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Home , Bredyia, Dumortieria, Hammatoceratidae, Hildoceratoidea

PalZ https://doi.org/10.1007/s12542-018-0416-6

RESEARCH PAPER

First fnd of aptychi of Leioceras and (, ) in the of Northern Caucasus, Russia

Vasily V. Mitta1,2 · Günter Schweigert3 · Mikhail P. Sherstyukov4 · Volker Dietze5

Received: 17 January 2018 / Accepted: 4 May 2018 © Paläontologische Gesellschaft 2018

Abstract Aptychi are reported from the Lower Aalenian Leioceras opalinum Zone and Subzone of the Khussa-Kardonik section in Karachay-Cherkessia (Kuban River Basin). They are associated with conchs of the ammonites genera Leioceras and Bredyia (superfamily Hildoceratoidea) and interpreted as their lower jaws. The Hildoceratoidea aptychi are referred to a form group defned by Trauth as ‘cornaptychi’. Wide valves with a straight apical angle (morph I) probably belong to Bredyia. Aptychi with an acute apical angle (wide in the basal part; morph II) and relatively narrow ones (morph III) belong to macroconchs and microconchs of Leioceras, respectively. Aptychi assignable to Leioceras opalinum are herein also reported from South- ern .

Keywords Aalenian · Ammonites · jaws · Aptychi · Cornaptychi · Leioceras · Bredyia · Northern Caucasus · Southern Germany

Introduction found in situ within the body chambers of ammonite conchs whose taxonomic relationships are known (see Tanabe et al. Aptychi are bivalved shell-like organismic remains consist- 2015 for a recent review). Meek and Hayden (1864) frst ing of an inner dark horny lamella and outer symmetrically described the co-occurrence of an aptychus and a jaw-like paired calcite plates which are known from and Cre- appendage in the body chamber of the Late sca- taceous marine strata (Arkell 1957). Together with simple phitid Hoploscaphites nebrascensis and explained them as arched structures consisting only of horny substance, known the lower and upper jaws. Subsequent workers (e.g. Trauth as anaptychi, aptychi mostly occur individually but are rarely 1927, 1928, 1930, 1931, 1934, 1935, 1936, 1938; Schinde- wolf 1958) interpreted the aptychi and anaptychi as ammo- noid opercula, because their general outlines more or less Handling Editor: Christian Klug. ft with the corresponding ammonite apertures and are also * Günter Schweigert similar to the hood of modern Nautilus and opercula of some guenter.schweigert@smns‑bw.de gastropods. Meek and Hayden’s (1864) view was later justi- Vasily V. Mitta fed by Closs (1967) and Lehmann (1967, 1971, 1972, 1976) [email protected] who reported the anaptychus or aptychus–upper jaw–radula Mikhail P. Sherstyukov association within the body chambers of Late Palaeozoic [email protected] and Jurassic ammonoids. As a result of these and subsequent works, anaptychi and aptychi are now conclusively regarded 1 Borissiak Paleontological Institute of the Russian Academy of Sciences, Profsoyuznaya 123, Moscow 117647, Russia anatomically as ammonoid lower jaws (Nixon 1996; Tanabe et al. 2015), although they might have had multiple functions 2 Cherepovets State University, Lunacharskogo 5, Cherepovets 162600, Russia (Parent et al. 2014; Parent and Westermann 2016). Cornaptychus is one of the form genera of aptychi classi- 3 Staatliches Museum für Naturkunde, Rosenstein 1, 70191 Stuttgart, Germany fed by Trauth (1927, 1930, 1935, 1936) and is characterized by a shiny black surface with coarse folds. They are known 4 North Caucasus Federal University, Institute of Oil and Gas, Kulakova 16/1, Stavropol 355029, Russia to occur from the Lower to the (Arkell 1957). In situ fnds of cornaptychi within ammonite conchs 5 Nördlingen, Germany

Vol.:(0123456789)1 3 V. V. Mitta et al. belonging to genera of the Hildoceratoidea are long known was visited several times by two of the co-authors of this from the early Posidonia Shale of Southern Ger- paper (MS and VM). many (Quenstedt 1885, 1856), but occur in strata of this age The lower part of the section (upper Toarcian–Aalenian) as well in Great Britain (Lomax and Hyde 2012). is included in the upper part of the Dzhigiat Formation In late 2017, one of the authors (MS) found two concre- (established in Besnosov et al. 1960) and is represented tions with ammonites and their aptychi in the Lower Aal- mainly by gray and yellowish-brown sandstones, massive, enian in the Kuban River Basin. These aptychi, described with sideritic concretions, sometimes totally flled with below, are the frst fnds of ammonite jaws in the Aalenian ammonite shells and bivalves, and rare belemnite rostra. of Russia. Higher up in the section, the sandstones become more argillaceous, and at the top, they are replaced by arena- ceous claystones. The measured thickness of the Dzhigiat Locality and age Formation here is at least 25 m. It is overlain by at least 30-m-thick Lower Bajocian strata of dark gray argillite- The Jurassic section exposed in a gully on the left bank of like claystone with sideritic concretions assigned to the the Khussa Kardonikskaya River (tributary to the Bolshoi lower member of the Djangura Formation (established in Zelenchuk River) in the Khussa Kardonikskaya Village, Besnosov 1967). The basal part of this claystone is marked Zelenchuk District of Karachay-Cherkessia (Fig. 1) has by a bed of gray brecciated and clastic limestone up to been known for a long time and has been studied by many 1 m thick, widely occurring in the Kuban and Urup rivers’ geologists and palaeontologists. The exposed strata belong interfuve and known by geologists as the ‘crinoid horizon’ to the upper part of the Lower Jurassic up to the lower or ‘Bizhgon Beds’ (Besnosov 1967). part of the Upper Jurassic. In recent years, this section

Fig. 1 Map of the locality Khussa-Kardonik (Zelenchuk District, Karachai-Cherkesia, Russia)

1 3 First fnd of aptychi of Leioceras and Bredyia (Ammonoidea; Aalenian, Russia)

The aptychi come from two sideritic concretions flled with the term ‘beds with ammonites’ (Kazakova 1984: p. 4). with ammonites and found in a stratigraphic level 2 m above According to Kazakova, the beds with assemblage II corre- the base of the section observed in this area (Fig. 2). The spond to the Leioceras opalinum–Leioceras comptum zones ammonites, mainly small calcitic conchs (maximum diame- of the Northern Caucasus scale (Kazakova 1984). ter = 20–35 mm) with fne ornamentation, include Leioceras Kazakova (1978, 1984) correlated this zone with the mid- opalinum (Reinecke), L. costosum (Quenstedt) and the con- dle and upper part of the Opalinum Zone of the standard siderably less common and incompletely preserved Bredyia scale. She presumed a gap above the Upper Toarcian Pley- spp. and Pleurolytoceras cf. dilucidum (Oppel). A single dellia aalensis Zone up to beds IIa (or beds with no ammo- specimen of Pleydellia sp. found a few years earlier ex situ nites, which is not entirely clear from Kazakova’s publica- probably comes from this or a similar level. tions) corresponding to the Pseudolioceras beyrichi Subzone Upper Toarcian–Lower Aalenian ammonites of the of Germany (Westermann 1967), the Leioceras subglabrum Northern Caucasus have been extensively studied (e.g. Neu- and Leioceras opaliniforme subzones of (Contini mayr and Uhlig 1892; Renz 1904, 1914; Krimholz 1961). 1969, 1970) and most of the Leioceras opaliniforme Sub- Additionally, material from the Khussa-Kardonik section zone of England (Buckman 1898 in Buckman 1987–1907). has also been studied in detail by Migacheva (1962) and Unfortunately, Kazakova did not describe any sections. Kazakova (1984). Based on the study of the Khussa-Kar- However, judging from a lithological log of the Khussa-Kar- donik section, Kazakova (1984) proposed the most detailed donik section (Kazakova 1984: text and Fig. 1), the aptychi- subdivision of the Toarcian–Aalenian boundary interval bearing horizons could correspond to both bed IIa and bed in that area. In the basal Aalenian, immediately above the IIb. She indicated Pleydellia, Leioceras and upper Toarcian pseudoradiosa–Pleydellia spp. in bed IIa [H. subinsigne (Oppel) is currently assigned to Zone [assemblage I, according to Kazakova 1984], she rec- the genus Bredyia: Senior 1977]. There are no occurrences ognized three units termed ‘beds with ammonites’ (from of Pleydellia in bed IIb, but Tmetoceras and Catulloceras bottom to top): beds with Leioceras opalinum–Pleydellia are indicated along with Leioceras. Kazakova’s data on the aalensis [IIa]; beds with fnely ribbed Leioceras comptum distribution of ammonites in the Khussa-Kardonik section (L. opalinum–L. comptum) [IIb], and beds with coarsely are in many ways contradictory and are possibly based on ribbed Leioceras comptum (L. spathi–L. comptum) [IIc]. erroneous identifcations. In particular, one of the index Kazakova actually interpreted her ‘beds with ammonites’ species (Leioceras comptum) is not indicated for bed IIb as biostratigraphic units presently considered as faunal hori- (Opalinum–Comptum) in the Khussa-Kardonik section. zons (Callomon 1985). Prior to that, Kazakova (1978: p. 45) According to modern data, Cotteswoldia aalensis (Zieten), proposed the term ‘faunal level’, which she later substituted as well as Catulloceras, are restricted to the Toarcian (Elmi

Fig. 2 Part of locality Khussa-Kardonik; the arrows indicate a level of concretions with aptychi

1 3 V. V. Mitta et al. et al. 1997), whereas Leioceras uncum (Buckman) occurs an almost right apical angle (morphotype I); (2) almost as only in the Comptum Subzone of the Aalenian Opalinum wide, but with an acute apical angle (morphotype II); and Zone (Chandler and Callomon 2009). Accordingly, Kaza- (3) long, relatively narrow valve with an acute apical angle kova’s data need to be revised. Taking into consideration (morphotype III). The aptychi are small, on average about the presence of numerous Leioceras and rare Bredyia spp., 10 mm in length, contained in hard sideritic rock with brittle including B. cf. subinsignis (Oppel), we accept the age of the calcitic fossils, which complicates their further preparation. concretions with aptychi as corresponding to the Opalinum To describe the aptychi, we used the well-established ter- Chronozone and Subchronosubzone. More precise dating of minology and measurements (e.g. Trauth 1930; Arkell 1957; the level with aptychi in the Aalenian stratigraphic scheme Keupp and Mitta 2013). The ratio of the width (w) of the will require a detailed re-examination of ammonites of the aptychus-to-the length of the inner (symphysis) margin (l) Khussa-Kardonik outcrop. to compare with approximately—not exactly—correspond- ing parameters of the apertural part of the shell was calcu- lated using the formula w × 100:l (Fig. 3); considering the Material and its description incomplete preservation of the aptychi, our measurements are approximated as well. The collections studied are housed As mentioned above, aptychi come from two concretions in the Paleontological Institute, Russian Academy of Sci- found at the same stratigraphic level. Our material contains ences (PIN) and in the Staatliches Museum für Naturkunde three morphotypes of aptychi: (1) wide in the basal part with Stuttgart, Germany (SMNS).

Fig. 3 Whorl cross sections of Leioceras from level with aptychi (specimen no. PIN 5611/1 A), and reconstruction (photomontage) of bivalved aptychus (of the specimen no. PIN 5611/5, B), with measured dimensions

1 3 First fnd of aptychi of Leioceras and Bredyia (Ammonoidea; Aalenian, Russia)

The aptychus of morphotype I is represented by an iso- terminally. The length of the symphysis apparently reached lated valve, in which a third of the terminal part is partly 12.5 mm and the valve width 6.6 mm; the width-to-length shattered or partly missing (Fig. 4). Only the black organic index is 52.8. The apical angle (formed by the symphysis layer with well-developed growth lines is preserved. and inner margins) is slightly less than 90°. The symphysis is marked by a smooth fange delineated Another aptychus, which we assign to morphotype II from the convex aptychus wall and noticeably widening (Fig. 5), also lacks the terminal part, and the margins are

Fig. 4 Part of concretion with aptychus morph I (specimen no. PIN 5611/2): A aptychus, B Leioceras opalinum (Reinecke) [m], C general view. Scale bars = 10 mm

1 3 V. V. Mitta et al.

Fig. 5 Aptychus morph II (specimen no. PIN 5611/3): A aptychus, scale bar = 5 mm; B part of subterminal area, SEM image, scale bar = 1 mm; C part of subsymphysal area, SEM image, scale bar = 1 mm (cl calcareous layer, ol organic layer) covered by the rock matrix. A smooth fange on the con- convex part (Fig. 6B) contains mainly the black organic necting margin is also prominent, with noticeable expan- layer with remains of the calcareous layer, and the con- sion from the basal to terminal areas. Most of the aptychus cave counterpart is represented by the inner side of the only has a black organic layer. However, from the middle of yellowish-brown calcareous layer (Fig. 6A). The imprint the aptychus and further on to the terminal region there are with the calcareous layer clearly shows the outline of the areas of a reddish-yellow outer calcareous layer overlying terminal part of the outer margin; a fange along the sym- the black organic layer, with thicker and more prominent physis. The basal part of the aptychus is covered by the growth lines. The length of the symphysis was apparently rock matrix. The length of the symphysis is 11 mm and 8 mm, the width of the valve was 4 mm; the width-to-length the valve length is apparently 4.3 mm; the width-to-length index was 50, apical angle ~ 70°. index is 39 and the apical angle is ~ 70°. A further aptychus of morphotype II is represented by The opposite side of the same piece of concretion exhib- approximately the same part of the isolated valve (Fig. 6A, its small fragments of a paired aptychus of morphotype III B). The aptychus fractured along the boundary between (Fig. 6C), which was destroyed during preparation, and the calcareous and organic layers. Consequently, the

1 3 First fnd of aptychi of Leioceras and Bredyia (Ammonoidea; Aalenian, Russia)

Fig. 6 Part of concretion with aptychi (specimen no. PIN 5611/4): A imprint of aptychus morph II with preserved calcareous layer (cl), B its positive part with preserved organic layer (ol), C remains of aptychus morph III on the opposite side of the concretion. Scale bar = 10 mm is represented by the basal part with a yellowish-brown supposedly of an upper jaw, with an organic layer, frac- calcareous layer. tured in the manner of desiccation cracks (Fig. 7B). Other The isolated valve of an aptychus of morphotype III remains of a fractured organic layer are preserved in the of a much better preservation was found in another piece basal part of the concave counterpart (Fig. 7C), which, in of the concretion (Fig. 7). This aptychus is also fractured general, demonstrates the inner surface of the calcareous at the boundary between the organic and calcareous lay- layer with thin growth lines. Remains of the organic layer ers. The convex ‘positive’ part mainly has the preserved with growth lines are preserved along the symphysis of black organic layer, but the remains of the ca. 0.1-mm- the concave counterpart including the connecting fange thick outer calcareous layer are visible along the outer (Fig. 7D). The length of the symphysis is 9 mm and the region, the margin of which is covered by the rock matrix. valve width apparently reached 3 mm; the width-to-length The dented region of the convex valve shows a fragment, index is 33. An attempt to reconstruct a complete paired

1 3 V. V. Mitta et al.

Fig. 7 Aptychus morph III (specimen no. PIN 5611/5): A apty- 1 mm; D subterminal area of counterpart of valve, SEM image, scale chus, scale bar 5 mm; B possible upper jaw, SEM image, scale bar bar = 1 mm (cl calcareous layer, ol organic layer, uj possible upper 500 µm; C basal area of counterpart of valve, SEM image, scale bar jaw) aptychus based on this specimen and its imprint is given (: Hammatoceratinae). Therefore, the in Fig. 3B. aptychi described above most likely belong to Leioceras When this study was almost completed, preparation of and Bredyia. some ammonites revealed Leioceras with an imprint of the Species of the genus Bredyia, including B. subinsignis outer side of an aptychus valve in the aperture of the micro- (Oppel; Schweigert 1996: pl. 1, fgs. 1, 2; pl. 2, fg. 1), conchiate body chamber, with a preserved fragment of the usually have a subtrapezoidal cross section with a vertical calcareous layer (Fig. 8). This fnd comes from the strati- umbilical wall and a rounded-angular transition to the lat- graphic level 0.2 m above the base of the section. Based on eral side, which agrees well with aptychi of morphotype I. the valve length-to-width ratio, this aptychus also belong to The width-to-length index calculated from 5 specimens of morphotype III. Bredyia from 15 to 32 mm in diameter from the concretions with aptychi ranges from 56 to 64, with the width-to-length index of the aptychus illustrations in Fig. 4 nearing 53. Con- Discussion and conclusions sidering the incomplete state of preservation of the material and the measurement error, it is possible that morphotype I The concretions with aptychi also contain ammonite belongs to the genus Bredyia. conchs of the genera Leioceras Hyatt, 1867 (Grapho- Lepsius (1875: pl. 2, fg. 4) illustrated an aptychus valve ceratidae: Leioceratinae) and Bredyia Buckman, 1910 that was preserved in situ in the body chamber of Leioceras,

1 3 First fnd of aptychi of Leioceras and Bredyia (Ammonoidea; Aalenian, Russia)

Fig. 8 Leioceras opalinum (specimen no. PIN 5611/6; A), with remains of aptychus morph III in an apertural part of body chamber (B). Scale bar = 10 mm judging from the umbilicus width, of a macroconchiate An unfgured aptychus from beds with Leioceras comptum specimen (refgured by Trauth 1930: pl. 3, fg. 16). Aptychi near Balingen in Southern Germany (Rieber 1963: p. 28), of morphotype II only difer in the smaller size from this judging from the description and size, also belongs to micro- aptychus, the only one reliably published from the Lower conchs of Leioceras. Aalenian in the modern concept. Two cornaptychi from the Buckman (1891 in Buckman 1987–1907: p. 262, pl. Lower Aalenian of Northern Switzerland, one of which sur- 45, fgs. 11, 12) fgured an aptychus valve found in the vived in situ in the body chamber of Leioceras, are depicted body chamber of a small (maximum diamater = 23 mm) in an unpublished thesis by Etter (1990). specimen of Dumortieria subundulata (Branco; refgured Additionally, two ex situ aptychi from the Lower Aal- by Trauth 1930: pl. 3, fg. 14) from the upper Toarcian enian Opalinum Zone of southwestern Germany (Fig. 9) are (Dumortieria pseudoradiosa Zone) in its modern under- well comparable to the material from North Caucasus. They standing. This specimen from Southern England (Penn come from the clayey Opalinuston Formation and were asso- Wood) is similar in the shape of the valve to our aptychi ciated with Leioceras opalinum (Reinecke), Pleurolytoceras of morphotype II (the width-to-length index based on our torulosum (Zieten) and P. dilucidum (Oppel), indicating a measurements of the illustration is 43), at the same time lowermost Aalenian age. In contrast to the Caucasian mate- difering in the course of the growth lines and in the fange rial, the bigger-sized aptychus shows the ornamentation along the symphysis—it is the same width along the entire of the outer calcitic layer, which is tuberculated. Hence, length from the basal to terminal regions. However, these our aptychi of morphotype II belong to macroconchiate diferences could result from an inaccurate drawing of the Leioceras. aptychus from England. Among published illustrations, In our view, the afnity of aptychi of morphotype III to the specimen from the Toarcian Posidonia Shale of Holz- the genus Leioceras is also evident. Long narrow valves maden (Germany) fgured by Farinacci et al. (1976: pl. 1, agree well with the shape of the microconchs of this genus. fg. 8) is similar to specimens from the Northern Caucasus

1 3 V. V. Mitta et al.

Fig. 9 Aptychi of Leioceras opalinum from the Opalinum Zone/Subzone of Heiningen, SW Germany: specimen no. SMNS 70424-1 (A); speci- men no. 70424-2 (B). Scale bar = 10 mm

in the shell shape and ornamentation. SEM photographs References apparently of the same specimen (Farinacci et al. 1976: pl. 6, fgs. 10, 11) also show a similar micro-ornamentation. Arkell, W.J. 1957. Aptychi. In Treatise on Invertebrate Paleontology. Pt. L. Recent workers consider that cornaptychi difer from , ed. R.C. Moore. New York, Kans: Geological Society of America, Lawrence, University of Kansas Press. another types of aptychi in the presence of a well-defned Besnosov, N.V. 1967. Bajocian and Bathonian deposits of the North- organic fold between the valves (a fange along the sym- ern Caucasus. Trudy Vsesoyuznogo nauchno-issledovatelskogo physis observed in our material) and composed of a set instituta nefti i gaza, [Proceedings of All-Russian Scientifc Research Oil and Gas Institute] of mineralized layer above a single organic layer (e.g. 28 (36): 1–179. (in Russian). Besnosov, N.V., V.P. Kazakova, G.P. Leonov, and D.I. Panov. 1960. Lehmann 1976; Engeser and Keupp 2002). Results of Stratigraphy of the Lower and Middle Jurassic deposits of detailed study of cornaptychi are presented by Farinacci the central part of Northern Caucasus. Materialy po geologii et al. (1976). In our material, the outer layer is represented gasonosnykh raionov SSSR. Trudy Vsesoyuznogo nauchno- issledovatel’skogo instituta prirodnykh gazov [Proceedings of by only a single calcareous layer; possibly, this preser- All-Russian Scientifc Research Institute] 10 (18): 109–190. (in vation can be explained by diagenetic alteration occur- Russian). ring within sideritic concretions. However, Trauth (1930) Buckman, S.S. 1887–1907. A monograph of the ammonites of the accepted for his ‘cornaptychus’ group aptychi with two or “Inferior Oolite Series”. Palaentographical Society Monographs three calcareous layers, or sometimes only with a single 1: cclxii + 1–456. Buckman, S.S. 1910. Certain Jurassic (Inferior Oolite) specimens of one. ammonites and Brachiopoda. Quarterly Journal of the Geologi- Judging from the information summarized above, we cal Society of London 66: 90–108. regard that the Lower Aalenian aptychi of the Northern Callomon, J.H. 1985. The evolution of the Jurassic ammonite fam- Palaeontology, Special Paper Caucasus belong to microconchs of Bredyia and macro- ily Cardioceratidae. 33: 49–90. Leioceras Chandler, R.B., and J.H. Callomon. 2009. The Inferior Oolite at conchs and microconchs of . Coombe Quarry, near Mapperton, Dorset, and a new Middle Jurassic ammonite faunal horizon, Aa-3b, Leioceras compto- Acknowledgements This study was supported by the Program of costosum n. biosp., in the Scissum Zone of the Lower Aalenian. Presidium of the Russian Academy of Sciences no. 28. Roman Rakitov Proceedings of the Dorset Natural History and Archaeological (Paleontological Institute, Moscow) helped with the SEM photogra- Society 130: 99–132. phy (Tescan Vega). The English text was checked by M.V.L. Barclay Closs, D. 1967. Goniatiten mit Radula und Kieferapparat in der (Natural History Museum, London). The authors are sincerely grateful Itararé-Formation von Uruguay. Paläontologische Zeitschrift to everyone who assisted in this work. Finally, our cordial thanks go to 41: 19–37. the journal’s referees Horacio Parent (University of Rosario, Argentina) Contini, D. 1969. Les Graphoceratidae du Jura franc-comtois. and an anonymous one as well as the responsible editors Christian Klug Annales scientifques de l’Université de Besanşon, série 3. (University of Zurich, Switzerland) and Mike Reich (SNSB-BSPG Géologie 7: 1–95. Munich, Germany).

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