described herein in detail. Additionally, P. cf. subishmensis is recorded very close to the base of the Lower Bajocian Boreiocephalites borealis ammonite Zone. These new findings provide evidence for a more diverse species composition of the mid-Middle Jurassic belemnite assemblages in the Arctic province than previously thought. P. ovata sp. nov. can also be considered as a faunal component of the Boreal-Pacific province in the latest Early Bajocian due to the “Mesoteuthis inornata” and “Mesoteuthis aff. rhenana” records (Moskalenko 1968) assigned here to this new species.

There are still many questions concerning the cause and timing of the appearance of some Middle Jurassic belemnites in different parts of the Boreal Realm. However, to explain the migration path of Paramegateuthis subishmensis, it seems reasonable to conclude that a passage in the European part of Russia between the Boreal and Tethyan seas was opened (at least, temporarily) in the Early Bajocian Humphriesianum Chronozone.