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Characterization of Two New Superorders Nautilosiphonata and Calciosiphonata and a New Order Cyrtocerinida of the Subclass Nauti

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Characterization of Two New Superorders Nautilosiphonata and Calciosiphonata and a New Order Cyrtocerinida of the Subclass Nauti GFF ISSN: 1103-5897 (Print) 2000-0863 (Online) Journal homepage: http://www.tandfonline.com/loi/sgff20 Characterization of two new superorders Nautilosiphonata and Calciosiphonata and a new order Cyrtocerinida of the subclass Nautiloidea; siphuncular structure in the Ordovician nautiloid Bathmoceras (Cephalopoda) Harry Mutvei To cite this article: Harry Mutvei (2015) Characterization of two new superorders Nautilosiphonata and Calciosiphonata and a new order Cyrtocerinida of the subclass Nautiloidea; siphuncular structure in the Ordovician nautiloid Bathmoceras (Cephalopoda), GFF, 137:3, 164-174, DOI: 10.1080/11035897.2015.1061592 To link to this article: http://dx.doi.org/10.1080/11035897.2015.1061592 Published online: 08 Oct 2015. Submit your article to this journal Article views: 23 View related articles View Crossmark data Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=sgff20 Download by: [Naturhistoriska Riksmuseum] Date: 24 November 2015, At: 02:01 GFF, 2015 Vol. 137, No. 3, 164–174, http://dx.doi.org/10.1080/11035897.2015.1061592 Article Characterization of two new superorders Nautilosiphonata and Calciosiphonata and a new order Cyrtocerinida of the subclass Nautiloidea; siphuncular structure in the Ordovician nautiloid Bathmoceras (Cephalopoda) HARRY MUTVEI Mutvei, H., 2015: Characterization of two new superorders Nautilosiphonata and Calciosiphonata and a new order Cyrtocerinida of the subclass Nautiloidea; siphuncular structure in the Ordovician nautiloid Bathmoceras (Cephalopoda). GFF, Vol. 137 (Pt. 1, September), pp. 164–174. q Geologiska Fo¨reningen. doi: http://dx.doi. org/10.1080/11035897.2015.1061592. Abstract: Based on differences in the siphuncular structures, the subclass Nautiloidea is divided into two new superorders: Nautilosiphonata and Calciosiphonata. The first superorder is characterized by the nautilus-type of connecting rings, and the second superorder by calcified-perforate type of the connecting rings. A new order Cyrtocerinida is erected for the families Bathmoceratidae, Cyrtocerinidae and Eothinoceratidae, previously included in the order Ellesmeroceratida. The siphuncular structure in the Ordovician nautiloid Bathmoceras holmi n. sp. is described. It is characterized by (1) connecting rings that are composed of an outer, calcareous, spherulitic–prismatic layer and an inner, fibrous, chitinous layer, and (2) prominent siphuncular ridges that originate from the inner surfaces of the connecting rings. The structure of the siphuncular ridges in Bathmoceras is compared with that of the actinosiphonate lamellae in the Silurian oncocerid nautiloid Octamerella. Keywords: Palaeozoic nautiloid cephalopods; siphuncle; superorders Nautilosiphonata; Calciosiphonata; order Cyrtocerinida; Bathmoceras Department of Palaeobiology, Swedish Museum of Natural History, Box 50007, SE-10405 Stockholm, Sweden; [email protected] Manuscript received 8 January 2015. Revised manuscript accepted 9 June 2015. Introduction Recent studies (summarized in Mutvei 2002a, 2002b) show that Holm (1899) was the first to give a correct and detailed nautiloids are divided into two groups that have different types description of the shell structure in Bathmoceras sp. from the of siphuncular structures: (1) the nautilus-type, and (2) the Middle Ordovician in Sweden. In the present report, the calcified-perforate type. The first type is characterized by siphuncular structure is described in Bathmoceras holmi n. connecting rings that each is composed of an outer, calcareous, sp. from the Middle Ordovician of Estonia and it is compared Downloaded by [Naturhistoriska Riksmuseum] at 02:01 24 November 2015 spherulitic–prismatic layer and an inner, fibrous, chitinous layer with that in Bathmoceras sp. (Holm 1899) and that in the that generally is destroyed by diagenesis. In the calcified- Silurian oncocerid nautiloid Octamerella (Mutvei 2011, 2013). perforate type, the inner fibrous layer of the connecting ring is replaced by a calcareous layer that is perforated by cavities and pore canals. The first group of nautiloids is here placed in a new Material and methods superorder Nautilosiphonata and the second group of nautiloids The material studied in the present paper comprises the in a new superorder Calciosiphonata. following specimens. During the Ordovician, nautiloid cephalopods underwent an explosive evolutionary phase and, as a result, numerous new (1) One well-preserved shell of Bathmoceras (specimen no. taxa appeared (Kro¨ger & Landing 2008;Kro¨ger et al. 2009a). Mo. 151247, deposited at the Swedish Museum of Natural One new taxon was Bathmoceras of the family Bathmoceratidae History, Department of Palaeobiology, Stockholm), here that appeared in the Middle Ordovician. Flower (1964) and Chen assigned to the new species B. holmi. It was collected by & Teichert (1987) assigned the family Bathmoceratidae to the Mikwitz in the 19th century from the uppermost part of the suborder Cyrtocerinina in the order Ellesmeroceratida. How- Middle Ordovician Kundan stage at Tallinn, Estonia. ever, the siphuncular structure in cyrtocerinids is much more It consists of a 10.0 cm long section of a phragmocone specialized than that in ellesmerocerids. The cyrtocerinids are with 30 chambers and a 4.0 cm long section of a nearly therefore placed in a new order Cyrtocerinida. complete body chamber (Fig. 1(A)). It was studied by GFF 137 (2015) Mutvei: Characterization of two new superorders 165 Downloaded by [Naturhistoriska Riksmuseum] at 02:01 24 November 2015 166 Mutvei: Characterization of two new superorders GFF 137 (2015) G. Holm who made 20 vertical and transverse sections of the calcified-perforate type. All hitherto made studies show distinct siphuncle and prepared three plates with illustrations that differences between these two types. Each type has numerous were printed by Holm but never published. The original subtypes that characterize different taxonomic groups. plates and photographs are stored at the Swedish Museum of Nautiloids with the first type of siphuncles are placed in the Natural History, Stockholm. Five of Holm’s original new superorder Nautilosiphonata and nautiloids with the second illustrations are selected and included in the present paper siphuncle-type in the new superorder Calciosiphonata. The two (Fig. 1(A)–(E)). These illustrations show the original shape superorders are known as far back as the late Cambrian when of the specimen before sectioning, and detailed three- they comprised the ellesmerocerid-like nautiloids with the dimensional reconstruction of the siphuncle. Unfortunately, nautilus-type of siphuncles and the plectronocerid nautiloids Holm did not leave any notes or descriptive captions to the with the calcified-perforate type of siphuncles (Mutvei et al. plates. 2007). (2) The second studied shell was described by Holm (1899) as Bathmoceras sp. (specimen SGU, Ser. C. no. 179, New superorder Nautilosiphonata deposited at the Swedish Geological Survey, Uppsala). It was The septal necks in this suborder are either orthochoanitic, collected at the boundary between the Hunderumian and holochoanitic or cyrtochoanitic. The connecting rings are of the Valastean substages of the Middle Ordovician Kundan stage nautilus-type and are composed of a calcareous, spherulitic– (see Jaanusson & Mutvei 1982; Mutvei 1996) on the island of ¨ prismatic layer on the outer surface of the septal neck, and an Oland, Sweden. It is preserved as a 7.0 cm long and 3.0 cm inner, fibrous, chitinous layer that is a non-mineralized broad section of the ventral side of a phragmocone (Holm continuation of the nacreous layer of the septal neck. The latter 1899, pl. 5). Of this small specimen, Holm cut 25 longitudinal layer is typically destroyed by diagenesis. In addition to the and transverse sections of the siphuncle, several of which are Nautilus, this siphuncular-type is present in the orders Nautilida, 1.0–2.0 mm thick (Holm 1899, pls. 5–8). It is unknown how Tarphycerida, Ellesmerocerida, Discocerida, Oncocerida, new Holm was able to cut so many and such thin sections. order Cyrtocerinida and probably also in Ascocerida (Mutvei (3) The V-shaped ventral sinuses of the suture lines are 2002a, 2011, 2013; Mutvei & Stumbur 1971; Mutvei & Dunca illustrated in Bathmoceras linnarsoni Angelin & Lindstro¨m 2011, Mutvei et al. 2010; Stumbur & Mutvei 1983; Hewitt & (1880, pl. 16, fig. 4, specimen no. Mo. 150046) from the Stait 1985; Evans & King 1990;Kro¨ger 2012; Kro¨ger & Mutvei orthocerid limestone, Ordovician, Va¨stergo¨tland, Kinne- 2005;Kro¨ger & Landing 2008;Kro¨ger et al. 2009a, 2009b; kulle, Sweden. Nielsen et al. 2009). The orders Ellesmerocerida, Discosorida, (4) The structure of the siphuncular lobes in Bathmoceras is oncocerida and probably also Ascocerida, are closely related and compared with that of the actinosiphonate lamellae in the belong to the superorder Multiceratoidea that, in addition to the Silurian oncocerid nautiloids: (a) Octamerella sp. (Mo. nautilus-type of the siphuncle, is characterized by short body 5835, previously illustrated in Mutvei 2011, figs. 3–7) from chamber, more or less constricted aperture at terminal growth the Llandoverian Lower Visby mudstone, (b) Octamerella stage, and multiple muscle scars at the base of the body chamber. cf. pugil (Mo. 152127, previously illustrated in Mutvei 2011, Also Tarphycerida with longer body chamber probably belongs fig. 2B,C) from the Wenlockian Hemse Beds, Mannaga˚rda, to the Multiceratoidea. The genus Bathmoceras
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