First Find of Aptychi of Leioceras and Bredyia (Ammonoidea
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PalZ https://doi.org/10.1007/s12542-018-0416-6 RESEARCH PAPER First fnd of aptychi of Leioceras and Bredyia (Ammonoidea, Hildoceratoidea) in the Aalenian 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 Germany. Keywords Aalenian · Ammonites · Cephalopod 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 Jurassic and Cre- appendage in the body chamber of the Late Cretaceous 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 Middle Jurassic (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 Toarcian 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 France (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 Hammatoceras upper Toarcian Dumortieria 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.