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Digestive Structures in the Middle Ordovician Trilobite Prionocheilus Rouault 1847, from the Barrandian Area of Czech Republic

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Digestive Structures in the Middle Ordovician Trilobite Prionocheilus Rouault 1847, from the Barrandian Area of Czech Republic Geologica Acta, Vol.16, Nº 1, March 2018, 65-73 DOI: 10.1344/GeologicaActa2018.16.1.4 O. Fatka and P. Budil, 2017 CC BY-SA Digestive structures in the Middle Ordovician trilobite Prionocheilus ROUAULT 1847, from the Barrandian area of Czech Republic O. FATKA1 P. BUDIL2 1Charles University, Faculty of Sciences, Institute of Geology and Palaeontology Albertov 6, 128 43, Prague, Czech Republic. E-mail: [email protected] 2Czech Geological Survey Klárov 3, 118 21, Prague, Czech Republic. E-mail: [email protected] ABS TRACT Remains of a digestive system from a slightly damaged articulated specimen of the comparatively rare bathycheilid trilobite Prionocheilus vokovicensis (ŠNAJDR, 1956) are described for the first time. The specimen comes from the Middle Ordovician Šárka Formation of the Prague Basin and contains the midgut region of the digestive system preserved through the axial region of glabella and six anterior thoracic segments. The anterior-most part of the digestive system is unknown as the anterior glabellar lobes are not preserved in the studied specimen. In the cephalic shield, the remains of two pairs of gut diverticulae are seen in the posterior region of the glabella. Remains of five pairs of small cavities developed in the axis of the first six thoracic segments represent the remains of thoracic gut diverticulae. The discussed specimen possess the first undoubted remain of digestive structures established within the family Bathycheilidae (Přibyl, 1953). KEYWORDS Prionocheilus. Digestive tract. Ordovician. Barrandian area. Czech Republic. INTRODUCTION and Bohdalec (Katian) fms. of the Prague Basin (for summary see Fatka et al., 2014) (Fig. 1C). Nearly one thousand trilobite species have been described from the Cambrian to Devonian aged rocks Here, we describe the morphology of the digestive of the Barrandian area of the Czech Republic (Valíček system in the rare bathycheilid trilobite Prionocheilus and Vaněk, 2001; Vaněk and Valíček, 2002) but vokovicensis (ŠNAJDR, 1956). A slightly damaged internal remains of soft parts are extremely rare (e.g. Šnajdr, mould of an originally complete and well articulated 1990; Fatka et al., 2014). About twenty exceptionally exoskeleton was recently identified by the junior author preserved articulated trilobite exoskeletons with in collections housed in the National Museum of Prague remains of digestive system have been collected from (housed under the inventory number NM L35774). The Cambrian Buchava and Jince formations (fms.) of the external mould of the studied specimens is not stored in the Skryje-Týřovice and Příbram-Jince basins (Jaekel, National Museum collections. This extraordinary specimen 1901; Fatka et al., 2014). Similar number of trilobite was collected near the town of Rokycany, particularly in the specimens with undoubted remains of gut, cephalic fields of the Osek locality. In these fields, diverse Middle and thoracic diverticulae and/or crop were recently Ordovician fossils, preserved in silicified nodules of the documented in Ordovician specimens from the Mílina Šárka and Dobrotivá fms., have been collected since the (Tremadocian), Šárka (Darriwilian), Letná (Sandbian), middle of the 19th century (Lajblová and Kraft, 2014). 65 O. Fatka and P. Budil Digestive structures in Prionocheilus N GLOBAL REGIONAL SPECIES A Bohemian Massiv AGE TS STAGES TU STAGES FORMATIONS ST SLICES SERIES SYSTEM Hi2 HIRNANTIAN 6c 21 KOSOVIAN KOSOV Hi1 6b 20 Ka4 6a 19 KRÁLUV R KRALODVORIAN DVUR E Ka3 18 KATIAN 5d BOHDALEC PP Ka2 17 U ZAHOŘANY CZECH Ka1 5c 16 BEROUNIAN VINICE REPUBLIC Sa2 5b 15 LETNÁ N SANDBIAN LIBEŇ Sa1 5a 14 IA DOBROTIVIAN DOBROTIVÁ Dw3 4c 13 12 DARRIWILIAN Dw2 4b ORETANIAN LE ŠÁRKA 11 Prionocheilus borni Dw1 4a 10 PRAHA s Prague Basin Dp3 B M I D 3b 9 Prionocheilus pulcher DAPINGIAN Dp2 O R D V I C Dp1 3a ARENIGIAN BEROUN 8 KLABAVA Prionocheilus derceto 2c Prionocheilus mendax 0 10 Fl3 7 ZDICE FLOIAN 2b km R Fl2 6 Fl1 2a 5 MÝTO W E Silurian and Devonian 1d Prionocheilus vokovicensi LO Tr3 4 1c MÍLINA Ordovician TREMADOCIAN Tr2 1b 3 TREMADOCIAN TŘENICE ROKYCANY Fossil locality 2 Tr1 1a C 1 FIGURE 1. Maps showing the location of the discovery site and Ordovician stratigraphy in the Barrandian area: A) Map of the Czech Republic and the Bohemian Massif with the Ordovician rocks of the Barrandian area; B) Ordovician of the Prague Basin showing the location of the Osek locality at which the studied specimen was found. C) Chart showing the correlation between global series, stages, stage slices, Time Slices (TS), Time Units (TU), and the regional chronostratigraphic and lithostratigraphic units recognized in the Ordovician of the Prague Basin with marked ranges of the species of Prionocheilus (stratigraphy modified from Bergström et al., 2008; Fatka et al., 2013). Ranges of the species of Prionocheilus based on Šnajdr (1956), Vaněk (1965), Budil and Kraft (2003), Mergl et al. (2008), Peršín and Budil (2009), Vokáč et al. (2015). GEOLOGICAL SETTING dark shales. Our knowledge about fauna is generally based on specimens collected from siliceous nodules, which have The Šárka Formation attracted the attention of amateur collectors. However, such loose nodules do not provide information about the The Šárka Formation (Fm.) contains a highly diverse stratigraphic position and original palaeoenvironment (Budil skeletal fauna (e.g. Havlíček and Vaněk, 1966, 1990; Fatka et al., 2007; Mergl et al., 2008). and Mergl, 2009). The thickness of this formation ranges from several metres in the marginal parts of the basin to nearly Fossil associations 300 metres in segments of supposed rapid synsedimentary subsidence (Havlíček, 1981). The stratigraphy and Abundant remains of brachiopods, gastropods, trilobites, depositional setting of the Šárka Fm. have been discussed by agnostids, phyllocarids, ostracods, bivalves, hyoliths, numerous authors (e.g. Kukal, 1962; Havlíček and Vaněk, cephalopods, echinoderms, and conulariids associated 1966; Kraft and Kraft, 1992, 1999; Havlíček and Fatka, 1992; with graptolites and ichnofossils have been studied for Havlíček, 1998; Servais et al., 2008). In earlier schemes, the more than 150 years (Barrande, 1872; Havlíček and Vaněk, Šárka Fm. was correlated with the British Llanvirn Series 1966; Chlupáč, 1970, 2003; Mikuláš, 1991; Horný, 2001; (e.g. Havlíček and Vaněk, 1966); later, it was supposed to Mergl, 2002; Kraft and Kraft, 2003; Budil et al., 2007; correspond to the late Arenig to early Llanvirn interval (e.g. Manda, 2008; Mergl et al., 2008; Fatka and Mergl, 2009; Kraft et al., 2001). Fatka et al. (2013) correlated the Šárka Steinová, 2012; Polechová, 2013; Aubrechtová, 2015). Fm. with the Oretanian Regional Stage which is equal to the The intensively studied and diverse fauna made possible to middle Darriwilian (Bergström et al., 2008). Based on the distinguish several trilobite and non-trilobite associations of restricted ranges of graptolites, the Šárka Fm. has been divided the Šárka Fm. (Havlíček, 1982, 1998; Havlíček and Vaněk, into two biozones: the older Corymbograptus retroflexus and 1990; Mergl, 2002; Lefebvre, 2007). Mikuláš (1991, 1998) the younger Didymograptus clavulus biozones (Kraft et al., studied assemblages of ichnofossils, which he assigned to a 2001). The Šárka Fm. typically consist of poorly fossiliferous transition from Cruziana to Zoophycos ichnofacies. Geologica Acta, 16(1), 65-73 (2018) 66 DOI: 10.1344/GeologicaActa2018.16.1.4 O. Fatka and P. Budil Digestive structures in Prionocheilus Trilobite associations surface of the internal mould (Microscope NIKON SMZ 1500, Leica S8APO); photographs were taken More than 50 species of trilobites have been described using digital cameras (a NIKON D 300 and an Olympus from the Šárka Fm. (Havlíček and Vaněk, 1966; Budil et al., SZX-ILLB200) after coating with ammonium chloride. 2007; Mergl et al., 2007). Remains of trilobite exoskeletons The drawing was made from a photograph using Corel together with gastropod, brachiopod and bivalve shells are Draw X3 and Adobe Photoshop CS5. The terminology common elements in fossil associations. Trilobite associations used follows that proposed by Whittington and Kelly have been discussed by Havlíček and Vaněk (1990), Havlíček (1997), including the following abbreviations: sag. (1998), Bruthansová (2003), Budil et al. (2007), Mergl et al. (sagittal), tr. (transverse). The specimen is housed in (2008), Fatka and Mergl (2009) and Mergl and Kozák (2016). the National Museum of Prague, under the inventory All earlier proposals of trilobite associations were recently number NML 35774. summarized by Fatka et al. (2015) and are shown in Figure 2. The discussed damaged internal mould of an originally SYSTEMATIC PALAEONTOLOGY complete exoskeleton of Prionocheilus vokovicensis is preserved in a siliceous nodule that is known from the shallower Family: Bathycheilidae Přibyl, 1953 part of the Placoparia Association of the Šárka Fm. (Fig. 2). Subfamily: Pharostomatinae HUPÉ, 1953 GENUS Prionocheilus Rouault, 1847 METHODS Type of species. Prionocheilus verneuili (Rouault, 1847), Sandbian/Katian, Formation de Riadan in the Methods used to analyse the trilobite specimen Martigné-Ferchaud South of Rennes, Caradocian, Brittany, included standard light microscopy of the external France (by original designation). poor orthid brachiopods Placoparia Association Cyclopygid Biofacies planktonic graptolites dendroid “gardens ” caryocaridids Mitrocystitid Biofacies Lagynocystitid Biofacies Paterula Association Prionocheilus FIGURE 2. Sketch representing the distribution
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