Trepostome bryozoans from the Zahorany Formation (Upper Ordovician)

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Jun 4, 2013 - Abstract Three trepostome bryozoan species are descri- bed from the Upper Ordovician Zahorany Formation of. Lodenice, Prague Basin ...

Pala¨ontol Z (2014) 88:11–26 DOI 10.1007/s12542-013-0183-3

RESEARCH PAPER

Trepostome bryozoans from the Zahorˇany Formation (Upper Ordovician) of Lodeˇnice, Prague Basin, Czech Republic Andrej Ernst • Petr Kraft • Kamil Za´gorsˇek

Received: 17 December 2012 / Accepted: 8 May 2013 / Published online: 4 June 2013 Ó Springer-Verlag Berlin Heidelberg 2013

Abstract Three trepostome bryozoan species are described from the Upper Ordovician Zahorˇany Formation of Lodeˇnice, Prague Basin, Czech Republic. One genus is new—Lodenicella gen. nov. One species is described in open nomenclature. The described fauna contains ramose colonies or ramose branched projections from encrusting tubular-shaped colonies which inhabited shallow environment with moderate wave energy and significant influx of clastic material. Keywords Bryozoa  Trepostomata  Taxonomy  Morphology  Upper Ordovician  Prague Basin Kurzfassung Drei Arten der trepostomen Bryozoen werden aus der oberordovizischen Zahorˇany Formation von Lodeˇnice, Prager Becken, Tschechische Republik, beschrieben. Eine Gattung ist neu - Lodenicella gen. nov. Eine Art wird in offener Nomenklatur gefu¨hrt. Die beschriebene Fauna besteht aus ramosen Kolonien oder ramosen a¨stigen Auswu¨chsen von inkrustierenden rohrfo¨rmigen Kolonien, welche ein seichtes Milieu mit moderater Wellenenergie und erheblichem Eintrag von klastischem Material bewohnt haben. A. Ernst (&) Institut fu¨r Geowissenschaften der Christian-Albrechts-Universita¨t zu Kiel, Ludewig-Meyn-Str. 10, 24118 Kiel, Germany e-mail: [email protected] P. Kraft Institute of Geology and Palaeontology, Charles University in Prague, Albertov 6, 128 43 Praha 2, Czech Republic K. Za´gorsˇek Department of Paleontology, National Museum, Va´clavske´ na´m 68, 115 79 Prague, Czech Republic

Schlu¨sselwo¨rter Bryozoa  Trepostomata  Taxonomie  Morphologie  Oberordovizium  Prager Becken

Introduction The Prague Basin (Havlı´cˇek 1981) existed from the earliest Ordovician to late Middle Devonian. Its volcano-sedimentary infill of Tremadocian to Givetian age represents a denudation relic preserved in narrow linear subsiding depocentre (Havlı´cˇek 1998a). It was uplifted and deformed to a complicated synform during the Variscan orogeny (e.g. Havlı´cˇek 1981, 1998c). Now, its denudation relic is a part of the mostly unmetamorphosed Tepla´-Barrandian Unit (in a wide sense also informally known as Barrandian area) in the central Bohemian Massif (Czech Republic, Central Europe) (Fig. 1). In general, bryozoans represent accessory elements of the fossil associations of the Prague Basin. They are, however, locally common in some facies but completely missing from others. The richest bryozoan assemblages are found in the carbonates, especially in some of the Devonian limestone facies. On the other hand, in the shaly, clastic or volcanoclastic facies they are exceptional. That is why bryozoans do not belong to common fossils in Ordovician infill of the Prague Basin, as it is formed almost solely of noncarbonate rocks. However, there are carbonate or, at least, carbonate-rich intercalations or lenses at some Ordovician units. Such bodies have yielded more abundant, well-preserved and in some cases also diversified bryozoans. This is also the case of the fauna described herein. With the exception of the problematic bryozoan-like fossil Marcusodictyon exspectans Mergl, 1984 coating pebbles in the basal conglomerate of the Trˇenice Formation (Tremadocian) (Mergl 1984, 2009), the oldest proved

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Fig. 1 Geographic position of the locality Lodeˇnice—vinice. a Location of the Prague Basin denudation relic in the Czech Republic and related to the Bohemian Massif (shaded grey). b The Prague Basin relic and schematic structure of its infill. The studied locality is marked. Numbered dots indicate localities mentioned in the text:

1 Zahorˇany, 2 Ha´j Hill, 3 Vra´zˇ, 4 Praha-Motol, 5 Pernı´ka´rˇka, 6 PrahaMichle, 7 Praha-Strasˇnice, 8 Praha-Sˇteˇrboholy. c Detailed topographic situation of the locality surroundings. (a, b modified after Manda 2008 and Chlupa´cˇ 1993)

bryozoans in the Prague Basin come from the volcanoclastic succession in uppermost Klabava Formation (upper Arenigian, Dapingian) (Fig. 2). Marcusodictyon exspectans

was originally described by Mergl (1984) as a ctenostome bryozoan, followed by Havlı´cˇek (1998b), but such assignment was later abandoned, and it has been considered as a

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Trepostome bryozoans from the Zahorˇany Formation

Fig. 2 Stratigraphic division of the Prague Basin infill and position of the Zahorˇany Formation (modified after Kraft et al. 2001; Kraft and Kraft 2003; Bruthansova´ and Kraft 2003)

bryozoan-like problematic fossil (e.g. Taylor 1984; Mergl 2004, 2009; for comment see Xia et al. 2007). Undetermined Marcusodictyon has been reported also from the uppermost Klabava Formation (Mergl 2004). Another colonial organism coating pebbles described from this stratigraphic level is Berenicea vetera Prantl, 1940. It was also originally classified as bryozoan (Prantl 1940, followed by Mergl 1983) but recently considered as bryozoan-like colony (e.g. Mergl 2004). This organism had been earlier identified as an alga Bolopora undosa Lewis, 1926 from the Lower Ordovician (Floian) of North Wales, UK. Bolopora undosa [=Berenicea vetera] may represent a ctenostome bryozoan (Taylor and Ernst 2006). Furthermore, at least three formally undetermined species of trepostome bryozoans, possessing ramose, massive and discoidal colonies, were recognized by Mergl (2004) associated with previously mentioned coating organisms in the uppermost Klabava Formation. The occurrence of bryozoans in the upper Klabava Formation is related to fossil associations enriched mostly with rhynchonelliformean brachiopods, and moderately with gastropods, sponges, hyolithids, ostracodes, conodonts etc. According to Mergl (2004), this is the oldest bryozoan– brachiopod–pelmatozoan (BBP) community. It is a warm climate fauna with Baltic affinities (Fatka and Mergl 2009). In spite of markedly higher diversity in the overlying Sˇa´rka

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and Dobrotiva´ Formations (Oretanian to Dobrotivian regional stages corresponding to Darriwilian to lower Sandbian) (Fig. 2), no bryozoans have been reported. Thus, the Lower to lowermost Upper Ordovician volcano-sedimentary infill of the Prague Basin yields a poor record of undoubted bryozoans concentrated in the single, limited stratigraphic interval inside the Klabava Formation. The number of bryozoans gradually increases in the Berounian Regional Stage (lower Sandbian to lower Katian) (Fig. 2). In the basal Berounian Libenˇ Formation with its alternating sandy and silty to shaly facies, only a very few bryozoan colonies have been found (unpublished data). A similar situation occurs in the overlying, predominantly rhythmic Letna´ Formation as well as the subsequent Vinice Formation, which differs from previous in its predominance of shaly facies. Only one species has been discovered in the Letna´ Formation, and the same number in the Vinice Formation: fenestrate Chasmatoporella havliceki Prantl, 1956 and trepostome Trematopora lamellata Pocˇta, 1902, respectively (Prantl 1956; Pocˇta 1902; Havlı´cˇek and Vaneˇk 1966; Kulich 1984). The richest bryozoan assemblages, typical BBPs of Mergl (2004), occur in two overlying Upper Ordovician units—Zahorˇany and Bohdalec Formations (upper Berounian, probably upper Sandbian to lower Katian) (Fig. 2). The former formation is characterised by siltstones with coarser- or finer-grained intercalations, the latter consisting of dark shales. Carbonate occurs in some sediments of both units. There are carbonate-admixtured or cemented sandy siltstones of the Zahorˇany Formation (Kukal 1960; Havlı´cˇek 1998b), and carbonate-admixtured or cemented silty shales, siltstones and fine-grained sandstones of the Bohdalec Formation (Havlı´cˇek and Fatka 1992; Havlı´cˇek 1998b). Sometimes the carbonate is locally concentrated to form distinct bodies (beds or flat lenses) of silty or sandy carbonates. Bryozoans from those carbonate-rich facies were among the first studied and described from sediments of the Prague Basin, not only because of their high local abundance but also their favourable preservation (Pocˇta 1894). In the Zahorˇany Formation, Pocˇta (1894) initially described a single Ordovician species Ceramopora vadosa Pocˇta, 1894 from Zahorˇany (type locality of the formation) and Vra´zˇ (Fig. 1). Subsequently, using J. Barrande’s collection, Pocˇta (1902) described seven more species: Monticulipora affinis based on material from Zahorˇany and Vra´zˇ, M. certa Pocˇta, 1902 from Zahorˇany, Vra´zˇ and Lodeˇnice; M. crassa Pocˇta, 1902 from Praha-Strasˇnice and Praha-Sˇteˇrboholy (Fig. 1), Trematopora horrida Pocˇta, 1902 from Zahorˇany, ?T. lamellata (ranging from the Vinice Fm.) and ?T. subtilis, both from Zahorˇany, and ?Monotrypa disculus from Zahorˇany and Ha´j Hill (Fig. 1). The most recent revision of this trepostome bryozoan fauna was by Kulich (1984), who confirmed all the species

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described by Pocˇta (1902) with the exception of Monotrypa disculus but without any explanation. Diplopora balabensis Kulich, 1984 was the only new species from the Zahorˇany Formation. To complete the list of the bryozoans from this formation, three other species should be mentioned. They were described from the overlying Bohdalec Formation and subsequently reported also from the Zahorˇany Formation but without any discussion. Havlı´cˇek and Vaneˇk (1966) as well as Kulich (1984) mentioned Monotrypa pragensis Ro¨hlich, 1951 in their lists of species. Information on the occurrences of the following two species in the Zahorˇany Formation is confusing. Trematopora poctai Kettner, 1913 was mentioned by Havlı´cˇek and Vaneˇk (1966), who assigned this species to Batostoma, but it was not mentioned by Kulich (1984), whereas Monotrypa kettneri Prantl, 1941 was listed by Kulich (1984) but not by Havlı´cˇek and Vaneˇk (1966). This problem could not be solved without detailed study of the original material combined with precise locality, stratigraphic and tectonic position. Occurrences of bryozoans in the Zahorˇany Formation are occasionally mentioned in local studies of the Prague Basin (e.g. Zˇelı´zko 1901; Boucˇek 1924; Boucˇek 1928; Hora´k 1957; Havlı´cˇek 1987; Havlı´cˇek and Sˇtorch 1990). On the other hand, bryozoans are absent from the faunal surveys from many other localities. Despite a potential bias of overlooking or ignoring bryozoans, this illustrates their local distribution. Ka´cha and Sˇaricˇ (2009) analysed host and location preferences of epibenthic bryozoans settled on different shells in the Zahorˇany Formation. They identified cystoporates and trepostomes, tentatively assigned to Ceramopora vadosa and Monotrypa disculus, respectively. The overlying Bohdalec Formation yielded even more bryozoan species than the Zahorˇany Formation. They are concentrated in silty shales, siltstones and sandstones, often carbonate enriched or even carbonate dominated. The stratigraphic position of the carbonate-rich layers within the formation is not clear. Havlı´cˇek and Fatka (1992) and Havlı´cˇek (1998b) suggested their situation in the lower and middle parts, whereas Boucˇek (1928) and Havlı´cˇek (1987), supported by Ro¨hlich (1956, 1957, 2006), considered them to be in the upper part. These fossil-rich facies were referred to as the ‘‘Polyteichus horizon’’ or ‘‘Polyteichus facies’’ (Kettner 1916; Boucˇek 1928, respectively; for detailed discussions, see Ro¨hlich and Chlupa´cˇ 1952; Havlı´cˇek 1982) after the typical occurrence of the trepostome bryozoan Polyteichus novaki Perner, 1900. This taxon, as a distinct and common bryozoan, was recognized by Barrande (MS), formally described by Perner (1900), and subsequently studied and revised (Pocˇta 1902; Kettner 1913a, b; Prantl 1932, 1933), and repeatedly mentioned and listed in the Bohdalec Formation fauna (e.g. Ru˚zˇicˇka 1925; Havlı´cˇek and Vaneˇk 1966; Kulich 1984). All other

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bryozoans of the Bohdalec Formation are usually associated with this index species in the Polyteichus biofacies. Therefore, more attention has been paid to the bryozoans of the Polyteichus biofacies than to all other bryozoans, including those from the Zahorˇany Formation. Besides the study of P. novaki, Pocˇta (1902) described three new species: ?Trematopora bifida, Monotrypella glomerata and Holopora foliacea from the Bohdalec Formation in Praha-Michle (Fig. 1), the locality described by Nova´k (1873), where he probably first mentioned an occurrence of Ordovician bryozoans in the Prague Basin. Subsequently, Kettner (1913a, b) studied the bryozoan-rich locality Pernı´ka´rˇka (Fig. 1) in the western part of Prague and reported abundant P. novaki. He also described the following new species: Trematopora poctai, Monotrypa fertilis, Monotrypa radiata, ?Monotrypa circularis, Polyteichus pusillus and Trochopora conica, and listed all of the Ordovician bryozoan localities known at that time. Pouba (1948) established Batostoma prantli from the same stratigraphic level at the nearby locality Praha-Motol (Fig. 1). Occurrences of Monotrypa kettneri Prantl, 1941 and Monotrypa pragensis Ro¨hlich, 1951 in the Bohdalec Formation were discussed above. A similar problem occurs with Monticulipora certa Pocˇta, 1902, reported in the Bohdalec Formation list of fauna by Havlı´cˇek and Vaneˇk (1966) but not by Kulich (1984). Bryozoans from the Kra´lu˚v Dvu˚r Formation (Kra´lodvorian, upper Katian) (Fig. 2) have not previously been reported. This formation is characterised by greenish-grey claystones (Havlı´cˇek 1998b), but a calcareous claystone called the Pernı´k Bed (Brenchley and Sˇtorch 1989) is developed in its uppermost part. Recently, a moderately diverse bryozoan assemblage restricted to that carbonate layer was briefly reported by Mergl (2011a) and subsequently described in detail by Mergl (2011b). He mentioned the occurrence of at least six species but classified only two, Corynotrypa sp. and Graptodictya ?sp., to genus level. Others were only informally characterised morphologically. The Kosov Formation (Kosovian, Hirnantian) (Fig. 2) has a depauperate fauna in response to glaciation. However, bryozoans still occur here, as noted by Marek and Havlı´cˇek (1967) and Krˇ´ızˇ and Steinova´ (2009). In the context of bryozoan occurrences throughout the succession of the Ordovician of the Prague Basin, this paper describes the rich assemblage of well-preserved bryozoans at their diversity peak in the Zahorˇany Formation.

Materials and methods All material described herein was collected from a silty to sandy pelocarbonate flat lens of several meters in lateral extension inside a carbonate-enriched layer at

Trepostome bryozoans from the Zahorˇany Formation

Lodeˇnice—vinice (Fig. 1). This locality is located in Central Bohemia, 22 km WSW of Prague, at the periphery of the Village of Lodeˇnice (Fig. 1). It is situated on the WSW– ENE elongated cuesta called Kneˇzˇ´ı hora. It extends parallel to roads no. 605 and freeway D5 at the south-western edge of the village (GPS 49°590 35.000 N, 14°90 4.500 E). There is a long linear exposure in the topmost part of the dip slope, just between the wooded crest of the cuesta and the highest step of vineyard (vinice in Czech) which extends over the whole dip slope below. The carbonate-rich lens is exposed at the north-easternmost end of the exposure. The section there represents a very thin, some 1.5-m-thick portion of the Zahorˇany Formation (Fig. 2) of the upper Berounian, equivalent of the upper Sandbian and/or lower Katian age. The Lodeˇnice—vinice locality has been investigated since the 19th century. The name has been apparently used as a cumulative for several sites at the cuesta and along its slope foot. However, it can be inferred from geologic situation that all sites are situated near or on the dip slope of the cuesta, and thus belong to the narrow stratigraphic interval within the more than 200-m-thick Zahorˇany Formation at the Lodeˇnice area, and are of similar age. The studied site is one of the few places in the Prague Basin where bryozoans represent a dominant (or at least one of the dominant) components of the assemblage. In addition, they are favourably preserved in fragments as well as complete large colonies which are common or even predominate. The accompanying fauna is represented mainly by disarticulated trilobites (head shields and pygidia of Dalmanitina proeva predominate, trinucleid Marrolithus ornatus less frequently), rhynchonelliformean brachiopods and large conulariids. Linguliformean brachiopods, gastropods and graptolites are less common. Out of the pelocarbonate lens, the amount of carbonate decreases and fossils disappear. Some 20 m SE from the pelocarbonate exposure, a section was measured and an ichnological analysis was done by Bokr et al. (personal communication). In spite of the short distance between these sites, correlation was difficult due to lateral variations in thicknesses of the individual layers combined with poor outcrop exposure in critical areas. However, the pelocarbonate lens is considered to be a continuation of the finegrained micaceous, carbonaceous sandstone situated roughly at the base of the upper half of the measured section. Ichnofossils from the exposure SW of the site studied herein were also described by Mikula´sˇ (1990), and a comment on them in the wider palaeontological framework was published by Mikula´sˇ (1999). The locality is interpreted as situated close to a palaeobathymetric high (Havlı´cˇek 1998b). Such zones, indicating shallower-water conditions in comparison with other parts of the Prague Basin, are indicated not only by

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ichnological markers (Mikula´sˇ 1999) but also by a Drabovia latior Community fossil assemblage (Havlı´cˇek 1982; Havlı´cˇek and Vaneˇk 1990; Havlı´cˇek and Fatka 1992; Havlı´cˇek 1998b) with its abundant brachiopods, trilobites, echinoderms and others (Havlı´cˇek 1998b) in contrast to the deeper-water Aegiromena aquila–Marrolithus ornatus Community (Havlı´cˇek and Fatka 1992; Havlı´cˇek 1998b), characterised by lower diversity and predominance of molluscs, brachiopods and uncommon trilobites (Havlı´cˇek1998b). Bryozoans were investigated in thin sections using a binocular transmitted-light microscope. Morphologic character terminology is modified from Anstey and Perry (1970). The following morphologic characters were measured and used for discriminating species in the studied material (Fig. 3): Branch diameter, exo- (endo-)zone width, autozooecial aperture width (non-macular and macular), autozooecial aperture spacing (non-macular and macular), acanthostyle diameter, mesozooecia width, mesozooecial diaphragm spacing, number of mesozooecia and acanthostyles surrounding each autozooecial aperture, wall thickness in exozone, axial zooecia width. The spacing of structures is measured as the distance between nearest centres. Statistics were summarized using arithmetic mean, sample standard deviation, coefficient of variation, and minimum and maximum values. Repository Studied material is housed at the National Museum in Prague, under numbers L42169 to L42214. Systematic palaeontology Phylum Bryozoa Ehrenberg, 1831 Class Stenolaemata Borg, 1926 Order Trepostomata Ulrich, 1882 Family Trematoporidae Miller, 1889 Genus Trematopora Hall, 1852 Type species T. tuberculosa Hall, 1852; Lower Silurian (Niagaran); North America. Diagnosis Ramose colonies, often originating from encrusting base. Autozooecial apertures oval to rounded with peristomes. Diaphragms usually rare, often absent in endozone. Abundant mesozooecia with abundant diaphragms, thin-walled and beaded in initial parts of exozone, near colony surface becoming thick-walled. Mesozooecial apertures often completely covered by laminated skeleton. Acanthostyles abundant. Walls thin in endozone, thickened in peripheral parts of exozone displaying obliquely laminated microstructure. Remarks Trematopora Hall, 1852 differs from Batostoma Ulrich, 1882 by having oval to rounded autozooecial

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apertures and abundant mesozooecia covered with skeletal material, from Eridotrypa Ulrich, 1893 by having autozooecia that bend sharply in exozone, possess rounded apertures arranged irregularly on the colony surface, as well as by abundant acanthostyles. Occurrence

Ordovician to Silurian, worldwide.

Trematopora bifida Pocˇta, 1902; Figs. 4a–f, 5a–f; Table 1 v1902

?Trematopora bifida Pocˇta, p. 315, pl. 96, fig. 7.

Material

L42172–L42174, L42175–L42180.

Description Ramose branched colonies, branch diameter 5.00–7.40 mm. Exozone distinct, 0.66-1.80 mm wide, endozone 2.40–5.40 mm wide. Autozooecia long, polygonal in cross section in endozone, bending sharply in exozone. Autozooecial apertures rounded to slightly angular. Autozooecial diaphragms rare, thin. Mesozooecia abundant,

Fig. 3 Measured morphologic characters: branch diameter (WB), exozone (ExW) and endozone (EndW) width, autozooecial aperture width (AW), autozooecial aperture spacing (ADB), acanthostyle

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originating at base of exozone, beaded in places of development of diaphragms, 3–7 surrounding each autozooecial aperture. Diaphragms in mesozooecia straight, 5–6 spaced per 1 mm of mesozooecial length. Acanthostyles large, prominent, having distinct hyaline cores, 3–7 surrounding each autozooecial aperture. Autozooecial walls 0.005– 0.010 mm thick, granular-prismatic in endozone; showing reverse V-shaped lamination, integrated with locally visible dark border between zooecia, locally monilae-shaped thickened, 0.04–0.10 mm thick in exozone. Remarks Trematopora bifida Pocˇta, 1902 differs from T. clariondi Termier and Termier, 1950 from the Katian of Morocco in having smaller autozooecial apertures (aperture width 0.10–0.20 versus 0.14–0.30 mm in T. clariondi), and from T. cumingsi Troedsson, 1929 from the Katian of Greenland in smaller autozooecial apertures (aperture width 0.10–0.20 versus 0.14–0.30 mm in T. cumingsi). Trematopora bifida differs from

diameter (AcD), mesozooecial diameter (MD), mesozooecial diaphragm spacing (MDSp), exozonal wall thickness (EWT)

Trepostome bryozoans from the Zahorˇany Formation

Fig. 4 Trematopora bifida Pocˇta, 1902. a Transverse sections of branches, L42172. b Oblique branch section, L42175. c Oblique branch section, L42179. d Longitudinal section of exozone, L42175.

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e Tangential section showing autozooecial apertures, acanthostyles and mesozooecia, L42175. f Tangential section showing autozooecial apertures, acanthostyles and mesozooecia, L42175

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Fig. 5 a–f Trematopora bifida Pocˇta, 1902. a–c Branch transverse section showing autozooecial chambers in endozone and exozone and beaded mesozooecia, L42172. d Tangential section showing autozooecial apertures, acanthostyles and mesozooecia, L42177.

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e, f Longitudinal section of exozone showing beaded mesozooecia, L42177. g, h Lodenicella lamellata (Pocˇta, 1902), transverse zoarial sections showing encrusting parts with arising branched parts (g L42184, h L42189)

Trepostome bryozoans from the Zahorˇany Formation

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Table 1 Morphometric summary statistics of Trematopora bifida Pocˇta, 1902 N

X

SD

CV

Min

Max

Branch diameter (mm)

12

6.17

0.85

13.78

5.00

7.40

Exozone width (mm)

12

0.90

0.44

49.15

0.32

1.80

Endozone width (mm)

12

4.38

1.07

24.53

2.40

5.80

Autozooecial aperture width (mm)

30

0.14

0.02

16.83

0.10

0.20

Autozooecial aperture spacing (mm)

30

0.24

0.03

14.64

0.18

0.32

Acanthostyle diameter (mm)

30

0.07

0.01

18.38

0.04

0.09

Mesozooecial width (mm)

30

0.06

0.022

36.35

0.03

0.11

Acanthostyles per aperture

30

5.1

1.125

22.06

3.0

7.0

Mesozooecia per autozooecial aperture

30

3.2

1.031

32.21

1.0

6.0

Mesozooecial diaphragm spacing (mm)

30

0.14

0.029

21.01

0.10

0.20

Autozooecial wall thickness in exozone (mm)

30

0.07

0.015

19.89

0.04

0.10

N number of measurements, X mean, SD standard deviation, CV coefficient of variation, Min minimum value, Max maximum value

T. tuberculosa Hall, 1852 from the Katian of France and Silurian of North America in having larger acanthostyles and larger apertures (average acanthostyle diameter 0.07 mm versus 0.04 mm in T. tuberculosa; average aperture width 0.14 versus 0.12 mm in T. tuberculosa; measurements for T. tuberculosa from Ernst and Key, 2007). Occurrence Zahorˇany Formation, Upper Ordovician, Katian; Lodeˇnice—vinice, Prague Basin, Czech Republic. The historical source of Pocˇta (1902) mentioned this species from the locality which had yielded fauna typical for the Bohdalec Formation (see above). Thus, its discovery at Lodeˇnice—vinice proved its longer range and the earliest occurrence in the Prague Basin. Genus Lodenicella gen. nov. Derivation of name locality Lodeˇnice.

The genus name refers to the type

Type species ?Trematopora lamellata Pocˇta, 1902 [=Trematopora? subtilis Pocˇta, 1902]. Zahorˇany Formation, Upper Ordovician, upper Sandbian—Katian; Lodeˇnice— vinice, Prague Basin, Czech Republic. Diagnosis Initially encrusting colonies producing ramose branched parts. Autozooecia long, oriented for long distance parallel to substrate or branch axis, curved slightly in the outermost endozone with sharp bend in exozone, polygonal and having larger diameter in endozone, semicircular to trapezoid at the base in encrusting parts. Autozooecia growing from thin epitheca in encrusting parts. Branched parts with narrow exozone, circular or elliptical in transverse section, with a distinct bundle of larger axial zooecia. Autozooecial apertures polygonal. Basal diaphragms lacking to common, occurring in the transition between endo- and exozone, lacking in endozone.

Mesozooecia rare to common, short. Acanthostyles common to abundant, having distinct hyaline cores and laminated sheaths, sometimes absent. Locally large massive styles developed. Autozooecial walls in exozone thickened, having obliquely laminated microstructure with serrated zooecial boundaries. Remarks Lodenicella gen. nov. develops colonies consisting of extended encrusting parts from which long branched projections arise. Such a pattern is usual in many stenolaemate bryozoans. An encrusting part of Lodenicella shows similarity with Heterotrypa Nicholson, 1879, but differs from it in having few diaphragms and in exozonal walls with serrated zooecial boundaries. Branched parts display strong resemblance with Eridotrypa Ulrich, 1893, especially in having narrow exozone, larger zooecial diameters in the axial part of branches and serrated walls in exozone. However, Eridotrypa does not have large and distinct acanthostyles, and it possesses occasionally diaphragms in endozone. Ross (1967) and Astrova (1978) stressed the absence of real acanthostyles (styles with hyaline core and laminated sheath). Instead, small needle-like styles are present. The new genus is also similar to the genus Lamottopora Ross, 1963, but differs in having short open mesozooecia with thin diaphragms instead of large sealed mesozooecia with thick cystoidal diaphragms of Lamottopora. Ross (1967) placed the genus Eridotrypa alongside her own genera Lamottopora Ross, 1963 and Newportopora Ross, 1967, in the family Aisenvergiidae Dunaeva, 1964. She argued that these genera have a similar budding pattern with long zooecia having larger diameters in the axial part. The family Aisenvergiidae contained originally three genera: Aisenvergia Dunaeva, 1964, Volnovachia Dunaeva, 1964 and Polycylindricus Boardman, 1960. However, these genera are characterised by completely different wall structure (predominantly merged, without visible zooecial boundaries), and presence of exilazooecia instead of

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mesozooecia. Therefore, Astrova (1978) criticized the placement of Eridotrypa, Lamottopora and Newportopora in the family Aisenvergiidae. She placed Eridotrypa in the family Trematoporidae, which appears justified because Eridotrypa and Trematopora share serrated wall structure and endozonal zooecial diameters larger than those in

A. Ernst et al.

exozone. This opinion is also followed in the present paper. Lodenicella gen. nov. is placed herewith in the family Trematoporidae because of serrated walls, presence of mesozooecia and acanthostyles. Lodenicella lamellata (Pocˇta, 1902); Figs. 5g, h, 6a–f, 7a–i, 8a–d; Table 2

Fig. 6 Lodenicella lamellata (Pocˇta, 1902). a, b Transverse section of encrusting colony, L42184. c, d Longitudinal section of encrusting colony, L42188. e, f Tangential section of encrusting colony, showing autozooecial apertures and acanthostyles, L42188

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Trepostome bryozoans from the Zahorˇany Formation

Fig. 7 Lodenicella lamellata (Pocˇta, 1902). a Longitudinal and transverse sections of branched colonies, L42193. b Oblique and longitudinal section through branched and encrusting parts, L42187. c Place of origination of branched part from the encrusting base, L42189. d, e Branch transverse section, showing narrow exozone and

21

axial bundle of zooecia, L42194. f Branch transverse section showing serrated autozooecial wall boundary in exozone, L42196. g, h Branch longitudinal section, L42193. i Branch longitudinal section showing mesozooecium, L42191

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22

Fig. 8 Lodenicella lamellata (Pocˇta, 1902). a–e Tangential section showing autozooecial apertures, mesozooecia and acanthostyles, L42192. c, d Branch transverse section showing massive acanthostyles, L42206. Trepostomata sp. indet, L42214. e Branch oblique

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A. Ernst et al.

section. f Longitudinal section of exozone. g Longitudinal section showing wall structure in exozone. h Tangential section showing autozooecial apertures and mesozooecia

Trepostome bryozoans from the Zahorˇany Formation

23

Table 2 Morphometric summary statistics of Lodenicella lamellata (Pocˇta, 1902) N

X

SD

CV

Min

Max

Colony sheet thickness (mm)

10

0.84

0.213

25.347

0.54

1.21

Branch diameter (mm)

22

2.14

0.569

26.603

1.26

3.60

Exozone width (mm)

22

0.28

0.050

18.184

0.20

0.38

Endozone width (mm)

22

1.59

0.554

34.935

0.69

3.08

Autozooecial aperture width (mm)

55

0.19

0.028

14.891

0.12

0.26

Autozooecial aperture spacing (mm)

55

0.25

0.042

16.509

0.16

0.42

Autozooecial aperture width macular (mm)

12

0.27

0.038

13.807

0.24

0.37

Autozooecial aperture spacing macular (mm)

10

0.36

0.034

9.357

0.31

0.42

Larger acanthostyle diameter (mm)

25

0.078

0.020

25.841

0.050

0.125

Smaller acanthostyle diameter (mm)

55

0.039

0.010

24.535

0.020

0.060

Mesozooecial width (mm) Autozooecial wall thickness in exozone (mm)

30 40

0.052 0.049

0.023 0.014

44.717 27.847

0.025 0.025

0.120 0.085

Axial zooecial width (mm)

20

0.27

0.044

16.359

0.20

0.36

N number of measurements, X mean, SD standard deviation, CV coefficient of variation, Min minimum value, Max maximum value Table 3 Morphometric summary statistics of Trepostomata sp. indet N

X

SD

CV

Min

Max

Autozooecial aperture width (mm)

20

0.16

0.024

15.36

0.11

0.2

Autozooecial aperture spacing (mm)

20

0.21

0.029

13.65

0.18

0.26

Mesozooecia width (mm)

20

0.06

0.019

33.82

0.03

0.11

Mesozooecia per autozooecial aperture

10

4.5

0.850

18.89

3.0

6.0

Autozooecial wall thickness in exozone (mm)

10

0.04

0.015

37.00

0.03

0.08

N number of measurements, X mean, SD standard deviation, CV coefficient of variation, Min minimum value, Max maximum value

v1902 v1902 Material

?Trematopora lamellata Pocˇta, p. 315–316, pl. 96, figs. 1–3. ?Trematopora subtilis Pocˇta, p. 316, pl. 96, fig. 6. L42169–L42171, L42173–L42214.

Description Initially encrusting colonies producing ramose branched parts. Encrusting colonies usually in form of hollow tubes developed as encrusting an unpreserved cylindrical substrate (algae?). Colonial sheets 0.54–1.21 mm thick. Ramose branches 1.26–3.60 mm in diameter, with 0.20–0.38 mm wide exozones and 0.69–3.08 mm wide endozones. Autozooecia long, oriented for long distance parallel to substrate or branch axis, curved slightly in the outermost endozone with sharp bend in exozone, polygonal and having larger diameter in endozone, oval to rounded-polygonal in exozone. Axial bundle of larger zooecia in branched colonies distinct. Autozooecial diaphragms absent in endozone and in outermost parts of zooecia, occurring mainly in transition between endozone and exozone, straight, thin. Mesozooecia rare, locally common, small, short, rounded-polygonal, spaced usually at junctions between autozooecia, bearing closely spaced diaphragms. Acanthostyles common to

abundant, usually 3–5 surrounding each aperture, small to moderate in size, having narrow hyaline cores and wide laminated sheaths, restricted to exozone, sometimes lacking. Locally acanthostyles of two types developed: 2–4 larger acanthostyles surrounding each aperture and 1–2 smaller acanthostyles between the larger ones (Fig. 6e, f). Autozooecial walls in endozone having indistinct lamination, 0.005–0.010 mm thick, locally crenulated. Autozooecial walls in exozone displaying serrated dark border between autozooecia and distinct reverse V-shaped lamination, 0.025–0.085 mm thick. Maculae consisting of larger zooecia, 1.35–1.70 mm in diameter. Remarks Branched parts of Lodenicella lamellata (Pocˇta, 1902) differ from the encrusting ones in slightly elongated autozooecial apertures and thicker walls in exozone. The latter character is apparently an adaptation to the ramose mode of growth, permitting more colony stability. Occurrence Zahorˇany Formation, Upper Ordovician, Katian; Lodeˇnice—vinice, Prague Basin, Czech Republic. Family uncertain Trepostomata gen. et sp. indet.; Fig. 8e–h; Table 3

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24

Material L42214.

A. Ernst et al.

Two fragments of a single colony, L42212,

Description Branched colony, 2.9 mm in diameter, with 0.75 mm wide exozone and 1.4 mm wide endozone. Autozooecia moderately long, oriented for a short distance parallel to branch axis, curved with sharp bend in exozone, polygonal to rounded-polygonal in endozone. Autozooecial apertures polygonal. Autozooecial diaphragms absent. Mesozooecia abundant, small to moderately large, originating in early exozone, rounded-polygonal, situated at junctions between autozooecia, bearing few diaphragms. Acanthostyles absent. Autozooecial walls in endozone having indistinct lamination, 0.005–0.010 mm thick. Autozooecial walls in exozone irregularly thickened, showing coarse reverse V-shaped lamination, without autozooecial boundaries, 0.03–0.08 mm thick. Maculae not observed. Remarks As far as this material is represented by a single colony, it is not sufficient to identify this species, genus, or even family. It shows distant similarity to Hallopora Bassler, 1911, but differs by having fewer diaphragms in mesozooecia and lacking autozooecial diaphragms, as well as in polygonal apertures instead of rounded ones in Hallopora. Occurrence Zahorˇany Formation, Upper Ordovician, Katian; Lodeˇnice—vinice, Prague Basin, Czech Republic.

Discussion The studied bryozoan fauna mainly contains ramose branched trepostome colony forms. Lodenicella gen. nov. develops colonies consisting of extended encrusting parts from which long branched projections arise. The encrusting parts of this bryozoan often exhibit a tubular shape, which implies the presence of non-mineralized cylindrical substrate which decayed after its death. Bryozoans show no visible traces of post-mortem transportation, as most colonies are complete and long acanthostyles not broken (Figs. 4a, 5g, h, 7a, b, 8c, d). The sediments of the Zahorˇany Formation at Lodeˇnice— vinice are interpreted as having formed under shallow-water conditions (Havlı´cˇek 1998b; Mikula´sˇ 1999). The matrix of the embedding limestones contains abundant, very wellsorted quartz grains (e.g. Figs. 4a, 5a, b, g, h, 6e, f). This suggests a nearshore and at least moderate water energy environment. The tubular colonies of Lodenicella gen. nov. are also ramose as they encrust ramose cylindrical substrates. No bryozoans encrusting the bottom substrate itself were observed in the studied material. High and consistent sedimentation rates represent a threat for suspension feeding

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animals such as bryozoans (e.g. Spjeldnaes 1996), so they may have responded by producing ramose colonies. Ramose colonies have another advantage, namely expansion into the water column resulting in more surface area for filtering water (McKinney and Jackson 1989, p. 76). The local development of massive acanthostyles in Lodenicella gen. nov. is interpreted as a reaction to occasional predation (Figs. 6b–f, 8c, d). Many bryozoans (as well as other animals affected by biting predators) develop spinelike structures for defence. Not all parts of colonies of Lodenicella lamellata (Pocˇta, 1902) contain large acanthostyles; in some parts (sometimes in the same colony) acanthostyles are lacking (compare Fig. 8a, b). This implies that this bryozoan was able to develop defensive structures in response to predator attacks, as observed in modern bryozoans (Yoshioka 1982; Harvell 1984). Trematopora bifida Pocˇta, 1902 is also equipped with prominent acanthostyles which are herein interpreted as defensive structures (Fig. 5b, d). Acknowledgments We are grateful to P. Bokr for providing data from the measured section at Lodeˇnice—vinice and help with correlation of the section and the fossil site. Financial support for this research was provided by the Ministry of Education, Youth and Sports of the Czech Republic through Research Plans No. MSM0021620855 (to Petr Kraft) and project NAKI of MKCˇR number DF12P01OVV021 (to Kamil Za´gorsˇek). Caroline Buttler, Cardiff, and Marcus Key, Carlisle, are thanked for their helpful and constructive reviews.

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