Swiss J Palaeontol (2016) 135:139–151 DOI 10.1007/s13358-015-0110-1 Patterns of the evolution of aptychi of Middle Jurassic to Early Cretaceous Boreal ammonites 1 1 Mikhail A. Rogov • Aleksandr A. Mironenko Received: 27 March 2015 / Accepted: 1 November 2015 / Published online: 27 November 2015 Ó Akademie der Naturwissenschaften Schweiz (SCNAT) 2015 Abstract Here we are providing a review of aptychi Stephanoceratoidea and Perisphinctoidea have aptychi records in ammonites of Boreal origin or that inhabited significantly smaller than the aperture diameter. Boreal/Subboreal basins during the Bathonian–Albian with special focus on new records and the relationship between Keywords Aptychi Á Jurassic Á Cretaceous Á Ammonites Á the evolution of ammonite conch and aptychi. For the first Evolution time we figure aptychi that belong to Aulacostephanidae, Virgatitidae, Deshayesitidae, Craspeditinae and Laugeiti- nae. A strong difference between aptychi of micro- and Introduction macroconchs of co-occurring Aspidoceratidae is shown, which, along with their shell morphologies suggests niche Aptychi are organic (in some cases with calcite layers of divergence of these dimorphs. Aptychi of Aptian Sinzovia variable thickness) and usually bivalved plates, associ- (Aconeceratidae) should be tentatively ascribed to Diday- ated with ammonites and considered as parts of the lower ilamellaptychus, while their previous assignment to rhyn- jaws albeit other functions are also widely discussed chaptychi was caused by misidentification. Aptychi of (Parent et al. 2014). During the nearly 200-year history Middle Jurassic–Early Cretaceous Boreal and Subboreal of aptychi research, a great number of formal species and ammonites are characterized by a very thin calcareous non- genera have been described. However, only uncommon porous outer layer lacking distinct ribs and tubercles (only records of aptychi were mentioned from the Boreal radial striae sometimes occur), and mainly should be Middle Jurassic to Early Cretaceous (e.g. Blake 1875; assigned to Praestriaptychus. Some ammonoid groups (i.e. Weerth 1884), and aptychi of many ammonite groups Ancylocerina and Desmoceratoidea) are characterized by (especially of those with Boreal and Subboreal affinities) the presence of different aptychi types irrespective of their remain unknown until now. Significant progress in the shell shape. This fact could indicate that bivalved praes- study of Boreal aptychi has been achieved over the last triaptychi could have easily transformed into single-valved decades in which numerous aptychi (including in situ ‘‘anaptychi’’ and vice versa. Size and form of aptychi in findings in ammonoid body chambers) were described relation to those of the aperture of ammonite conchs vary and/or figured (cf. Etches and Clarke 1999; Engeser and within different lineages and at least some Keupp 2002; Rogov and Gulyaev 2003; Rogov 2004a, b; Mitta and Keupp 2004; Keupp and Mitta 2013; Miro- nenko 2014). Aptychi–ammonite conch associations sometimes are used for reconstructing ammonite evolu- & Mikhail A. Rogov tion (Trauth 1927; Engeser and Keupp 2002). However, [email protected] aptychi records are still significantly incomplete, and the Aleksandr A. Mironenko ammonite phylogenetic tree based on aptychi distribution [email protected] contradicts some aspects of phylogenies based on other 1 Geological Institute of RAS, Pyzhevski Lane 7, Moscow, features, especially the sutural development (Rogov Russia 119017 2004a, b). 140 M. A. Rogov, A. A. Mironenko Material correlation with international Tithonian and Berriasian stages remains unclear. In this study, we focus on little-known aptychi from Boreal Studied specimens are stored in the Moscow State and Subboreal areas (Fig. 1). Most of the studied speci- University Museum (MSU) and Vernadsky State Geolog- mens have been collected by the authors, and some spec- ical Museum of the Russian Academy of Sciences (SGM), imens or photos of aptychi were transferred to us by both in Moscow, Russia, with exception of those specimens colleagues. Studied aptychi were discovered within the which are available as photos thanks to the help of our body chambers of ammonites or ascribed to particular colleagues; the latter specimens are kept in the University ammonite groups due to their co-occurrences. As ammo- of Oslo (PMO, Norway), Cambridge Arctic Shelf Pro- nite diversity is relatively low in many stratigraphic levels gramme (CASP, Cambridge, UK) and Museum of Jurassic of the Boreal Jurassic (in many cases 1–2 genera belonging Marine Life (K, Kimmeridge, UK). to 1–2 families), such co-occurrences could help signifi- cantly even when aptychi are found separately from the conchs of the corresponding ammonite. In some cases (for Review and description of new aptychi records example, in suspected Middle Volgian virgatitid aptychi), a cross sections of ammonites versus aptychi relative length Stephanoceratoidea was also used to infer ammonite–aptychi relationships. In addition to newly collected material, we are also reviewing Cardioceratidae some recent records of aptychi in Boreal and Subboreal ammonites. Both in situ records of cardioceratid aptychi and their Systematics of higher ammonite taxa used herein is isolated occurrences are only known from the Lower based on Besnosov and Michailova (1991) with some Callovian of the European part of Russia (Mitta and Keupp additions from Kvantaliani et al. (1999) and Shevyrev 2004), while Late Callovian aptychi, which belong to (2006). As aptychi usually occurred outside the host conchs Quenstedtoceras, are also known from northern Poland and their relation to ammonoid taxa are unclear, generic (Lehmann 1972; Dzik 1986). Surprisingly, mass occur- and species names used for aptychi are separate from those rences of cardioceratids, which sometimes crowded the of ammonoid shells and treated as parataxa (Engeser and bedding planes in the Upper Oxfordian or Upper Kim- Keupp 2002). A brief description of major aptychi types is meridgian black shales are lacking cardioceratid aptychi, given by Engeser and Keupp (2002). albeit the Upper Oxfordian shales of the Kostroma region For the stages around the Jurassic/Cretaceous boundary, yielded perisphinctid aptychi. Taking reported uncalcified we are using the Volgian and Ryazanian as preferred cephalopod jaws into account, which co-occur with names, because these stages could be easily used for all numerous cardioceratids described by Dzik (1986) from the Boreal regions (cf. Rogov and Zakharov 2009), while their Upper Callovian of Poland and the absence of a calcitic Fig. 1 Map showing aptychi-bearing sites, specimens from which are Gorodischi, Ulianovsk, 10 Kashpir, Marievka, 11 Shirokij buerak, 12 figured or discussed. 1 Kuhn Island, 2 Janusfjellet Mt, Vasstak Elva, Kelevudagh Mt, 13 Veselovskaya 5 well, 14 Nordvik, 15 Cape Cape Festningen, 3 Sorkappland, 4 Kimmeridge Bay, 5 Eganovo, Hajryuzova Rybaki, 6 Ivanovskoe, Glebovo, 7 Mikhalenino, 8 Hvadukassy, 9 Patterns of the evolution of aptychi of Middle Jurassic to Early Cretaceous Boreal ammonites 141 layer in the Early Callovian ones, cardioceratid aptychi conch (Keupp and Mitta 2013, Fig. 13e). Similar aptychi could have been fully organic and their absence might be were also found within the body chamber of the Late primarily taphonomic in the Upper Jurassic. The shape of Bathonian Homoeoplanulites from NE Iran (Seyed-Emami cardioceratid aptychi allows them to be described as and Schairer 2011, Fig. 3B). A poorly preserved Praes- Praestriaptychus Trauth, 1927. triaptychus was also discovered associated with Elatmites (Grossouvriinae, Keupp and Mitta 2013, Fig. 21). Upper Kosmoceratidae Oxfordian clays and black shales, intensively studied in the Kostroma region of European Russia during the last decade Numerous occurrences of kosmoceratid aptychi have (Glowniak et al. 2010; Tesakova et al. 2012), are also become known since recently. Schweigert (2000) described known as a source of the suspected perisphinctid aptychi. an in situ record of Kosmogranulaptychus Rogov, 2004a Praestriaptychus was usually found in black shales as (originally referred by Schweigert to Granulaptychus isolated plates (Fig. 3f), but in situ findings are also known. Trauth, 1927) within the body chamber of Late Callovian The in situ occurrence of relatively small-sized Praestri- Kosmoceras. A few years later, the suggested kosmoceratid aptychus within the body chamber of Dichotomosphinctes aptychi, which were assigned to this family by co-occur- from the Upper Oxfordian Serratum Zone of Mikhalenino rence of conchs with corresponding aptychi, were descri- (Kostroma region, Fig. 2n) is the most interesting among bed from the Upper Bathonian (Mitta 2009) and Middle these records. Ataxioceratid ammonites were mainly typi- Callovian (Rogov 2004a, b) of the Russian Platform. cal for Sub-mediterranean areas, except their short-lived Finally, Keupp and Mitta (2013) described and illustrated Subboreal offshoot, separated as the subfamily Gravesiinae both isolated and well-preserved in situ aptychi of Early by Zeiss (in Fischer and Zeiss 1987). Aptychi were Callovian kosmoceratids. It should be noted that generic recorded in Early Volgian Gravesia gigas from Northern classification of kosmoceratid aptychi still remains unclear, France (Boulogne-sur-Mer, see Hahn 1963, pl. 13, Fig. 1), as in some cases, they are represented by internal moulds and isolated aptychi co-occurred with Gravesia gravesiana without any traces of a calcitic layer, thus they could be