Bryozoans of the Latorp and Volkhov horizons (Lower-Middle ...

ISSN 00310301, Paleontological Journal, 2011, Vol. 45, No. 8, pp. 887–980. © Pleiades Publishing, Ltd., 2011.

Bryozoans of the Latorp and Volkhov Horizons (Lower–Middle Ordovician) of the Leningrad Region A. V. Koromyslova Borissiak Paleontological Institute of the Russian Academy of Sciences Received April 15, 2009; in final form, December 7, 2009

Abstract—This monograph deals with the morphology of bryozoans of the orders Cystoporida and Trepos tomida from the Latorp and Volkhov horizons (Lower–Middle Ordovician, Floian–Darriwilian stages) of the Leningrad Region. Diagnoses of some families belonging to these orders are revised. Based on morphological features of the bryozoans studied and on the succession of their taxa, four assemblages and three stages in their development are established. In addition, the stratigraphic and paleogeographic distributional patterns of bryozoans in the Lower and Middle Ordovician of the world are analyzed. DOI: 10.1134/S0031030111080028

TABLE OF CONTENTS INTRODUCTION CHAPTER 1. History of Studying Bryozoans in the Latorp and Volkhov Horizons of the Leningrad Region CHAPTER 2. Morphology of Skeletal Elements in the Colonies of the Oldest Bryozoans 2.1. Types and shapes of colonies 2.2. Internal structure of bryozoan colonies 2.2.1. Body plan of colonies and budding patterns of autozooecia 2.2.2. Autozooecia and their apertures 2.2.3. Polymorphism of zooecia 2.2.4. Vesicular tissue 2.2.5. Intrazooecial structures CHAPTER 3. Systematic Paleontology Phylum Bryozoa Ehrenberg, 1831 Class Stenolaemata Borg, 1926 Order Cystoporida Astrova, 1964 Suborder Ceramoporina Bassler, 1913 Family Revalotrypidae Gorjunova, 1986 Genus Revalotrypa Bassler, 1952 Revalotrypa krestensis Koromyslova in Gorjunova et Koromyslova, 2008 Revalotrypa gibbosa Bassler, 1911 Revalotrypa papillaris (Modzalevskaya, 1953) Genus Lynnopora Gorjunova et Koromyslova, 2008 Lynnopora lunata Gorjunova et Koromyslova, 2008 Order Trepostomida Ulrich, 1822 Suborder Esthonioporina Astrova, 1978

Family Esthonioporidae Vinnassa de Regny, 1921 Genus Esthoniopora Bassler, 1911 Esthoniopora clara Koromyslova, sp. nov. Esthoniopora lessnikowae (Modzalevskaya, 1953) Esthoniopora curvata Bassler, 1911 Genus Esthonioporella Modzalevskaya, 1953 Esthonioporella miranda Koromyslova, sp. nov. Family Aisenvergiidae Dunaeva, 1964 Subfamily Orbiporinae Astrova, 1978 Genus Orbipora Eichwald, 1856 Orbipora acanthophora Bassler, 1911 Suborder Halloporina Astrova, 1965 Family Halloporidae Bassler, 1911 Genus Dianulites Eichwald, 1829 Dianulites fastigiatus Eichwald, 1829 Dianulites janischevskyi Modzalevskaya, 1953 Genus Diplotrypa Nicholson, 1879 Diplotrypa petropolitana Nicholson, 1879 Diplotrypa olgae Koromyslova, 2004 Diplotrypa moniliformis Bassler, 1911 Family Phragmoporidae Pushkin, 1987 Genus Phragmopora Vinassa de Regny, 1921 Phragmopora lavaensis Pushkin, 1999 in Pushkin et Popov, 1999 Phragmopora multiporata (Bassler, 1911) Family Monticuliporidae Nicholson, 1881 Subfamily Dittoporinae Vinassa de Regny, 1921

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Genus Dittopora Dybowski, 1877 Dittopora clavaeformis Dybowski, 1877 Dittopora annulata (Eichwald, 1860) Suborder Amplexoporina Astrova, 1965 Family Stenoporidae Waagen et Wentzel, 1886 Subfamily Amplexoporinae Miller, 1889 Genus Anaphragma Ulrich et Bassler, 1904 Anaphragma verectum Koromyslova, sp. nov. CHAPTER 4. Bryozoan Assemblages in the Latorp and Volkhov Horizons of the Leningrad Region CHAPTER 5. Stages in the Development of the Latorp–Volkhov Bryozoans CHAPTER 6. Distribution of the Oldest Bryozoans in Time and Space 6.1. Stratigraphic distribution of the oldest bryozoans in various regions of the world 6.2. Geographic distribution of the oldest bryozoans CONCLUSIONS REFERENCES

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INTRODUCTION To date the bryozoan assemblage of the Latorp horizon (Lower Ordovician, Floian Stage) in the Len ingrad Region is the oldest within the East European Platform. It is represented by one genus and three spe cies of the order Cystoporida and six genera and ten species of the order Trepostomida. In the Early Ordov ician and at the beginning of the Middle Ordovician, the environmental conditions in the Baltic Sea basin were the most favorable in comparison with the other coeval basins, thus facilitating the considerable increase in the diversity of bryozoans. From the mid dle Volkhov time onward (Middle Ordovician, Dapin gian Age) bryozoans were represented by as many as four orders (Cystoporida, Trepostomida, Tubulipor ida, and Cryptostomida) and comprised about 30 spe cies. The rare bryozoans of Latorp, as well as their great numbers and diversity in Volkhov, provide unique material for studying the initial stage in the develop ment of the phylum Bryozoa. In addition, the descrip tion of this assemblage, which is one of the most ancient on the Earth, is important for the solution of the problem about the time and place of origin of bry ozoans. Despite there are many publications on Ordovician bryozoans (Modzalevskaya, 1953, 1986; Gorjunova and Lavrentjeva, 1987; Gorjunova, 1988, 1992, 1996; Taylor and Rozhnov, 1996; Pushkin and Popov, 1999, 2005), many of these problems remain still unsolved. In this work the author aims to refine the morphol ogy of the bryozoan genera and species of the Latorp and Volkhov horizons, to reveal their assemblages and stages in their development, to study the stratigraphic and geographic distribution of bryozoans in the Trem

adocian–Early Darriwilian, and to refine the time and place of origin of the main bryozoan orders of the class Stenolaemata. This work uses the recently accepted international stratigraphic scale, regional scheme of Baltoscandia, and local stratigraphic scheme of the Leningrad Region (Fig. 1). The Latorp horizon was established by V. Jaanus son in 1960 (Männil, 1966) and was authorized by the Resolutions of Interdepartmental Stratigraphical Conference (Resolutions …, 1987). This horizon is divided into the lower (Hunneberg) and upper (Bill ingen) subhorizons, which are frequently raised to the rank of separate horizons (Resolutions …, 1987; Fedorov, 2003, 2004), whereas the Latorp horizon is considered as a superhorizon that in addition to the Hunneberg and Billingen horizons includes the Varanguan horizon (Dronov, 2000; Koren et al., 2006; Ershova and Fedorov, 2006). The boundary between the Hunneberg and Billingen subhorizons (horizons) is poorly defined on the territory of Baltoscandia, since there are no considerable changes in faunal assemblages, or changes in depositional pattern, etc. (Ershova and Fedorov, 2006; Ershova, 2008). Thus, these two subhorizons (horizons) are discussed in this paper as a single stratigraphic interval: Latorp horizon. The lower Latorp horizon belongs to the Tremadocian Stage of the International Stratigraphic Scale (ISS) and General Stratigraphic Scale (GSS), its main part belongs to the Floian Stage of the Interdepartmental Stratigraphic Scale or to the Arenigian Stage (GSS) (Koren et al., 2006; Ershova, 2008; International Stratigraphic Committee (ISC), 2008). According to the Resolutions of the Interdepartmental Regional Stratigraphical Conference (Resolutions …, 1987), the Latorp horizon is represented by the Leetse Forma tion, which includes the upper part of the Glauconitic Sand and the base of the Glauconitic Limestone (=lower part of the Dikari Limestone) (Dronov, 1998; Ershova, 2008). It is believed that the names “Volkhov horizon” and “Volkhov Formation” were given by the American geologist P. Raymond, who visited Russia in 1916 (Geological Dictionary, 1955). The Volkhov horizon is represented by the Volkhov Formation, which is divided into the lower, middle, and upper subforma tions, which retain their conventional names: Dikari, Zheltyaki, and Frizy, respectively. The lower and mid dle subformations correspond to the Dapingian Stage of the Interdepartmental Stratigraphic Scale, the upper subformation corresponds to the Lower Darri wilian of the Interdepartmental Stratigraphic Scale. The Dapingian Stage and the lower Darriwilian corre spond to the Arenigian Stage of GSS. The boundary between the Latorp and Volkhov horizons (between the Lower and Middle Series of the Ordovician, respectively) runs within the “Dikari” Limestone and coincides with the surface that is called “Steklo” in Russia (Dronov, 2000). “Steklo” is a “hard ground” PALEONTOLOGICAL JOURNAL

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BRYOZOANS OF THE LATORP AND VOLKHOV HORIZONS

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with amphorashaped burrows of boring organisms Gastrohaenolites oelandicus (Dronov et al., 1993; Dronov, 1998, 2000, 2004). The material for the work is a bryozoan collection comprising more than 500 colonies or their fragments from seven sections of five localities in the Leningrad Region (Fig. 2). In August 2005 the author in cooper ation with P.V. Fedorov and V.B. Ershova, members of the Chair of Dynamic and Historical Geology, Geo logical Department, St. Petersburg State University collected 37 bryozoan specimens from the Latorp horizon near the village of Belye Kresty. In the mid 1980s and in 2000 members of the Paleontological Institute of the Russian Academy of Sciences during the expeditions headed by S.V. Rozhnov collected bry ozoans from the Latorp and Volkhov horizons in the vicinity of the village of Putilovo and on the Lava, Volkhov, and Lynna rivers. The material from the sec tions of Putilovo and the Lava and Volkhov rivers was granted to the author for studying by R.V. Gorjunova (31 specimens, part of which was preliminarily deter mined and published in Gorjunova’s papers (1987, 1996)) and by A.A. Madison (about 440 specimens) from the section of on the Lynna River. This collection also contains 35 bryozoan colonies collected by the author on the Lynna River in 2002. It is worth noting that the colonies passed by Madison were collected from the section of on the Lynna River by washing rock samples from 15 levels (Fig. 3). The washing yielded “residues,” which contained many brachio pods, ostracodes, and bryozoans, which for the sake of convenience were divided into fractions 10–5, 5–2, and 20% occurrences of colonies), Revalotrypa eugeniae (>10%), Phragmopora lavaensis (>10%), Hemi phragma priscum (>10%), and Dittopora clavaeformis (5–10%); 8 This

species was placed in the genus Hemiphragma; however, it cannot be identified because of poor preservation. PALEONTOLOGICAL JOURNAL

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(II) less numerous, Revalotrypa krestensis (2–5%), Esthonioporella miranda (2–5%), and Dianulites hele nae (2–5%); 9

(III) isolated, Revalotrypa gibbosa (1–2%), Estho niopora clara (1–2%), Esthoniopora curvata (=E. cli vosa) (1–2%); Hemiphragma sp. (1–2%), and Dit topora annulata (1–2%). In deposits of the Latorp of the Leningrad Region the genera Revalotrypa, Esthoniopora, Esthonioporella, Dianulites, Phragmopora, Dittopora, and Hemi phragma are recorded for the first time. Of these, the genus Dianulites, and, therefore, the family Hal loporidae and the suborder Halloporina, are known from the Floian Stage of western Utah (United States) (upper part of the Fillmore Formation) (see Chapter 6 for details). In addition, the genus Revalotrypa belongs to the suborder Ceramoporina (family Revalotrypi dae), and the genera Esthoniopora and Esthonioporella belong to the suborder Esthonioporina (family Estho nioporidae), representatives of which are also known from deposits that are older than those of the Latorp horizon. Thus, the first occurrence of the suborder Esthonioporina (family Aisenvergiidae) has been recorded in the Tremadocian of the province of Hubei in China (Fenxiang Formation, Paltodus deltifer con odont Zone), and that of ?Ceramoporina (family Cer amoporidae) has been recorded in the Tremadocian?– Floian of Oklahoma, the United States (Kindblade Formation, Arbuckle Group, Canadian Stage) (see Chapter 6 for details). Thus, in the Latorp of the Leningrad Region the most representative are bryozoans of the genera Estho niopora and Revalotrypa. Here the first occurrences of 13 species, seven genera, five families, three suborder, and two order have been recorded. At the boundary between the Latorp and Volkhov horizons, or the Lower and Middle Ordovician (Floian and Dapingian stages) disappeared five species bryo zoan. Assemblage II, Lower Volkhov (Dapingian Stage) (Fig. 20). This assemblage includes bryozoans of the orders Cystoporida and Trepostomida. The order Cys toporida is represented by one genus Revalotrypa with three species, two of which are known from the Latorp time onward (R. krestensis and R. gibbosa) and one, R. papillaris, is known from the Early Volkhov onward. The order Trepostomida is characterized by 16 species 9 E.A.

Modzalevskaya (1951, 1953) was the only researcher who revealed bryozoans Revalotrypa gibbosa in the Latorp horizon. Her dissertation is the only paper in which this species have been described from these deposits.

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of seven genera: Esthonioporella with one species and Dittopora with two species, known from the Latorp time onward; Esthoniopora with three species, two of which (E. lessnikowae and E. curvata) are known from the Latorp time onward and one, E. communis, from the Early Volkhov onward; Dianulites with seven spe cies, one of which is known from the Latorp time onward and six—D. fastigiatus, D. modzalevskae, D. multimesoporicus, D. eichwaldi, D. collucatus, and D. janischevskyi—are known from the Early Volkhov onward. The species of the genera Diplotrypa (D. pet ropolitana), Phragmopora (Ph. multiporata), and Ana phragma (A. vetustum) appeared in the Early Volkhov time. In deposits of the Lower Volkhov the first occur rences of nine new species of the earlier existed genera belonging to the orders Cystoporida and Trepostomida as well as two species of two new genera, Diplotrypa and Anaphragma, have been recorded. Both of these genera belong to the order Trepostomida. Diplotrypa belongs to the previously known family Halloporidae, and Anaphragma is a representative of the new family Stenoporidae of the suborder Amplexoporina. The Lower Volkhov subhorizon of the Leningrad Region has yielded 19 species of eight genera, of which bryozoans of the genera Dianulites, Diplotrypa, and Anaphragma and, to a lesser degree, Revalotrypa and Esthoniopora predominated. At this time the first occurrences of 11 species, two genera, one family, and one suborder have been recorded. However it is worth noting that the Early Volkhov age of these bryozoans remains open to question, since at present the boundary between the Latorp and Volkhov horizons is drawn along the surface of “hard bottom,” located within the “Dikari” limestone (Dronov et al., 1993; Dronov, 1998, 2000, 2004). Pre viously this limestone member entirely belonged to the Volkhov horizon (Subhorizon BIIα), and it is unknown from which part of “Dikari” limestone come the bry ozoans of the lower Volkhov horizon that were described in the literature. If they were described from the lower part, i.e., from below the surface of “Steklo,” they should be assigned to the Latorp horizon. Unfor tunately, the author did not collected bryozoans from this part of the Volkhov horizon, and the available bry ozoan collections have no indications as to the part of “Dikari” limestone from which they were collected. At the boundary between the lower Volkhov and Middle Volkhov horizons no disappearances of bryo zoan species have been recorded.

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Assemblage III, Middle Volkhov (Dapingian Stage) (Fig. 20). In the Middle Volkhov bryozoans of the orders Cystoporida and Trepostomida persisted; there also appeared representatives of two new orders, Tubu liporida and Cryptostomida. The order Cystoporida was, as before, represented by the only genus Revalot rypa with three species, two of which are known from the Latorp time onward and one species, from the Early Volkhov time onward. The bryozoans of the order Trepostomida are represented by 24 species of 12 genera: Esthonioporella with one species, known from the Latorp time onward; Esthoniopora with three species, two of which are known from the Latorp time onward and one species, from the Early Volkhov time onward; Dianulites with seven species, one of which is known from the Latorp time onward and six species, from the Early Volkhov onward; Dittopora with three species, two of which are known from the Latorp time onward and one species, D. sokolovi, from the Middle Volkhov time onward. The genera Diplotrypa and Phragmopora have a single species each, known from the Early Volkhov time; Anaphragma has two species, one of which is known from the Early Volkhov time onward and the other, A. verectum, from the Middle Volkhov onward; Hemiphragma has a single species, H. rotundatum, which appeared in the Middle Volkhov time. In the Middle Volkhov time the genera Hexapor ites with the species H. fungiformis, Monotrypa with M. jewensis, and Chyphotrypa with C. antiqua appeared. Bryozoans of the order Tubuliporida are represented by two genera Wollinella with one species W. baltica and Goryunovia with one species G. hemiseptata. In addition, in the Middle Volkhov of the Leningrad Region revealed bryozoans of the gen era Orbipora with species O. solida and O. acantho phora and Prophyllodictya with the species P. interme dia. These genera belong, respectively, to the families Aisenvergiidae (suborder Esthonioporina, order Tre postomida) and Ptilodictyidae (suborder Ptilodicty ina, order Cryptostomida) and were first recorded in the Tremadocian of China (see Chapter 6 for details). In the Middle Volkhov the first occurrences of six new species of the previously existed genera Orbipora, Prophyllodictya, Dittopora, Anaphragma, and Hemi phragma, belonging to the orders Trepostomida and Cryptostomida, and five species of five new genera, Hexaporites, Monotrypa, and Chyphotrypa (order Tre postomida) and Wollinella and Goryunovia (order Tubuliporida) have been recorded. The genus Hexaporites belongs to the previously known family

Explanation of Plate 19 Figs. 1 and 2. Dittopora annulata (Eichwald, 1860); (1) specimen PIN, no. 5075/436; (1a) longitudinal section of the colony, ×10; (1b) tangential section of the colony, ×10; (1c) tangential section of the region of the colony shown in Fig. 1b, ×40; (1d) tangential section of the region of the colony shown in Fig. 1b, ×40; (1e) tangential section of the region of the colony shown in Fig. 1b, ×40; Leningrad Region, Lava River, village of Vasil’kovo; Volkhov horizon, subhorizon BIIα; (2) specimen PIN, no. 5075/455; (2a) longitudinal section of the colony, ×10; (2b) cross section of the colony, ×10; (2c) tangential section of the colony, ×20; Len ingrad Region, Lava River, village of Vasil’kovo; Volkhov horizon, subhorizon BIIβ. PALEONTOLOGICAL JOURNAL

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Halloporidae, the genera Monotrypa and Chyphotrypa belong to the new family Anisotrypidae of the subor der Amplexoporina, the genera Wollinella and Goryunovia belong to the new family Phaceloporidae of the new suborder Paleotubuliporina. The Middle Volkhov deposits of the Leningrad Region have yielded 30 species of 16 genera, of which the bryozoans of the genera Esthoniopora, Dianulites, Dittopora, Anaphragma, and Prophyllodictya predomi nated. Here the first occurrences of 11 species, seven genera, four families, two suborders, and two orders have been recorded. At the boundary between the middle and upper Volkhov subhorizons, which approximately corre sponds to the boundary between the Dapingian and Darriwilian stages, two bryozoan species disappeared. Assemblage IV, upper Volkhov (Darriwilian Stage) (Fig. 20). This assemblage includes bryozoans of the orders Cystoporida, Trepostomida, Tubuliporida, and Cryptostomida. The order Cystoporida is represented by five species of two genera: Revalotrypa with three species, two of which are known from the Latorp time onward and one species, known from the Early Volkhov onward, and Lynnopora with two species, L. lunata and L. arborea, which appeared in the Late Volkhov time. The order Trepostomida is character ized by 27 species of 12 genera: Esthonioporella with one species, known from the Latorp time onward; Esthoniopora with three species, two of which are known from the Latorp time onward and one species, from the Early Volkhov onward; Dianulites with seven species, one of which is known from the Latorp time onward and six species, from the Early Volkhov onward; Dittopora with four species, two of which are known from the Latorp time onward, one species from the Middle Volkhov onward, and one more species, D. ramose, from the Late Volkhov onward; Phrag mopora with one species, known from the Early Volkhov time onward; Anaphragma with two species, one of which is known from the Early Volkhov time onward and one species, from the Middle Volkhov time onward; Diplotrypa with three species, one of which is known from the Early Volkhov time onward and two species, D. olgae and D. moniliformis, from the Late Volkhov time onward; Orbipora with two species, Hexaporites with one species, Hemiphragma with one species, Monotrypa with one species all known from the Middle Volkhov time onward; Eichwaldopora with one species E. ovulum, appeared in the Late Volkhov time. The order Tubuliporida is represented by a single

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genus, Wollinella, with one species, known from the Middle Volkhov time, and the order Cryptostomida is represented by a single genus, Prophyllodictya, with three species, one of which is known from the Middle Volkhov time onward and two species, P. putilovensis and P. gracilis, appeared in the Late Volkhov time. The Upper Volkhov horizon of the Leningrad Region has yielded 36 species of 16 genera, of which bryozoans of the genera Dianulites, Dittopora, Revalot rypa, and Hexaporites predominated. In deposits of the Upper Volkhov five new species of the previously existed genera belonging to orders Trepostomida and Cryptostomida have been revealed. In addition, three species of two new genera, Lynnopora (order Cysto porida) and Eichwaldopora (order Trepostomida), have been recorded. No new taxa with a rank higher than genus have been detected in the Upper Volkhov. At the boundary between the Volkhov and Kunda time 12 bryozoan species disappeared. CHAPTER 5. STAGES IN THE DEVELOPMENT OF THE LATORP–VOLKHOV BRYOZOANS Despite the lifetime of Latorp–Volkhov bryozoans was a relatively short span of geological time (about 8 Ma (Fedorov, 2004)) it is possible to discriminate three stages in their development. The first stage corresponds to the Latorp time. In the Latorp time the Baltic Basin was an extensive sea that stretched latitudinally from the west to the east of the Russian Platform as a result of the sea level rise after the Late Tremadocian regression. In that time it became connected with the Uralian basin (Nikishin et al., 1996). The Latorp Stage is characterized by a considerable migration in the Baltic Basin of a diverse fauna: echinoderms, ostracodes, etc. (Melnikova, 1999; Rozhnov, 2004, 2005). It is obvious that the first emergence of bryozoans in this basin (in the part that is now the Leningrad Region) can be dated to the Middle Latorp time. They were represented by 13 spe cies, seven genera, five families, and three suborders belonging to two orders: Cystoporida and Treposto mida. At the first stage of their development the Baltic bryozoans of these two orders had colonies predomi nantly of a hemispherical shape. These colonies were characterized by simple parallel or radial body plans, tubular cylindrical and tubular prismatic autozooecia, which had circular apertures in cystoporids and circu lar, rounded polygonal, and petaloid apertures in tre

Explanation of Plate 20 Figs. 1–3. Dittopora annulata (Eichwald, 1860); (1) specimen PIN, no. 5075/453; longitudinal section of the colony, ×10; Len ingrad Region, Lava River, village of Vasil’kovo; Volkhov horizon, subhorizon BIIβ; (2) specimen PIN, no. 5075/2; (2a) longitu dinal section of the colony, ×10; (2b) cross section of the colony, ×20; (2c) tangential section of the colony, ×40; Leningrad Region, Lynna River, village of Khamontovo; Volkhov horizon, subhorizon BIIγ; (3) specimen PIN, no. 5075/17; (3a) longitudi nal section of the colony, ×20; (3b) longitudinal section of the colony, ×20; (3c) cross section of the colony, ×20; Leningrad Region, Lynna River, village of Khamontovo; Volkhov horizon, subhorizon BIIγ. PALEONTOLOGICAL JOURNAL

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postomids. The colonies of Latorp bryozoans contain vesicular tissue, styles, and such types of heterozooe cia as neozooecia (order Cystoporida), mesozooecia, and heterozooecia similar to acanthozooecia (order Trepostomida). The autozooecia of Latorp treposto mids contain numerous hemiphragms. At the boundary between the Latorp and Volkhov time there was a brief regression, which was accompa nied by a break in sedimentation. At this boundary the disappearance of five bryozoan species has been recorded. The abrupt disappearance of some echino derm species at the boundary between the Latorp and Volkhov time also suggests the sea regression (Rozh nov, 2005). The second stage corresponds to the Early Volkhov time. In the relatively shallowwater part of the basin (now the Leningrad Region), bryozoans of the orders Cystoporida and Trepostomida persisted. They pre served the main features of the colonial morphology characteristic of the first stage of their development. However, in that time the suborder Amplexoporina with the family Stenoporidae evolved in the order Tre postomida. The bryozoans of this family possess such heterozooecia as exilazooecia. In addition, some tre postomid bryozoans evolved colonies with numerous diaphragms. This stage gave rise to a total of 19 bryo zoan species, eight genera, and six families belonging to four suborders of two orders. Very early in the Middle Volkhov the depth of the Baltic Basin abruptly increased as a result of the sea level rise (Kofman, 1971; Dronov, 1998, 1999, 2000). The diversity of bryozoans markedly increased not only because of the migration of bryozoans from other basins but also because of the appearance of new taxa of various ranks in this basin. The third stage corresponds to the Middle–Late Volkhov time. In the Middle Volkhov representatives of two new orders, Tubuliporida and Cryptostomida, appeared in addition to the bryozoans of the orders Cystoporida and Trepostomida. The bryozoans of the order Tubuliporida are char acterized by the development of rodshaped and recumbent colonies, with a serial body plan. They have tubular cylindrical autozooecia with rounded apertures, which open both on the frontal and lateral surfaces of the colony. Representatives of the order Cryptostomida are characterized by fenestrate fan shaped, ribbonlike, ribbonlike dendroid, and recum bent colonies. They have a bilateral body plan, tubular geniculate autozooecia and oval apertures, which open only on the frontal surface of the colony (Gor junova and Lavrentjeva, 1993; Gorjunova, 1992, 1996). In the Late Volkhov time the apertures of cysto porids acquired lunaria (Gorjunova and Koromyslova, 2008). In that time there is a wide diversity of rod shaped colonies of the order Trepostomida, in the autozooecia of which there were numerous dia phragms.

The transition from the Early to the Middle Volkhov time was the most significant period in the development of bryozoans of the Baltic Basin. In the Middle Volkhov time representatives of two new orders, two suborders, four families, seven genera, and 11 species appeared in the basin, the shape of colonies became more diverse, and the serial and bilateral body plans of colonies formed. In addition, the majority of Middle–Late Volkhov bryozoans of the order Trepos tomida have numerous diaphragms in autozooecia, which is evidence that the unstable position of polyp ides predominated. In the Middle Volkhov time there existed 30 species of 16 genera, in the Late Volkhov time there were 36 species, 16 genera, and ten families, which belonged to six suborders of four orders. The Middle Volkhov time corresponds to the max imum depth of the Baltic basin, whereas in the Late Volkhov time its depth gradually decreased (Kofman, 1971; Dronov, 2000). This event affected bryozoans by causing two species to disappear and eight new species to appear. At the boundary between the Volkhov and Kunda times, sea level abruptly dropped (Rozhnov, 2005). In that time, 12 bryozoan species apparently became extinct. CHAPTER 6. DISTRIBUTION OF THE OLDEST BRYOZOANS IN TIME AND SPACE This chapter deals with the distribution of bryozo ans in deposits of the Lower and Middle Ordovician in various regions of the world in order to determine the possible center of their origin and radiation. The schemes of the stratigraphic range of bryozoans are provided for each region individually (Figs. 21–24), as well as the global scheme (Fig. 25). In addition, the schemes of the geographical range of bryozoans are compiled for the Tremadocian, Floian, Dapingian, and Early Darriwilian time (Figs. 26, 27). These schemes are based on the map of the arrangement of the continents during the Tremadocian—Early Darri wilian ages (Cocks and Torsvik, 2004). 6.1. Stratigraphic Distribution of the Oldest Bryozoans in Various Regions of the World Until recently the encrusting problematic species Marcusodictyon priscum (Bassler, 1911) from the Tremadocian of Estonia was considered to be the old est bryozoan species. More recent investigations of M. priscum have shown that this species cannot be a bryozoan (Larwood and Taylor, 1979; Taylor, 1984; Gorjunova, 1986a). In addition, one more problem atic species, M. exspectans Mergl, 1984, which M. Mergl (1984, 2006) placed in the same genus, was described from the Lower Tremadocian of Bohemia. PALEONTOLOGICAL JOURNAL

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South China

At present the oldest bryozoans are known from the Lower Ordovician of South China (Fig. 21).

Tremadocian Stage (Lower Ordovician). In Hubei province the Fenxiang Formation (Paltodus deltifer conodont Zone) yielded bryozoans of two orders, Tre

2011 ? Aoro graptus victoriae

Paltodus deltifer Paltodus deltifer deltifer

Paltodus deltifer pristinus

Paroi Paroi stodus stodus origi navis nalis

Lenodus Lenodus antivariabilis variabilis

According to Xia et al., 2007, 2008

Conodonts

Graptolites

Formation

Conodonts

Graptolites

Time slice (TS)

Formation

Series

Conodonts

Revalotrypa huoi (Yang, 1957) Trepocryptopora dichotomata Yang, 1957 T. flabelata Yang, 1957

Hexaporites fungiformis Eichwald, 1860 Orbiramus grandis Xia in Xia et al, 2008 Prophyllodictia putilovensis Lavrentjeva, 1993 Batostoma jinbongshanense Yang et Xia, 1986 B. altunshanense Yang et Xia, 1986

Honhuayuan Fm.

Nekhorosheviella nodulifera Xia in Xia et al, 2007 Orbiramus normalis Xia in Xia et al, 2007 Orbiramus ovalis Xia in Xia et al, 2007 Orbiramus minus Xia in Xia et al, 2007 Nekhorosheviella semisphaerica Xia in Xia et al, 2007 Prophyllodictia prisca Xia in Xia et al, 2007

Serra tognathus diversus

Hunnegraptus copiosus

Tetra graptus appro ximatus

Paroi stodus triangu laris

Undulo graptus intersitus

Undulo graptus austro dentatus

According to Liu, 2009

Acanthograptus sinensis

1d Oepikodus evae

3a

Prioniodus Balto hong hiodus huayua com nensis munis

Darriwilian

Yangtzepla cognathus crassus

4a

Fenxiang Fm.

2a Expanso Exigra ptus graptus cla vus hirundo

Baltonidus norrian dicus

Kuni utan Fm.

4b

Serratoganthus diversus

Azygo graptus suecicus

Dawan Fm.

Micro zarkodina parva

Graptolites

Zones of the Leningrad Region

Paltodus deltifer

2b Acro Didymo Corymbo graptus grap graptus filli tellus formis eobifidus deflexus

2c

Tetra graptus appro ximatus

Baltoniodus triangularis

Dawanian

Balto niodus navis

Hunnegraptus copiosus

3.7

3b

Acanthograptus sinensis

3.2 Lenodus variabilis

Hunghuayuan Fm.

1.9

Oepikodus evae

Not detected

GSS

Duration (in Ma) (according to Fedorov, 2004)

Formation Member

Horizons, subhorizons codes of subhorizons

System Series Stage Stage Group

Koren and Tolmache Web Tolmache va, 2002 va, 2005 by from Korenfrom Koren et al., et al., 2006 et al., 2006 2004 Eoplacog nathus 1.1 pseudo planus

Fenghsiang Fm.

BIIα

Yushanian

1.6 Expansograptus hirundo

1.1

Phyllograptus angusti folius tenuis

BIIIα

Ichangian

BIIβ

Volkhov Zheltyaki

Kunda Lower Middle Upper

1.1

Prioniodus elegans

Volkhov Middle BIIIβ

Undulograptus austrodentatus

Frizy 1.5

Dikari

Upper BIIγ

Lower BIIIγ

Paroistodus proteus

Pseudo phyllo graptus densus

Billingen

Oelandian

Dapingian Arenig

Middle Ordovician Darriwilian Llanvirn


Paltodus deltifer

BIA Tetra graptus phyll graptoides

Leetse

Latorp BIB

Not detected

Hunnebergian

Floian

Ordovician ISS

Varanguan

Tremadocian Tremadoc

Lower Ordovician

BRYOZOANS OF THE LATORP AND VOLKHOV HORIZONS 955

South China

Fig. 21. Distribution of bryozoans in the Lower and Middle Ordovician (Tremadocian–Darriwilian stages) of South China (based on data of Yang, 1957; Gorjunova, 1996; Xia et al., 2007).

postomida (family Aisenvergiidae) and Cryptostomida (family Ptilodictyidae). The first of these orders is rep resented by five recently established species of the two genera Nekhorosheviella Modzalevskaya, 1953 and Orbiramus Xia in Xia et al., 2007: Nekhorosheviella nodulifera, N. semisphaerica, Orbiramus normalis, O. ovalis and O. minus. And the second order is repre

956

KOROMYSLOVA Ordovician

Arenig

Middle

Upper

BIB

BIIα

BIIγ

3.7

Dikari 1.9

BIIβ Volkhov Zheltyaki 1.6

1.1

1.1 Not detected

Eoplaco gnathus pseudoplanus

Yangtzepla cognathus crassus Dentatus

Undulograptus austrodentatus Histiodella sinuosa

Oncograptus upsilon

M.divergens

Histiodella altifrons

1.1

Lehman

Histiodella holodentata

Lenodus variabilis

Baltonidus norriandicus


Expansograptus hirundo Isograptus v. victoriae

Tripodus laevis

Member

Frizy 1.5


Phyllograptus angustifolius tenuis Baltoniodus inangularis

Isograptus v. lunatus

Didymograptus bifidus Reutterodus andinus

Pendeograptus fruticosus

Akzharensis

Regional (Balto scandia) Horizons, and local subhorizons (Lenin Lower Middle Upper grad Region) strati BIIIα BIIIβ BIIIγ Codes of horizons graphic subdi Formation visions

Whiterockian Kanosh

Wahwan Juab

Oepikodus communis

Acoduc deltatus Oneotodus costatus

Tetragraptus approximatus

Ibexian Fillmore

Baltoniodus navis

Pseudo phyllograptus densus Prioniodus elegans

Tetragraptus phyllo graptoides

Not detected

Paroistodus proteus

Oepikodus evae

Leetse 3.2

Group

Lower

BIA

Series

Kunda

Billingen

Isograptus v.maximus

Hunne bergian

Llanvirn

Oelandian Volkhov

Latorp

Series Stage


Graptolites Koren and Tolmacheva, 2002 Zones from Koren of the et al., 2006 Lenin Conodonts grad Tolmacheva, Region 2005 from Koren et al., 2006 Series Formation, western Utah

Callotheca

Trema doc

Adelograptus victoriae

Middle Ordovician Darriwilian

Dapingian

Polonicus

Lower Ordovician Floian

Trema docian

Inter national Strati graphic Scale General Strati graphic Scale

System

San Juan

Graptolites Webby et al., 2004

North Zo America nes

Conodonts Webby et al., 2004

Niquivilia

Formation Zo Argen (Carrera and nes tina Cech, 2003)

?Ceramopora unapensis Ross, 1966 Orbipora utahensis (Hinds, 1970) Dianullites fastigiatus Eichwald, 1829 Nicholsonella sp. A Nicholsonella sp. B Ibexella multidiaphragmata Ernst, Taylor et Wilson, 2007 Kanoshopora droserae Ernst, Taylor et Wilson, 2007 Eridotrypa hindsi Ernst, Taylor et Wilson, 2007 ?Diplotrypa sp. Batostoma sp. Amplexopora? sp. Nicholsonella sp. Eridotrypa subtilis Bork and Perry, 1968 Phyllodictya crystalaria Hinds, 1970


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Fig. 22. Distribution of bryozoans in the Lower and Middle Ordovician of North America and Argentina (based on data of Ross, 1966; Hinds, 1970; McLeod, 1978; Dzik, 1981; Tuckey, 1990; Wilson et al., 1992; Taylor and Wilson, 1999; Carrera, 1995; Car rera and Cech, 2003; Taylor and Ernst, 2004).

sented by one species of the genus Prophyllodictya Gorjunova in Gorjunova and Lavrentjeva, 1987: P. prisca (Xia et al., 2007; Zhang et al., 2009). It is worth noting that in other regions of the world the genus Prophyllodictya is only known from the Middle Dapingian Stage onward (Gorjunova and Lavrentjeva, 1987, 1993), and Nekhorosheviella is only known from the Katian Stage of the Upper Ordovician (Modza levskaya, 1953), thus giving this assemblage a younger appearance. Xia et al. (2007) correlate the deposits of the Fenxiang Formation with the Hunneberg subhori zon; however, according to data of Tolmacheva (Tol macheva et al., 2001), Webby (Webby et al., 2004), Ershova (Ershova and Fedorov, 2006; Ershova, 2008), Koren (Koren et al., 2006), Nõlvak (Nõlvak et al., 2007), Bergström (Bergström et al., 2009) the Paltodus deltifer Zone should correspond to the Varanguan horizon. Therefore, the age of bryozoans is deter mined as Varanguan (Early Tremadocian). Figure 21 shows the comparison of the schemes of correlation of the Fenxiang Formation according to Xia et al., 2007 and Liu, 2009 with the International and General Stratigraphic Scales, as well as with the regional (Bal toscandia) and local (Leningrad Region) stratigraphic subdivisions. Floian Stage (Lower Ordovician). In Anhui prov ince the upper part of the Hunghuayuan Formation, Time Slice (TS) 2c, yielded bryozoans of two orders: Trepostomida (families Aisenvergiidae and Hal loporidae) and Cryptostomida (family Ptilodictyidae) (Xia et al., 2008). The first of these orders is repre sented by two species of two genera: Orbiramus with O. grandis and Dianulites Eichwald, 1829 with D. hexaporites (hereinafter referred to as Hexaporites 10

fungiformis , the second order is represented by one species of the genus Prophyllodictya, P. putilovensis. Xia et al. (2008) assign TS 2c to the Hunghuayuan Formation, whereas Liu (2009) correlates TS 2c with the Dawan Formation. However, in any case TS 2c is a part of the Floian Stage (Webby et al., 2004; Nõlvak et al., 2007) and correlates with the Billingen subhori zon of the Leningrad Region (Webby et al., 2004; Liu, 2009) (Fig. 21). The Darriwilian Stage (Middle Ordovician). More recent bryozoans are known in South China from the provinces of Xinjang (Yin and Xia, 1986) and Shensi (or Shaanxi) (Yang, 1957; Kobayashi, 1960) (Fig. 21). In Xinjang province bryozoans are confined to the lower part of the Malieziken Group. Yin and Xia (1986) assign these deposits to the Upper Arenigian 10 Based

on Pushkin’s paper (Pushkin and Popov, 2005), the spe cies Dianulites hexaporites (Pander, 1830) will hereinafter be referred to as Hexaporites fungiformis Eichwald, 1860). PALEONTOLOGICAL JOURNAL

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(lower part of the Darriwilian Stage). The bryozoans belong to the order Trepostomida (family Monticuli poridae) and are represented by the genus Batostoma Ulrich, 1882 with two species, B. jinhongshanense and B. altunshanense (Yin and Xia, 1986) (Fig. 21). In Shensi (or Shaanxi) province bryozoans come from the Yangtzeella poloi brachiopod Zone and beds with Didymograptus sp. (Yang, 1957; Kobayashi, 1960). Yang (1957) correlated these deposits with the upper part of the Lower Ordovician. In 1960 the Ichang Series belonged to the Lower Ordovician of China and corresponded to the Tremadocian, Areni gian, and Llanvirnian of Great Britain (Zhang, 1960). Now this interval is divided into four series, where the Ichangian corresponds to the Tremadocian; the Yush anian, Dawanian and the lower part of the Darriwilian corresponds to the Arenigian; and the upper part of the Darriwilian corresponds to the Llanvirnian (Webby et al., 2004). According to Turvey and Siveter (2007) the Yangtzeella poloi Zone in Shensi province belongs to the Kuniutan Formation (Darriwilian Stage) (Liu, 2009) and correlates with the Kunda hori zon of the Leningrad Region of Russia (Fig. 21). Bry ozoans of the province Shensi are represented by the orders Cystoporida (family Revalotrypidae) and Cryp tostomida (family Intraporidae). The first family com 11

prises the genus Revalotrypa Bassler, 1911 with the species R. huoi, the second family comprises the genus Trepocryptopora Yang, 1957 with two species, T. dichotomata and T. flabelata. Laurentia Tremadocian?–Floian stages (Lower Ordovician). The most ancient bryozoans on the continent Lauren tia were recorded in Oklahoma, the United States, Kindblade Formation, Arbuckle Group, Canadian Stage. They belong to the order Cystoporida (family Ceramoporidae) and are represented by one species ?Ceramopora unapensis Ross, 1966 (Ross, 1966; Dzik, 1981; Tuckey, 1990) (Fig. 22). According to Hintze (1973), the Canadian corresponds to the Tremadocian and Arenigian of Great Britain; according to Robson and Pratt (2001), its upper part (Kindblade Forma tion) belongs to the Tetragraptus Zone, which corre sponds to the upper part of the Hunneberg and the base of the Billingen subhorizons of the Leningrad Region (Floian Stage) (Koren et al., 2006). According to Ethington and Clark (1981), the Kindblade Forma tion corresponds to the Oepikodus communis– “Microzarkodina” marathonensis conodont zones, 11Yang

(1957) described this species as Nicholsonella huoi Yang, 1957. And Gorjunova (1988) placed it in the genus Revalotrypa.

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1b 1 mm

1a 1 mm

2a

1 mm

3 1 mm 2b

1 mm


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which also correlate with the upper part of the Hun neberg and the base of the Billingen subhorizons of the Leningrad Region (Floian Stage) (Webby et al., 2004). According to Tuckey (1990), the Kindblade Forma tion belongs to the Upper Tremadocian. Floian Stage (Lower Ordovician). This stage com prises the upper part of the Fillmore Formation of Western Utah (United States). This stage yielded bry ozoans of the order Trepostomida of the families Aisenvergiidae, Orbipora utahensis (Hinds, 1970; Wil son et al., 1992), and Halloporidae, Dianulites fastigi atus (Taylor and Wilson, 1999) (Fig. 22). The upper part of the Fillmore Formation correlates with the Billingen subhorizon of the Leningrad Region (Ething ton and Clark, 1981; Wilson et al., 1992; Taylor and Wilson, 1999; Taylor and Ernst, 2004). In addition, bryozoans D. fastigiatus have been encountered in Arkansas and Missouri (United States) within the Ozark Plateau in the Canadian or, more exactly, in the Cassinian, Black Rock, Didymograptus bifidus Zone (Decker, 1935; McLeod, 1978). The Cassinian is the upper part of the Canadian (Kay, 1960), and it corre sponds to the Billingen Subhorizon of the Leningrad Region (McLeod, 1978; Dzik, 1981; Taylor and Wil son, 1999). Dapingian Stage–Lower Darriwilian Substage (Middle Ordovician). In deposits of the Kanosh For mation (Whiterockian, Kanosh Formation, His tiodella altifrons Zone) in Western Utah (United States) were established bryozoans of the order Tre postomida: Orbipora utahensis, Ibexella multidiaphrag mata, and Kanoshopora droserae of the family Aisen vergiidae; ?Diplotrypa sp. of the family Halloporidae; Eridotrypa subtilis, E. hindsi, Batostoma sp. and Nicholsonella sp. of the family Monticuliporidae; Amplexopora? sp. of the family Stenoporidae (Hinds, 1970; Ernst et al., 2007) (Fig. 22). The deposits con taining these bryozoans correlates with the middle and upper parts of the Volkhov horizon of the Leningrad Region (Webby et al., 2004; Ernst et al., 2007). The Lehman Formation in Utah, corresponding to the base of the Darriwilian Stage, also yielded bryozo ans (Hinds, 1970). They belong to the order Cryp tostomida and are represented by one species of the genus Phillodictya, Ph. crystalaria (Fig. 22). Novaya Zemlya In deposits of the Nelidovo horizon (Lower–Mid dle Ordovician, Tremadocian–Darriwilian stages) of the VaygachSouthern Novay Zemlya Structural Facies Zone, bryozoans are restricted to Novaya Zem

959

lya and are represented by the orders Cystoporida and Trepostomida (Astrova, 1965; Bondarev et al., 1965, 1968; Nekhorosheva, 1968, 1970). The first order comprises the genera Revalotrypa (family Revalotryp idae), Ceramopora and Lamtshinopora (family Cera moporidae), Profistulipora (family Anolotichiidae), the second order comprises Dianulites and Diplotrypa (family Halloporidae), Nicholsonella and Stigmatella (family Monticuliporidae), Cyphotrypa (family Ste noporidae). Avalonia The Floian Stage (Lower Ordovician). In Southern Wales (Carmarthen region), this stage comprises the Arenigian Series, Moridunian Stage (Moridunian), upper member of the Ogof Hen Formation, T. phyl lograptoides Zone. This stage yielded isolated speci mens of bryozoans of the order Trepostomida; i.e., Orbipora sp. of the family Aisenvergiidae (Taylor and Cope, 1987) (Fig. 23). The Ogof Hen Formation cor relates with the lower Latorp horizon (Hunneberg subhorizon) of the Leningrad Region (Webby et al., 2004; Taylor and Ernst, 2004). Dapingian Stage–Lower Darriwilian Stage (Mid dle Ordovician). The Upper Arenigian (Tourmakeady Limestone, Isograptus gibberus–Didymograptus (Expansograptus) hirundo Zone) of Ireland also yielded some isolated specimens of bryozoans of the order Phylloporinida: Alwynopora orodamus of the family Enalloporidae (Taylor and Curry, 1985). The Isograptus gibberus Zone correlates with the lower and middle parts of the Volkhov horizon, and the Didymograptus (Expansograptus) hirundo Zone corre lates with the upper part of the Volkhov horizon and the lower part of the Kunda horizon of the Leningrad Region (Webby et al., 2004; Koren et al., 2004) (Fig. 23). Baltia The Floian Stage (Lower Ordovician). The Latorp horizon corresponds to this stage in Baltia. This hori zon in the Leningrad Region of Russia yielded the old est bryozoans (see Chapter 4 for details). They are rep resented by two orders: Cystoporida (family Revalot rypidae) and Trepostomida (families Esthonioporidae, Halloporidae, Phragmoporidae, and Monticuli poridae) (Modzalevskaya, 1953, 1986; Gorjunova, 1988, 1992, 1996; Pushkin and Popov, 1999). Accord ing to Pushkin and Popov’s data (1999) the species Hemiphragma priscum (order Trepostomida) is the

Explanation of Plate 21 Figs. 1–3. Dittopora annulata (Eichwald, 1860); (1) specimen PIN, no. 5075/136; (1a) longitudinal section of the colony, ×20; (1b) cross section of the colony, ×40; Leningrad Region, Lynna River, village of Khamontovo; Volkhov horizon, subhorizon BIIγ; (2) specimen PIN, no. 5075/138; (2a) longitudinal section of the colony, ×20; (2b) tangential section of the colony, ×40; age and locality as in Fig. 1; (3) specimen PIN, no. 5075/160; longitudinal section of the colony, ×20; the same age and location. PALEONTOLOGICAL JOURNAL

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KOROMYSLOVA

1.5

Baltonidus norriandicus

1.6

Microzarkodina parva

angustifolius tenuis Pseudo phyllograptus densus

Latorp

Leetse

Billingen BIB

Trema doc

Hunne B bergian IA

Isograptus gibberulus Baltoniodus navis

1.9 Phyllograptus

Auloograptus cucullus (Didymograptus (Expansograptus) hirundo)

Baltoniodus inangularis

Oepikodus evae

3.7

Moridunian

Lower BIIα

Expansograptus hirundo

Prioniodus elegans

3.2

Tetragraptus phyllograptoides Not detected

Alwynopora orodamus Taylor et Curry, 1985

Frizy

Middle BIIβ

Lenodus variabilis

Volkhov Zheltyaki

Oelandian Volkhov

BIIγ


Paroistodus proteus

Expansograptus simulans

Corymbograptus varicosus

? Tetragraptus phyllograptoides

Orbipora sp.

1.1

Fennian

Lower BIIIα


Arenig

1.1

Didymograptus artus

Whitlandian

Middle BIIIβ

Dikari

Kunda

Not detected

Series Stage

Eoplacognathus pseudoplanus

1.1

Upper BIIIγ

Zones based on graptolites Gradstein et al., eds., 2004 from Koren et al., 2006

Llanvirn Abereiddian

Graptolites Koren and Conodonts Tolmacheva, Tolmacheva, 2005 2002 from Koren from Koren et al., 2006 et al., 2006

Great Britain

Migne intian

Codes of horizons Formation Member

Group

Series Llanvirn

Horizons, subhorizons

Zones of the Leningrad Region

Trema doc

Trema docian


Upper

Arenig

Dapingian

General Strati graphic Scale


Ordovician

Middle Ordovician Darriwilian

System Series Stage

International Stratigraphic Scale


960

Araneograptus murray

Fig. 23. Distribution of bryozoans in the Lower and Middle Ordovician (Arenigian) of Great Britain (based on data of Taylor and Curry, 1985; Taylor and Cope, 1987).

Explanation of Plate 22 Fig. 1. Anaphragma verectum Koromyslova, sp. nov.; holotype PIN, no. 5075/1; (1a) longitudinal section of the colony, ×5; (1b) longitudinal section of the same region of the colony, ×30; (1c) cross section of the colony, ×10; (1d) tangential section of the colony, ×40; (1e) tangential section of the colony, ×20; Leningrad Region, village of Khamontovo, Lynna River; Volkhov horizon, subhorizon BIIγ. PALEONTOLOGICAL JOURNAL

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961 Plate 22

1 mm

1b 1a

1 mm

1e 1 mm 1 mm

1c

1d


1 mm

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KOROMYSLOVA

oldest, since it occurs in the deposits belonging to the uppermost Prioniodus elegans conodont Zone (see Fig. 20). In Estonia and Belarus, which belong to the same (EstonianLithuanian) facial zone as the Lenin grad Region, no bryozoans have been discovered in Latorp deposits (Männil, 1959; Pushkin, 1987b; Gor junova, 1996). Dapingian Stage–Lower Darriwilian Substage (Middle Ordovician). Within Baltia this interval corre sponds to the Volkhov horizon. Bryozoans from Volkhov deposits are known in the Leningrad Region of Russia (see Chapter 4 for details), Estonia, and Belarus. They generally belong to five orders: Cysto porida (family Revalotrypidae), Trepostomida (fami lies Aisenvergiidae, Esthonioporidae, Halloporidae, Ralfimartitidae, Monticuliporidae, Stenoporidae, and Anisotrypidae), Rhabdomesida (family Goldfussitryp idae), Tubuliporida (family Phaceloporidae), and Cryptostomida (family Ptilodictyidae). However it is worth noting that Tubuliporida are absent from the Volkhov bryozoans of Estonia, and Rhabdomesida are absent from the coeval bryozoans of the Leningrad Region. There is the following information on the Volkhov bryozoans of Estonia: ⎯The lower part of the Volkhov horizon contains bryozoans of three orders: Cystoporida (family Reval otrypidae), Trepostomida (families Esthonioporidae, Halloporidae, Ralfimartitidae and Monticuliporidae), and Rhabdomesida (family Goldfussitrypidae). The order Cystoporida is represented by one species of the genus Revalotrypa, the order Trepostomida is repre sented by seven species of four genera: Esthoniopora with three species; Ralfimartites Gorjunova, 2005 with one species; Diplotrypa with two species; and Dittopora with one species, the order Rhabdomesida is repre sented by one species of the genus Goldfussitrypa Bassler, 1952 (Fig. 24). ⎯The middle part of the Volkhov horizon contains bryozoans of four orders: Cystoporida, Trepostomida, Rhabdomesida, and Cryptostomida. The order Cysto porida is represented by one species of the genus Revalotrypa, the order Trepostomida is represented by eight species of four genera: Esthoniopora with three species, Ralfimartites with one species, Diplotrypa with two species, and Dittopora with two species, the order Rhabdomesida is represented by one species of the genus Goldfussitrypa Bassler, 1952, and the order Cryptostomida is represented by one species of the genus Prophyllodictya (Fig. 24). ⎯The upper part of the Volkhov horizon contains bryozoans of four orders: Cystoporida, Trepostomida, Rhabdomesida, and Cryptostomida. The order Cysto porida is represented by one species of the genus

Revalotrypa, the order Trepostomida is represented by nine species four genera: Esthoniopora with three spe cies, Ralfimartites with one species, Diplotrypa with three species, and Dittopora with two species, the order Rhabdomesida is represented by one species of the genus Goldfussitrypa, and the order Cryptostomida is represented by one species of the genus Prophyllod ictya (Fig. 24). There are bryozoans in core material from bore holes in the Volkhov horizon in Belarus; however, the strong secondary dolomitization of rocks prevents their taxonomic determination. Pushkin (1987b) believed that they are similar in composition to the bryozoans of the Volkhov horizon of the Leningrad Region and Estonia. Argentine Precordillera Dapingian Stage (Middle Ordovician). Bryozoans are known from the San Juan Formation and belong to the Niquivilia brachiopod Zone and Tripodus laevis conodont Zone (Carrera, 1995; Carrera and Cech, 2003). They belong to the order Trepostomida (family Monticuliporidae) and are represented by the genus Nicholsonella Ulrich, 1890. Carrera (1995) described two species of this genus, designated as sp. A. and sp. B. The Niquivilia and T. laevis zones correlate with the base of the North American Whiterockian Series (Carrera and Cech, 2003), which in turn correlates with the base of the Volkhov horizon of the Leningrad Region (Fig. 22). Other Regions In other regions of the world bryozoans appeared considerably later, from the end of the Darriwilian Age. On the Taimyr Peninsula the earliest bryozoans are known from the Middle Ordovician onward (Engelhardt Horizon, Hustedograptus teretiusculus Zone) (Nekhorosheva, 1966). The Engelhardt hori zon correlates with the upper part of the Darriwilian Stage of the Ukhaku Horizon (Koren et al., 2006). Bryozoans are represented by the orders Trepostomida (Nicholsonella, Trematopora, and Orbipora) and Cryp tostomida (Proavella, Rhinidictya, and Pachydictya). On Severnaya Zemlya the earliest bryozoans were established on October Revolution Island. They were encountered in the lower and middle parts of the Lake Formation, belonging to the Middle Ordovician (Nekhorosheva, 2002), and are only represented by one species of the order Trepostomida, Halloporina severozemelica Nekhorosheva, 2002. On the Siberian platform most ancient bryozoans have been revealed in the Middle Ordovician (Volgian horizon), which cor

Fig. 24. Distribution of bryozoans in the Middle Ordovician (Volkhov and Kunda horizons) of Estonia (based on data of Bassler, 1911; Gorjunova and Lavrentjeva, 1987, 1993; Gorjunova, 1986b; 1996, 2005; Pushkin and Popov, 2001; Koromyslova, 2005b; Koromyslova, 2007). PALEONTOLOGICAL JOURNAL

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BRYOZOANS OF THE LATORP AND VOLKHOV HORIZONS Ordovician

Arenig

BIIβ BIIγ Volkhov Zheltyaki Frizy 1.6 1.5

BIIIα BIIIβ

BIIIγ

Regional (Balto scandia) Horizons, and local subhorizons (Lenin grad Region) strati Codes of horizons graphic subdi Formation visions

Member

1.1

1.1


Not detected


1.1

Lenodus variabilis

Beds with A.(?) lepidurus Baltonidus norriandicus


Baltoniodus inangularis

M. estonica Zone

M. polyphemus Baltoniodus Zone navis

Phyllograptus angustifolius tenuis

Pseudo phyllograptus densus

Oepikodus evae

Prioniodus elegans

Upper LowerMiddleUpper

Expansograptus hirundo

Dikari 1.9

3.7

Tetragraptus phyllo graptoides

Paroistodus proteus

Not detected

3.2

BIIα

Middle

Beds with A.(?) broeggeri

BIB Leetse

Kunda

A. (A.) expansus Zone

Lower

Series


Graptolites Koren and Tolmacheva, 2002 from Koren et al., 2006 Conodonts Tolmacheva, 2005 Zones from Koren et al., 2006 Trilobites Ivantsov, 1997

Dittopora clavaeformis Dybowski, 1877 Esthoniopora lessnikowae (Modzalevskaya, 1953) Ralfimartites honoratus Gorjunova, 2005 Revalotrypa gibbosa Bassler, 1911 Esthoniopora curvata Bassler, 1911 E. communis Bassler, 1911 Diplotrypa petropolitana Nicholson, 1879 D. bicornis (Eichwald, 1829) Goldfussitrypa abnormis Dittopora annulata (Eichwald, 1860) Prophyllodictia intermedia Gorjunova, 1987 Diplotrypa moniliformis Bassler, 1911 Orbipora solida Bassler, 1911 Dianulites fastigiatus Eichwald, 1829 D. janischewskyi Modzalevskaya, 1953 Phragmopora multiporata Bassler, 1911


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Inter national Strati graphic Scale General Strati graphic Scale

Group

Oelandian Volkhov

Latorp

BIA

Llanvirn

Eoplaco

Trema doc

A. (K.) pachyo gnathus phthalmus A. (K.) minor Zone pseudoplanus

Trema docian

System Series Stage

Middle Ordovician Dapingian Darriwilian

A. (K.) striatus A. (K.) "raniceps" Zone


963

2011

964

KOROMYSLOVA Ordovician Lower Ordovician Tremadocian Floian

System Series Stage

Middle Ordovician Dapingian Darriwilian

Tremadoc

Arenig

Llanvirn

Oelandian Varanguan

Latorp Hunnebergian BIA

Billingen BIB Leetse

2

3.2

3.7

Volkhov Lower Middle Upper BIIα BIIβ BIIγ Volkhov Dikari Zheltyaki Frizy 1.9

1.6

1.5

Kunda Lower Middle Upper

BIIIα

BIIIβ

BIIIγ

1.1

1.1

1.1

Series

Interna tional Strati graphic Scale General Strati graphic Scale

Group Horizons, subhorizons

Regional (Balto scandia) and local (Lenin Codes of horizons grad Region) Formation strati graphic Member Duration (in subdivisions Ma) (according to Fedorov, 2004)

Nekhorosheviella Modzalevskaya, 1953 Orbiramus Xia in Xia et al., 2007 Prophyllodictya Gorjunova in Gorjunova et Lavrentjeva, 1987 Ceramopora Hall in Silliman, Silliman et Dana, 1851 Orbipora Eichwald, 1856 Hemiphragma Ulrich, 1893 Dianulites Eichwald, 1829 Dittopora Dybowskii, 1877 Esthoniopora Bassler, 1911 Phragmopora Vinassa de Regny, 1921 Revalotrypa Bassler, 1911 Esthonioporella Modzalevskaya, 1953 Hexaporites Pander, 1830 Nicholsonella Ulrich, 1890 Ralfimartites Gorjunova, 2005 Anaphragma Ulrich et Bassler, 1904 Diplotrypa Nicholson, 1879 Goldfussitrypa Bassler, 1952 Batostoma Ulrich, 1882 Alwynopora Taylor et Curry, 1985 Chyphotrypa Ulrich et Bassler, 1904 Gorjunovia Taylor et Rozhnov, 1996 Monotrypa Nicholson, 1879 Wollinella Dzik, 1981 Ibexella Ernst, Taylor et Wilson, 2007 Kanoshopora Ernst, Taylor et Wilson, 2007 Eridotrypa Ulrich, 1893 Amplexopora? Ulrich, 1882 Lynnopora Gorjunova et Koromyslova, 2008 Eichwaldopora Pushkin et Popov, 2005 Phyllodictya Ulrich, 1882 Trepocryptopora Yang, 1957

Fig. 25. Distribution of bryozoan genera in the Lower and Middle Ordovician (Tremadocian–Darriwilian stages) (based on data of Bassler, 1911; Modzalevskaya, 1953, 1986; Yang, 1957; Ross, 1966; Hinds, 1970; McLeod, 1978; Dzik, 1981; Taylor and Curry, 1985; Taylor and Cope, 1987; Gorjunova and Lavrentjeva, 1987, 1993; Gorjunova, 1988, 1996, 2005; Taylor and Rozhnov, 1996; Tuckey, 1990; Wilson et al., 1992; Taylor and Wilson, 1999; Pushkin and Popov, 1999, 2001, 2005; Taylor and Ernst, 2004; Koromyslova, 2004b, 2007; Xia et al., 2007; Gorjunova and Koromyslova, 2008 with modifications, including new data).

relates with the upper part of the Darriwilian Stage of the Lasnamägi Horizon (Koren et al., 2006). These bryozoans belong to two orders: Trepostomida (genera Dianulites, Spatiopora, Diplotrypa, Hallopora, Batostoma, Homotrypa, and Mesotrypa) and Cryp tostomida (genus Pachydictya) (Kanygin et al., 1984). From the areas that in the Ordovician belonged to the

seas of the continent of Gondwana, bryozoans have been recorded from the Upper Ordovician onward: the Pin Formation in India (Suttner and Ernst, 2007) and Australia (Ross, 1961). Figure 25 shows the global scheme of the distribu tion of bryozoan genera in the Lower and Middle Ordovician (Tremadocian–Lower Darriwilian stages). PALEONTOLOGICAL JOURNAL

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965

Tremadocian (Varanguan) time

New Siberian Islands

Siberia

Ptilodictyidae

Taim yr

Kazakhstan

Argentine Precordillera

Tarim

South China

ca Perunica ori Arm 13a

Av alo nia

Lauren tia

Baltica

Aisenvergiidae

South Pole 15b 15a

60S Mexican Terrane

Gondwana

30S

Ceramoporidae ?

Tremadocian (Early Hunnebergian) time


Siberia Taim yr

Kazakhstan

Tarim

South China


13a Av alo nia

Lauren tia

Baltica

South Pole 15b 15a

60S Mexican Terrane

Gondwana

30S

Explanation 1

2

3

Fig. 26. Distribution of bryozoans in the Tremadocian time (based on Ross, 1966; Taylor and Cope, 1987; Tuckey, 1990; Wilson et al., 1992; Taylor and Wilson, 1999; Taylor and Ernst, 2004; Xia et al., 2007 with modifications, including new data). Explana tion: (1–3) orders: (1) Trepostomida, (2) Cystoporida, (3) Cryptostomida. PALEONTOLOGICAL JOURNAL

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KOROMYSLOVA

Ceramoporidae ?

Floian (Late Hunnebergian) time


Siberia Taim yr

Kazakhstan Baltica

13a Av alo nia

Lauren tia


South Pole 15b 15a

60S

Aisenvergiidae

Tarim

South China

Mexican Terrane

Gondwana

30S

Revalotrypidae Ceramoporidae ?

Floian (Billingen) time

Esthonioporidae Halloporidae

Aisenvergiidae New Siberian Islands

Halloporidae

Phragmoporidae Monticuliporidae

Siberia Taim yr

Kazakhstan Baltica


13a Av alo nia

Lauren tia

Ptilodictyidae Tarim

South China

Aisenvergiidae

South Pole

Halloporidae 15b 15a

60S Mexican Terrane

Gondwana

30S

Explanation 1

2

3


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6.2. Geographic Distribution of the Oldest Bryozoans Tremadocian Age Varanguan time. Based on data presented in the first part of this chapter it would appear reasonable that the oldest bryozoans inhabited an Early Ordovician basin in South China that was located between 60° and 30° S in the temperate zone. They were represented by two orders Trepostomida (family Aisenvergiidae) and Cryptostomida (family Ptilodictyidae) (Fig. 26). Early Hunnebergian time. The species ?Cera mopora unapensis from the Kindblade Formation (Kindblade Formation) in Oklahoma, United States, according to data of different authors may be both Tremadocian (Early Hunnebergian) and Floian (Late Hunnebergian–Billingen) (see 6.1 for details). There fore, it would appear reasonable that in this time span the North American basin was inhabited by isolated bryozoan species of the order Cystoporida (family Ceramoporidae) (Figs. 26, 27). This was probably a warmwater basin, since it was located between 30° S and the equator in the subtropical or tropical zone. Floian Age Late Hunnebergian time. There are data on bryozo ans from two basins: North American and Avalonian. In that time the North American basin was probably still inhabited by bryozoans of the order Cystoporida (fam ily Ceramoporidae), and the Avalonian basin was inhabited by isolated representatives of the order Tre postomida that belonged to the family Aisenvergiidae (Fig. 27). The Avalonian basin was located between 30° and 60° S in the temperate belt. Perhaps, Aisen vergiidae migrated from the South Chinese basin to the Avalonian basin. Billingen time. There are data on bryozoans from three basins: North American, South Chinese, and Baltic (Fig. 27). The North American basin, where bryozoans of the order Cystoporida (family Cera moporidae) dwelt, in this period was inhabited by rep resentatives of the order Trepostomida of the families Aisenvergiidae and Halloporidae. The South Chinese basin was in that time inhabited by bryozoans of the orders Trepostomida (families Aisenvergiidae and Halloporidae) and Cryptostomida (family Ptilodicty idae), and the Baltic basin was inhabited by bryozoans of the orders Cystoporida (family Revalotrypidae) and Tre postomida (families Esthonioporidae, Halloporidae, Phragmoporidae, Monticuliporidae). The Baltic basin was located in the temperate zone between 30° and 60° S. In the Billingen time all three basins shared the family; in addition, the North American and South

967

Chinese basins shared the family Aisenvergiidae. It would appear reasonable that bryozoans Aisenvergi idae migrated from the South Chinese or Avalonian basins to the North American basin. It seems likely that bryozoans Halloporidae appeared simultaneously in all three basins. Representatives of this family were perhaps the first to emerge in the Baltic basin. It is by no means improbable that they could migrate from the North American or South Chinese basins and invade it to give rise to other families. This is supported by the fact that in the Billingen time the Baltic basin con tained numerous endemic forms; i.e., species of the families Revalotrypidae, Esthonioporidae, Phrag moporidae, and Monticuliporidae. Dapingian Age Early Volkhov time. There are data on bryozoans from three basins: Avalonian, Argentine, and Baltic. The Avalonian basin was inhabited in that time by bry ozoans of the order Phylloporinida (family Enal loporidae), the Argentine basin was inhabited by the order Trepostomida (family Monticuliporidae). The second basin was probably warmwater, since it was located at 30° S. In the Baltic basin, in addition to the then existing families of the orders Cystoporida and Trepostomida, representatives of new families of the orders Trepostomida (Ralfimartitidae and Stenopo ridae) and Rhabdomisida (Goldfussitrypidae) appeared in the Early Volkhov time (Fig. 28). The Argentine and Baltic basins shared the family Monticuliporidae. Perhaps, its representatives appeared in the Argentine basin after their migration from the Baltic basin, where they were known earlier. Middle Volkhov Time. There are data on bryozoans from three basins: Avalonian, North American, and Baltic. In the Avalonian basin some representatives of the order Phylloporinida (family Enalloporidae) still persisted, in the North American, in addition to the bryozoans of the families Aisenvergiidae and Hal loporidae, representatives of two more families of the order Trepostomida persisted: Monticuliporidae and Stenoporidae. There are no data on bryozoans of the order Cystoporida for this time period. In the Baltic basin, new bryozoans appeared in addition to the pre viously known bryozoans belonging to the orders Cys toporida (family Revalotrypidae), Trepostomida (families Esthonioporidae, Halloporidae, Phrag moporidae, Monticuliporidae, Ralfimartitidae, Ste noporidae), and Rhabdomisida (family Goldfussitrypi dae). The order Trepostomida was enriched by repre sentatives of the families Aisenvergiidae and Anisotrypidae. In addition, bryozoans of two new

Fig. 27. Distribution of bryozoans in the Floian time (based on Ross, 1966; Taylor and Cope, 1987; Tuckey, 1990; Wilson et al., 1992; Taylor and Wilson, 1999; Taylor and Ernst, 2004; Xia et al., 2007, Xia et al., 2008 with modifications, including new data). Explanation: (1–3) orders: (1) Trepostomida, (2) Cystoporida, (3) Cryptostomida. PALEONTOLOGICAL JOURNAL

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KOROMYSLOVA Reva lotryp idae G ol df us sit ry pi da e

968

Dapingian (Early Volkhovian) time


Esthonioporidae

Siberia

Halloporidae

Taim yr

Phragmoporidae

Monticuliporidae

Kazakhstan

Monticuliporidae Ralfimartitidae

Ar


Tarim

South China

Perunica rica mo

Stenoporidae

13a Av alo nia

Lauren tia

Baltica

South Pole 15b 15a

Enalloporidae 60S Mexican Terrane

Gondwana

Revalo trypida e Pti lod icty ida e

30S

e da pi y r sit us df l o G ridae elopo Phac

Dapingian (Middle Volkhovian) time Aisenvergiidae Halloporidae Monticuliporidae Stenoporidae


Siberia

Aisenvergiidae Esthonioporidae Halloporidae Phragmoporidae

Taim yr

Kazakhstan

Monticuliporidae Ralfimartitidae Anisotrypidae Stenoporidae

ca Perunica ori Arm


Tarim

South China

13a Av alo nia

Laure ntia

Baltica

South Pole 15b 15a

Enalloporidae 60S Mexican Terrane

Gondwana

30S

Explanation 1

2

3

4

5

6


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2011


orders appeared: Cryptostomida (family Ptilodictyidae) and Tubuliporida (family Phaceloporidae) (Fig. 28). The North American and Baltic basins shared the families Aisenvergiidae, Halloporidae, Monticuli poridae, and Stenoporidae. It seems plausible that representatives of the family Monticuliporidae invaded the North American basin after their migra tion from the Argentine basin, and the Stenoporidae invaded from the Baltic basin. Bryozoans Aisenvergi idae appeared in the Baltic basin probably after their migration from the North American basin. It seems likely that in the Middle Volkhov time these basins were connected. Early Darriwilian Age Late Volkhov time. There are data on bryozoans from four basins: South Chinese, Avalonian, North American, and Baltic. The South Chinese basin was inhabited by bryozoans of the order Trepostomida (family Monticu liporidae), the Avalonian basin was inhabited by bryozo ans of the order Phylloporinida (family Enalloporidae), the North American basin was inhabited by bryozoans of two orders: Trepostomida (families Aisenvergiidae, Halloporidae, Monticuliporidae, Stenoporidae) and Cryptostomida (family Ptilodictyidae), the Baltic basin was inhabited by bryozoans of five orders: Cystoporida (family Revalotrypidae), Trepostomida (families Esthonioporidae, Aisenvergiidae, Halloporidae, Phragmoporidae, Monticuliporidae, Ralfimartitidae, Stenoporidae, Anisotrypidae), Rhabdomisida (family Goldfussitrypidae), Cryptostomida (family Ptilodicty idae), and Tubuliporida (family Phaceloporidae) (Fig. 29). The South Chinese, North American, and Baltic basins shared in that time the family Monticuli poridae, in addition, the North American and Baltic basins shared the families Aisenvergiidae, Hal loporidae, Stenoporidae, and Ptilodictyidae. Perhaps, bryozoans of the family Ptilodictyidae migrated from the Baltic basin to the North American basin; and those of the family Monticuliporidae, to the South Chinese basin. Based on the analysis of the paleogeographical dis tribution of the oldest bryozoans it would appear rea sonable that their most probable center of origin was the South China basin, from which the most ancient bryozoans of the orders Trepostomida and Cryptosto mida are known. Subsequently bryozoans became to invade the North American and Avalonian basins, and only as late as the midFloian age they migrated to the Baltoscandian basin. It is possible that this is due to the

969

sea level rise during the Early Ordovician (Floian) transgression and the eastward opening of the basin (in modern coordinates), in the direction of the Uralian paleoocean. The Baltic Basin is characterized by a larger diversity of bryozoans, perhaps because they are better studied. Apparently, from the Dapingian time onward it was the center of radiation of bryozoans. In general the early evolution of the main orders of Paleozoic bryozoans occurred during the Tremado cian–Dapingian time. Six out of eight bryozoan orders known from the Paleozoic appeared during that time. The taxonomic and morphological diversity of the oldest bryozoans suggests that this group could have appeared earlier. However, the oldest bryozoans Tre postomida and Cryptostomida have so far been known from the Tremadocian Stage of South China, reliable Cystoporida are known from the Floian Stage (Bill ingen subhorizon) of the Leningrad Region (Cysto porida from the Tremadocian Stage of North America are possibly older), Rhabdomesida are known from the Dapingian Stage (Volkhov Horizon, BIIα subhorizon) of Estonia, Tubuliporida are known from the Dapin gian Stage (Volkhov Horizon, BIIβ subhorizon) of the Leningrad Region, and Phylloporinida are known from the Dapingian Stage of Ireland. Figure 30 shows the emergence time of six orders of Paleozoic bryozoans. CONCLUSIONS The morphology of the Latorp and Volkhov bryo zoans of the orders Cystoporida and Trepostomida in the Leningrad Region have been studied. In general the Latorp and Early Volkhov bryozoans of the order Cystoporida are characterized by laminate or massive colonies mainly of hemispherical shape, the bryozo ans of the order Trepostomida are characterized by massive colonies of varying shapes. Among the Early Volkhov Cystoporida occur massive rodshaped colo nies with a flat slightly expanded base. The Middle Volkhov Cystoporida and Trepostomida have the same shapes of colonies that they have in the Early Volkhov time. In the Leningrad region the first occurrences of bryozoans of the orders Tubuliporida and Cryptosto mida are dated to the Middle Volkhov time. The Tubu liporida are characterized by recumbent and rod shaped colonies, and the Cryptostomida are charac terized by erect dendroid and fanlike forms with an extended encrusting base as well as ribbonlike colo nies. In the Late Volkhov time the representatives of all four orders continued to develop colonies of the same shapes as in the Middle Volkhov time. At the same time, the numbers and diversity of rodshaped and

Fig. 28. Distribution of bryozoans in the Dapingian time (based on data of Bassler, 1911; Modzalevskaya, 1953, 1986; Yang, 1957; Hinds, 1970; Dzik, 1981; Taylor and Curry, 1985; Gorjunova and Lavrentjeva, 1987, 1993; Gorjunova, 1988, 1996, 2005; Carrera, 1995; Taylor and Rozhnov, 1996; Wilson et al., 1992; Pushkin and Popov, 2001; Koromyslova, 2004b, 2007; Xia et al., 2008 with modifications, including new data). Explanation: (1–6) orders: (1) Trepostomida, (2) Cystoporida, (3) Cryptostomida, (4) Rhab domesida, (5) Tubuliporida, (6) Phylloporinida. PALEONTOLOGICAL JOURNAL

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KOROMYSLOVA Revalo trypida e Pti lod ict yid ae

970

Ptilodictyidae

Early Darriwilian (Late Volkhovian) time

us df ol dae G pori celo a h P

Aisenvergiidae Halloporidae Monticuliporidae Stenoporidae


Aisenvergiidae Esthonioporidae Halloporidae Phragmoporidae

Siberia Taim yr

Monticuliporidae Ralfimartitidae Anisotrypidae Stenoporidae

Kazakhstan Baltica

Enalloporidae

13a Av alo nia

Lauren tia


Tarim

South China

ca Perunica ori Arm

e da pi y r sit

South Pole

60S Mexican Terrane

Monticuliporidae

15b 15a

Gondwana

30S

Explanation 1

2

3

4

5

6

Fig. 29. Distribution of bryozoans in the Early Darriwilian time (based on data of Bassler, 1911; Modzalevskaya, 1953, 1986; Yang, 1957; Hinds, 1970; Dzik, 1981; Taylor and Curry, 1985; Gorjunova and Lavrentjeva, 1987, 1993; Gorjunova, 1988, 1996, 2005; Taylor and Rozhnov, 1996; Wilson et al., 1992; Pushkin and Popov, 2001; Koromyslova, 2004b, 2007 with modifications, including new data). Explanation: (1–6) orders: (1) Trepostomida, (2) Cystoporida, (3) Cryptostomida, (4) Rhabdomesida, (5) Tubuliporida, (6) Phylloporinida.

dendroid forms increased in bryozoans of the order Trepostomida. The shapes of bryozoan colonies inhabited the sea occupying the Leningrad region became most diverse in the MiddleLate Volkhov time, when dendroid and fanlike erect forms and rib bonlike, recumbent, and numerous rodshaped colo nies appeared. In bryozoans of the order Trepostomida acantho zooecialike structures with an internal cavity sur rounded by thin walls have been discovered. They dif fer from macroacanthozooecia sensu Astrova (1977) in the absence of a secondary strongly thickened wall and from styles in the presence of an internal cavity. The author refer to these structures as acanthozooecia

because there is not enough material for separating them as a new type of heterozooecia. The emergence time of all types of heterozooecia that were present in the colonies of the Latorp– Volkhov bryozoans has been determined more accu rately. It is possible that the oldest varieties of hetero zooecia are acanthozooecia and exilazooecia that appeared in the Tremadocian time. The earliest acan thozooecia have been observed in bryozoans Nekhoro sheviella and Orbiramus; and the earliest exilazooecia, in Orbiramus. Both of these genera were discovered in the Tremadocian of South China. In the Leningrad Region bryozoan colonies with acanthozooecia (Hemiphragma priscus) are known from the Floian

Explanation of Plate 23 Fig. 1. Anaphragma verectum Koromyslova, sp. nov.; paratype PIN, no. 5075/441; (1a) longitudinal section of the colony, ×10; (1b) cross section of the colony, ×10; (1c) cross section of the colony, ×10; (1d) cross section of the colony, ×10; (1e) tangential section of the colony, ×20; Leningrad Region, Volkhov River, village of Simankovo; Volkhov horizon, subhorizon BIIβ. PALEONTOLOGICAL JOURNAL

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971 Plate 23

1 mm 1b

1a

1 mm

1d 1 mm

1e

1c 1 mm


Vol. 45

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1 mm

972

KOROMYSLOVA Ordovician

System

Lower Ordovician Tremadocian

Floian

Tremadoc

Middle Ordovician Dapingian

Series

Darriwilian

Arenig

Stage Stage

Llanvirn Families Anisotrypidae Stenoporidae

GSS

Suborder Amplexoporina

Esthonioporidae

Trepostomida

ISS

Suborder Esthonioporina

Aisenvergiidae

Halloporidae Phragmoporidae

Suborder Halloporina

Monticuliporidae Ralfimartitidae

Cryptostomida Ptilodictyidae Suborder Ptilodictyna Intraporidae Suborder Intraporina

?Cystoporida Ceramoporidae

Suborder Revalotrypidae Ceramoporina

Rabdomesida Goldfussitrypidae

Suborder Goldfussitrypina

Tubuliporida Phaceloporidae

Suborder Paleotubuliporina

Phylloporinida Enalloporidae Explanation one genus PALEONTOLOGICAL JOURNAL

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Fig. 30. Distribution of bryozoan orders in the Lower and Middle Ordovician (Tremadocian–Darriwilian stages) (based on data of Bassler, 1911; Modzalevskaya, 1953, 1986; Yang, 1957; Ross, 1966; Hinds, 1970; McLeod, 1978; Dzik, 1981; Taylor and Curry, 1985; Taylor and Cope, 1987; Gorjunova and Lavrentjeva, 1987, 1993; Gorjunova, 1988, 1996, 2005; Taylor and Rozhnov, 1996; Tuckey, 1990; Wilson et al., 1992; Taylor and Wilson, 1999; Pushkin and Popov, 1999, 2001; Taylor and Ernst, 2004; Koromyslova, 2004b, 2007; Xia et al., 2007 with modifications, including new data).

time (Latorp) onward, and those with exilazooecia (Anaphragma vetustum) are known from the Dapin gian (early Volkhov). The youngest structures in the stratigraphic interval under consideration are neozoo ecia and mesozooecia of three types. Bryozoans with neozooecia and mesozooecia of the first and second types appeared in the Floian time, and bryozoans with moniliform mesozooecia appeared in the Dapingian time. The earliest occurrence of neozooecia has been recorded in bryozoans Revalotrypa from the Latorp of the Leningrad Region; that of mesozooecia of the first type, in Dianulites fastigiatus from the Floian of West ern Utah (in the Leningrad Region this species is known from the Lower Volkhov); that of mesozooecia of the second type, in Phragmopora lavaensis, Dit topora clavaeformis, D. annulata, and Hemiphragma priscum from the Latorp of the Leningrad Region; and that of moniliform mesozooecia, in Dianulites multi mesoporicus from the Middle Volkhov of the Leningrad Region. It has been established that the earliest occurrences of styles and vesicular tissue were recorded in bryozoan colonies from the Floian (Latorp) of the Leningrad Region: styles, in Esthonioporella miranda; vesicular tissue, in the genera Esthoniopora and Esthonioporella. The paper has provided diagnoses of three families based on new data supplementing and refining them: Revalotrypidae Gorjunova, 1986; Esthonioporidae Vinnassa de Regny, 1921; and Phragmoporidae Push kin, 1987. Nineteen species, including three new spe cies, belonging to ten genera have been described. In the Latorp and Volkhov horizons four bryozoan assemblages have been identified. The Latorp assem blage is represented by 13 species of seven genera, five families, three suborders, and two orders; the Lower Volkhov assemblage is represented by 19 species of eight genera, six families, four suborders, and two orders; the Middle Volkhov assemblage is represented by 30 species of 16 genera, ten families, six suborders, and four orders; the Upper Volkhov assemblage is rep resented by 36 species of 16 genera, ten families, six suborders, and four orders. Three stages in the development of bryozoans have been established: Latorp, Early Volkhov, and Middle– Late Volkhov. The transition from the Early to the Middle Volkhov time was the most significant period in the development of bryozoans of the Baltic Basin. In the Middle Volkhov time representatives of two new orders, two suborders, four families, seven genera, and 11 species appeared in the basin, the shape of colonies became more diverse, and the serial and bilateral body plans of colonies formed. PALEONTOLOGICAL JOURNAL

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Based on the analysis of the paleogeographical dis tribution of the oldest bryozoans it would appear rea sonable that their most probable center of origin was the South China basin, from which the most ancient bryozoans of the orders Trepostomida and Cryptosto mida are known. Subsequently bryozoans became to invade the North American and Avalonian basins, and only as late as the midFloian age they migrated to the Baltoscandian basin. It is possible that this is due to the sea level rise during the Early Ordovician (Floian) transgression and the eastward opening of the basin (in modern coordinates), in the direction of the Uralian paleoocean. The Baltic basin is characterized by a larger diversity of bryozoans, perhaps because they are better studied. Apparently, from the Dapingian time onward it was the center of radiation of bryozoans. In general the early evolution of main orders of Paleozoic bryozoans occurred in the Tremadocian– Dapingian time. Six out of eight bryozoan orders known from the Paleozoic appeared during that time. orders of bryozoans from eight known in the Paleo zoic. The taxonomic and morphological diversity of the oldest bryozoans suggests that this group could have appeared even earlier. However, the oldest bryo zoans of Trepostomida and Cryptostomida have so far been known from the Tremadocian Stage of South China, reliable Cystoporida are known from the Floian Stage (Billingen subhorizon) of the Leningrad Region, (Cystoporida from the Tremadocian Stage of North America are possibly older), Rhabdomesida are known from the Dapingian Stage (Volkhov Horizon, BIIα subhorizon) of Estonia, Tubuliporida are known from the Dapingian Stage (Volkhov Horizon, BIIβ sub horizon) of the Leningrad Region, and Phylloporinida are known from the Dapingian Stage of Ireland. It seems plausible that the environmental condi tions in the Tremadocian–Early Darriwilian time (Early Ordovician–first half of the Middle Ordovi cian) were more favorable for representatives of the order Trepostomida than for the other orders. This is evidenced by the diversity of colony shapes, the pres ence of different types of the autozooecial apertures from rounded polygonal to petaloid, and the presence of almost all kinds of heterozooecia known in Trepos tomida throughout the Paleozoic. In addition, the abundance of diaphragms and alternating hemi phragms in colonies of Trepostomida is evidence of the wide distribution of the second mode of regeneration, which is related to the unstable position of polypides. Thus, the stable and unstable positions of polypides, which could exist due to these two modes of regenera tion, provided some advantages for bryozoans of Tre

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1b 1 mm 1a

1с

1 mm

1 mm

1 mm

2

Explanation of Plate 24 Figs. 1 and 2. Anaphragma verectum Koromyslova, sp. nov.; (1) paratype PIN, no. 5075/440; (1a) longitudinal section of the col ony, ×10; (1b) cross section of the colony, ×10; (1c) tangential section of the colony, ×20; Leningrad Region, Volkhov River, village of Simankovo; Volkhov horizon, subhorizon BIIβ; (2) paratype PIN, no. 5075/439; longitudinal section of the colony, ×5; the same age and location.

postomida, while Cystoporida possessed only one mode of regeneration, related to the stable position of polypides. It seems likely that the unstable position of

polypides that began to prevail in Trepostomida in the early Volkhov facilitated the rapid growth of colonies. In addition to the welldeveloped morphology, the PALEONTOLOGICAL JOURNAL

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flourishing of this group of bryozoans is evidenced by their taxonomic diversity and domination in the assemblages studied. ACKNOWLEDGMENTS The author is grateful to R.V. Gorjunova, A.S. Ale kseev, L.A. Viskova, O.B. Bondarenko, O.B. Weiss, S.V. Rozhnov, L.I. Kononova, and I.S. Barskov for helpful discussions and valuable advice, to A.A. Madi son, S.V. Rozhnov, P.V. Fedorov, and V.B. Ershova for the material, to M.M. Key Jr. and A. Ernst (Germany) for the literature, to P.D. Taylor (Great Britain) for information on the type specimens of the species of the genera Orbipora and Esthoniopora, and to V.I. Sidorkin, A.V. Mazin, and P.B. Kabanov for aid in preparation of thin sections and photographs. REFERENCES Alikhova, T.N., Rukovodyashchaya fauna brakhiopod ordo vikskikh otlozhenii severozapadnoi chasti Russkoi platformy (Index Brachiopod Fauna of the Ordovician of the North western Russian Platform), Moscow: Gos. Izd. Geol. Lit., 1953, pp. 3–22. Antoshkina, A.I., Rifoobrazovanie v paleozoe (sever Urala i sopredel’nye oblasti) (Reef Formation in the Paleozoic (Northern Urals and Adjacent Areas)), Yekaterinburg: Ural’sk. Otdelen. Ross. Akad. Nauk, 2003. Astrova, G.G., Lower Silurian Trepostomata of the Kozhima River, Ezheg. Vseross. Paleontol. Obva, 1945, vol. 12, pp. 81–92 (1945). Astrova, G.G., Lower Silurian Trepostomata of the Pay Khoy Range, Uch. Zap. Mosk. Ped. Inst., 1948, vol. 52, no. 3, pp. 3–35. Astrova, G.G., First Records of Lower Silurian Treposto matous Bryozoans from Siberia, Tr. Mosk. Obva Ispyt. Prir., Otd. Geol., 1951, vol. 1, pp. 128–135. Astrova, G.G., On Generic Assemblages of Bryozoans from Silurian Deposits of the Soviet Union, Byull. Mosk. Obva Ispyt. Prir., Otd. Geol., 1955, vol. 60 (vol. 30), no. 3, pp. 57–73. Astrova, G.G., On the Systematic Position of Bryozoans Diplotrypa and Monotrypa, Materialy k osnovam paleon tologii (Materials to the Fundamentals of Paleontology), Moscow: Paleontol. Inst. Akad. Nauk SSSR, 1958, no. 2, pp. 3–6. Astrova, G.G., Siluriiskie mshanki Tsentral’noi i Zapadnoi Tuvy. Tr. Paleontol. Inst. Akad. Nauk SSSR. T. 79 (Silurian Bryozoans of Central and Western Tuva: Proceedings of the Paleontological Institute of the Academy of Sciences of the USSR, Vol. 79), Moscow: Nauka, 1959. Astrova, G.G., Stratigraphic Distribution of Bryozoans in the Ordovician and Silurian of the USSR and North Amer ica, Stratigrafiya i korrelyatsiya ordovika i silura. Mezhdu nar. Geol. Kongress, XXI sessiya, Doklady sovetskikh geol ogov, problema 7 (Stratigraphy and Correlation of the Ordovician and Silurian. Int. Geol. Congress, XXI Session, Reports of Soviet Geologists, Problem 7), Leningrad: Gostoptekhizdat, 1960a, pp. 136–153. Astrova, G.G., Order Trepostomata, Osnovy paleontologii. Spravochnik dlya paleontologov i geologov SSSR. Mshanki, PALEONTOLOGICAL JOURNAL

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Reviewed by L.A. Nevesskaja, Doctor in Biology


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