Ordovician (Billingen and Volkhov Stages) Brachiopod Faunas of the East Baltic

Eva Egerquist

Ordovician (Billingen and Volkhov stages) brachiopod faunas of the East Baltic

1 Dissertation presented at Uppsala University to be publicly examined in Lecture Theatre, Palaeontology building, Uppsala, Friday, June 4, 2004 at 13.00 for the degree of Doctor of Philosophy. The examination will be conducted in English.

Abstract Egerquist E. 2004. Ordovician (Billingen and Volkhov stages) brachiopod faunas of the East Baltic. 34 pp. Uppsala. ISBN 91-506-1756-7

Lower-Middle Ordovician (Arenig) successions in the East Baltic have been investigated for more than one hundred and fifty years. Nevertheless detailed sampling still yields new species and better knowledge of the environment in which these organisms lived. The successions are well suited for bed by bed sampling because of the lack of tectonic disturbance and because the sequences are well documented. This study analyses collections of Billingen-Volkhov age mainly from the St. Petersburg region, but also from Estonia. A great deal of the material was obtained from the marly to clayey, soft sediment that intercalates the compact packstones and wackestones in the succession. Twenty-nine of these clay horizons were used for diversity estimates on the fauna through the succession. The most thoroughly investigated groups for this investigation were rhynchonelliformean brachiopods, conodonts and ostracodes. The results indicate that variances in diversity and abundance levels for these groups were not correlated, either to each other or to the small-scale sea level fluctuations that have been suggested for the region. However, diversity dynamics of brachiopods and ostracodes confirm the large-scale upward shallowing of the basin into the Upper Volkhov. Comparison with fossils from the limestones did not reveal any differences in faunal composition between the two preservation modes. The detailed sampling, coupled with sampling of the recently described mud mounds that occur in several outcrops, yielded large numbers of specimens. This enabled revision of earlier poorly known rhynchonelliformean genera such as Ujukella Andreev, as well as better known genera such as Porambonites Pander. In total the examined faunas include 31 genera assigned to 53 species of rhynchonelliformean brachiopods. Of these Leoniorthis and Eoporambonites are defined as new genera, and the following new species are described: Neumania paucicostata, Ranorthis rotunda, Orthidium gambolovensis, Orthidium lavensis, Skenidioides minutus, Tetralobula peregrina, Idiostrophia prima and Idiostrophia tenuicostata.

Keywords: Early Middle Ordovician, Billingen Regional Stage, Volkhov Regional Stage, Diversity, Brachiopoda, Conodonta, Ostracoda, Estonia, Russia.

Eva Egerquist, Department of Earth Sciences, Palaeobiology, Norbyvägen 22, SE-752 36 Uppsala, Sweden.

DISCLAIMER This manuscript is produced only for public examination as a doctoral thesis. It is not a publication in the sense of the international Code of Zoological Nomenclature.

ISBN 91-506-1756-7

Printed in Sweden by Geotryckeriet, Uppsala 2004

2 List of Papers

I Tolmacheva, T., Egerquist, E. Meidla, T. and Holmer, L. 2001. Spatial variations in faunal composition, Middle Ordovician, Volkhov Stage, East Baltic. GFF 123 pp. 65-72.

II Tolmacheva, T., Egerquist, E. Meidla, T., Tinn, O. and Holmer, L. 2003. Faunal composition and dynamics in unconsolidated sediments: a case study from the Middle Ordovician of the East Baltic. Geological Magazine 140 (1) pp. 31 – 44.

III Tolmacheva T. Fedorov P. and Egerquist E. 2003. Conodonts and brachiopods from the Middle Ordovician microbial mud mound at Putilovo Quarry, north-western Russia. Bulletin of the Geological Society of Denmark, 50 (1) 63-74.

IV Egerquist, E. 2003. New brachiopods from the Lower-Middle Ordovician (Billingen-Volkhov stages) of the East Baltic. Acta Palaeontologica Polonica 48 (1) 31-38.

V Egerquist, E. 1999. Revision of the plectambonitoid brachiopod Ujukella Andreev and related genera. GFF 121 pp. 325-332.

VI Popov, L. E., Egerquist, E. and Zuykov, M. In press. Ordovician (Arenig to Caradoc) Syntrophiidine brachiopods from the East Baltic. Accepted for publication in Palaeontology.

VII Egerquist, E. Manuscript. Early-Middle Ordovician (Billingen – Volkhov stages) orthid and protorthid brachiopods from East Baltic.

Reproduction of papers I-V was made with permission of the copyright holder. Paper I © 1999 by the Geological Society of Sweden, Stockholm. Paper II © 2003 by Cambridge University Press, Cambridge. Paper III © 2003 by the Geological Society of Denmark, Copenhagen. Paper IV © 2003 by Instityut Paleobiologii PAN, Warsaw. Paper V © 2001 by the Geological Society of Sweden, Stockholm.

Authorship statement In addition to contributing to the research and participating in the general preparation of the articles where more than one author is involved, I have been responsible for descriptions, numerical data and calculations on rhynchonelliformean brachiopods discussed in articles I, II and III.

3 4 Contents

Ordoviciska brachiopodfaunor från St. Petersburgområdet och Estland ...... 7 Material och undersökningsområde...... 7 Tidig och mellanordovicisk sedimentation i Östersjöområdet ...... 7 Paleogeografi och miljö...... 8 Brachiopodfaunans diversitet ...... 8 Den “trumpetande” brachiopoden ...... 9 Introduction...... 11 Research area and localities...... 11 Geological background...... 12 Brachiopod diversity...... 13 The Billingen brachiopod fauna ...... 15 The Volkhov brachiopod fauna ...... 15 Some aspects on the development of the delthyrial cover in Antigonambonites...... 19 Summary of papers...... 21 Sample size and fidelity of calculations ...... 21 Diversity and faunal dynamics ...... 21 Mud mound faunas ...... 22 Leoniorthis robusta and Neumania paucicostata ...... 22 Revision of the brachiopod Ujukella and related genera...... 22 Syntrophidiine brachiopods from Early and Middle Ordovician ...... 23 Orthid and protorthid brachiopods of Billingen and Volkhov age ...... 23 Acknowledgements...... 23 References ...... 24 Plate 1 ...... 26 Plate 2 ...... 28 Plate 3 ...... 30 Plate 4 ...... 32 Plate 5 ...... 34

5 6 Ordoviciska brachiopodfaunor från St. Petersburgområdet och Estland

Brachiopoder (armfotingar) är en i dag relativt ovanlig djurgrupp. Under paleozoikum var den däremot både artrik och vanlig. Denna avhandling behandlar de kalkskaliga (Rhynchonelliforma) brachiopodfau- nor som man hittar rester av i Estland och västra Ryssland i lager från tidig till mellanordovicisk ålder (billingen- och volkhovetagen för c:a 475-485 miljoner år sedan). De ordoviciska lagren i Baltikum och västra Ryssland är väl undersökta, allt ifrån den fossila faunan till tolkningar av den miljö där de olika sedimenten har avsatts. Ändå finns mycket kvar att upptäcka, till stor del tack vare de tektoniskt ostörda sedimenten och de ofta mycket välbevarade fossila lämningarna.

Material och undersökningsområde Materialet till avhandlingen kommer från ett flertal lokaler i området mellan Tallinn i Estland och floden Lynna i nordvästra Ryssland (Fig. 1). Alla dessa lokaler ligger utmed en kalkstensklint, kallad ”the Bal- tic-Ladoga Klint”, som sträcker sig längs Estlands hela norra kust, in i Ryssland till södra kanten av La- doga (Fig. 4). De plant liggande lagren är ofta lätt urskiljbara och enskilda lager går i vissa fall att spåra tiotals mil. De hårda sedimenten utgörs mestadels av märglig kalksten med inslag av glaukonit, framför- allt i de lägre lagren. Mellan kalkstenslagren finns ofta lösa ler- och siltavlagringar insprängda särskilt i volkhovlagren i S:t Petersburgområdet. En stor del av materialet till avhandlingen kommer just från dessa ler/siltavlagringar.

Tidig och mellanordovicisk sedimentation i Östersjöområdet Under ordovicium var stora delar av landområdena kring Östersjön och i Ryssland täckta av ett förhållan- devis grunt epikontinentalhav tillhörande den dåvarande kontinenten Baltica, som vid denna tid omfattade större delen av Skandinavien, Ryssland och nordöstra Centraleuropa. Det dåvarande grundhavet har inde- lats i olika så kallade konfaciesbälten (Jaanusson, 1982), vilka representerar olika djup och sedimenta- tionsförhållanden (Fig. 4). Det i den här avhandlingen behandlade området tillhör det nordestniska konfa- ciesbältet och anses tillhöra den grundare delen av bassängen. Under sen kambrium till tidig tremadoc avsattes här huvudsakligen sandiga till finklastiska sediment, följt av avsättning av ler- och kalkavlagringar, där det terrigena inslaget var litet. Lagerföljden i den därpå följande arenigepoken utgörs huvudsakligen av kalkstenar med silt/lerinslag, mellan vilka lösa siltiga - leriga sediment är insprängda. Sedimentationen har varit ytterligt långsam, med kanske bara några få millimeter under tusen år (Jaanusson, 1982) (Fig. 5).

7 Paleogeografi och miljö Under den första halvan av ordovicium låg undersökningsområdet på ungefär 40-50 grader sydlig bredd i ett troligen tempererat klimat (Fig. 3). Ett flertal försök har gjorts att bedöma temperaturen i det grundhav som omgav kontinenten, bland annat genom att mäta olika syreisotoper i fossil kalk. Dessa mätningar har dock givit skiftande resultat, från +8oC till runt +20oC (t. ex. Lindström, 1984; Dorofeeva et al. 1997). Djupet i bassängen har fluktuerat väsentligt över den tidsrymd som omspänns av billingen- och volkhovetagen. Under billingen blev havet successivt grundare, något som kulminerade i och med bildandet av en enormt utbredd och lätt igenkännlig diskontinuitetsyta. Denna har i Ryssland fått namnet ”Steklo” av lokala stenhuggare, medan den i Sverige kallas ”Blommiga bladet”. Härefter inleds volkhovetaget med en transgression, som med smärre fluktuationer varar till slutet av detta etage, där vattendjupet återigen sjun- ker drastiskt och en ny diskontinuitetsyta bildas vid gränsen mellan volkhov och kunda (Dronov et al 2003) (Fig. 5). En stor del av de bioklastiska kalkstenarna, som bildades i volkhov, har föreslagits vara så kallade tem- pestiter, vilka avlagrats vid extrema stormar. De lösa mellanliggande sedimenten skulle däremot vara avsatta under lugnare förhållanden (Dronov & Fedorov 1995; Dronov 1998). Enligt denna teori borde vattendjupet i bassängen ha legat någonstans mellan vågbasen för extrema stormvågor och den för normala stormvågor. Med tanke på det förmodat öppna läget mot väster, och att vindarna troligen var västliga på dessa breddgrader under ordovicium liksom idag, så kan en försiktig uppskattning av djupet röra sig mellan sextio och hundra meter. De fossila lämningarna av den fauna som levde på dessa lugna, svagt sluttande mjukbottnar, utgörs vo- lymmässigt huvudsakligen av brachiopoder. Tillsammans med dessa hittar man också ostrakoder, bryozo- er, tagghudingar, snäckor, conodonter och machaerider.

Brachiopodfaunans diversitet Den fossila brachiopodfaunan genomgår en markant förändring vid det sedimentationsavbrott som utgör gränsen mellan billingen och volkhov (Fig. 5). I materialet från billingen har 19 olika släkten hittats. Av dessa har 10 försvunnit i volkhov, där de i stället ersätts av 12 nya, så att det totala antalet släkten i detta etage uppgår till 21. I billingen tillhör 53% av släktena (10 st.) ordningen Orthida, medan pentamerider, billingsellider och plectambonitider vardera representeras av 4, 3 och 2 släkten. Av de 21 släktena i volkhov däremot, tillhör endast 38% orthiderna. Ordningen Protorthida introduceras med ett släkte, pentamerider och plectambonitider representeras av 2 släkten vardera, medan billingselliderna har ökat i antal så att de nu är lika diversifierade som orthiderna med 38% av släktena. Orthidernas relativa dominans tyder på att vattentemperaturen var relativt låg snarare än den höga temperatur som vissa av resultaten från syreisotopmätningarna pekar på(Benedetto, 2001). Den lägre dominansen av orthider i volkhov beror på diversifieringen av de för Baltica typiska clitambonitiderna, därför är dessa värden troligen inte jämförba- ra med värden från andra områden. Det är värt att notera att ett flertal släkten, så som orthiderna Apheo- orthina, Prantlina, Orthidium och Angusticardinia, liksom även Tetralobula, försvinner redan en tid före övergången från billingen till volkhov, medan andra som Plectella och Panderina, försvinner vid eller strax ovanför sedimentationsuppehållet. Detta sammanfaller med den föreslagna snabba regression som påbörjades i övre delen av billingen, och vars maximum utmärks av den redan omtalade diskontinuitets- ytan Steklo (Fig. 5). Relativt snart efter att den efterföljande transgressionen hade inletts, invandrade ett antal nya släkten till området. En del av dem tycks ha varit ganska kortlivade och försvann nära gränsen mellan de traditionella epokerna dikari och zheltjaki. Vid denna tid sammanträffar en ny snabb transgression med uppträdandet av en andra grupp nykomlingar, så som Ingria, Gonambonites, Apomatella och djupvattensbrachiopoden Skenidioides. Skenidioides uppträder talrikt i några få prover från zheltiakiepo- ken, men avtar sedan och försvinner igen i den grundare översta delen av volkhov.

8 Den “trumpetande” brachiopoden Utformningen av den platta som skyddar pedikelöppningen hos clitambonitiderna, anses vara av betydel- se för klassifikationen av denna grupp. Plattan kan betecknas antingen som ett deltidium eller som ett pseudodeltidium, beroende på hur den har bildats. Detta diskuterades av A. Wright and M. Rubel (1996), vilka ansåg den vara ett deltidium, som bildats av två plattor som växte in mot mittlinjen ifrån pedike- löppningens kanter. De påpekade emellertid att man ännu inte kunnat fastställa hur den skall klassificeras hos släktet Anti- gonambonites, eftersom man hittat så få juvenila individer av detta släkte. Ett flertal små exemplar, som hittats i material från ansamlingar av finsediment, de flesta från den så kallade ”Sablino mud mound” vid floden Tosna, tyder på att det hos Antigonambonites inte rör sig om ett deltidium. De juvenila exempla- ren har en tydlig pedikelöppning omgiven av en trumpetformad pedikeltub (Fig. 7 & 9: 1-3). Tuben tycks till en början vara mer eller mindre fri från resten av skalet, men växte tidigt ihop med detta, även öpp- ningen tillslöts på ett tidigt stadium (Fig. 8). Även hos vuxna individer går det att spåra rester av bild- ningen. Nedre bilden i figur 8 visar ett itusågat och polerat vuxet exemplar, där gränsen mellan pedikeltu- ben och skalets ventralsida är tydligt skönjbar.

9 10 Introduction

Early-Middle Ordovician (Arenig) successions in the East Baltic region have been investigated for more than one hundred and fifty years. Nevertheless detailed sampling of, especially the soft, clayey sediments in the succession, still yields new species and better knowledge of the environment in which these organisms lived. The successions are well suited for bed by bed sampling because of the lack of tectonic disturbance (Fig. 1) and because they are well-documented (e.g. Dronov et al. 2000).

Research area and localities This work mainly deals with rhynchonelliformean brachiopod faunas from the Billingen and Volkhov stages. The material comes from several localities in the vicinity of St. Petersburg in Russia and from two localities in Tallinn, Estonia (Fig. 2) The Volkhov Stage material is mostly based on bed by bed sampling of the unconsolidated sediments at the Putilovo quarry and detailed sampling from a large mud mound from the same locality. All sampled localities are within the outcrop area of the so-called Baltic – Ladoga Klint, a more than 350 km long escarpment with numerous exposures of Ordovician deposits in the East Baltic area.

Figure 1. Frizy Unit at Putilovo quarry, showing the undisturbed horizontal layers in the succession.

11 Figure 2. Localities along the Baltic-Ladoga Klint, from which fossil material for this thesis was obtained. 1: Suhkrumägi and Harku trench; 2: Popovka river; 3: Tosna river with Sablino mud mound; 4: Putilovo quarry; 5: Lava river; 6: Volkhov river with Babino quarry; 7: Lynna and Syas rivers.

Geological background Lowermost Middle Ordovician deposits in Baltoscandia are characterised by very slow intermittent sedimentation in a rather shallow epicontinental sea, located within the temperate climatic zone (Jaanusson, 1973). The eastern part of the basin was characterised by predominantly siliciclastic deposition during the late Cambrian and early Tremadoc, followed by the formation of fine-grained argillites and carbonate deposits in the late Tremadoc to early Arenig. Continuous sedimentation of siliciclastic-starved carbonate sediments prevailed in the basin from the mid Arenig onwards. The Arenig succession is exposed continuously along the Baltic-Ladoga Klint, an erosional cliff, which extends from Lake Ladoga in north-western Russia and along the northern coast of Estonia (Fig. 1). The deposits along the Klint are, spatially, remarkably homogenous and undisturbed and consist of horizontal, easily recognizable units of calcareous packstones and wackestones alternating with soft silt/clay horizons. It is one of the best-documented successions in Baltoscandia (e.g. Dronov et al., 2000). The boundary between the Billingen and Volkhov regional stages is marked by a distinct hardground surface ("Steklo") which it is also possible to trace into Sweden, where it is known under the local name “Blommiga bladet”. In addition to the standard section several mud mounds of different size are found in some of the outcrops. These are, more or less circular, probably sponge mediated, build-ups consisting of thick clay lenses which are covered by micritic crusts (Fedorov 2003). In Putilovo quarry a large mud mound sits upon the Steklo surface and the lower clay lens is within the Baltoniodus triangularis conodont Biozone, which is otherwise missing in this outcrop (Fedorov and Dronov, 1998; Tolmacheva, Fedorov & Egerquist, 2003, Paper III).

Figure 3. Palaeomap showing Late Tremadoc-Early Arenig reconstruction (480-490 Ma). NCB = North China Block, SCB = South China Block, AV = Avalonia, AR = European Massifs, including the Armorican, Iberian and Bohemian Massifs. After Torsvik, 1998.

12 Palaeoenvironment During the Early-Middle Ordovician the research area was covered by a shallow epicontinental sea, and positioned approximately 40 - 50 degrees south of the equator on the palaeocontinent Baltica (e.g. Torsvik et al. 1998), (Fig.3). The continent was, rather rapidly, moving northwards, and probably experienced a temperate climate. However, several attempts to estimate water temperature using į18O measurements on different carbonate sources have yielded a wide range of data from +8oC annual surface water temperature (Lindström 1984) to values around +20 degrees (e.g. Dorofeeva et al. 1997). The deposits along the Baltic-Ladoga Klint belong to the North Estonian confacies belt (Fig. 4) which is considered to be the shallowest part of the basin (Jaanusson, 1982), with the most shallow part in Estonia and slightly deepening towards the eastern part of the klint. The water depth has undergone quite extensive fluctuations during the Billingen-Volkhov time span. During the Billingenian the sea became successively shallower, which culminated at the sequence boundary with the “Steklo” hardground surface. The Volkhov Stage is regarded as a transgressive episode, with a complete cycle of relative sea- level changes forming a well developed depositional sequence, shallowing again in the upper part to form a new erosionally truncated surface at the Volkhovian/Kundan boundary (Dronov et al, 2003), (Fig. 5). The depth in the basin is another matter of discussion. It has been suggested that a significant part of the bioclastic limestones in the Volkhov Stage represents proximal tempestites, deposited during major storm events somewhat below the seasonal storm wave base, whereas the soft silt/clay beds represent background deposits (e.g. Dronov 1999). According to this model an estimated depth of the basin should range between normal storm wave base and extraordinary storm wave base. Reconstructions of the palaeo-continent show a vast epicontinental sea facing southwest and probably exposed to a west-wind drift and quite extraordinary waves even at normal storms. If there were no sheltering island arcs, the waves could probably grow as high as 10 meters and as long as 150 to 200 meters. Calculating the wave base to approximately half the wavelength the estimated depth in the basin is likely to fall within at least 60-100 meters. The fossil remains of the fauna, which inhabited these predominantly calm and gently sloping shelves, is volumetrically dominated by a moderately diverse brachiopod assemblage, together with ostracodes, echinoderms, bryozoans, gastropods, conodonts and machaeridians (Tolmacheva et al. 2003, Paper II).

Figure 4. Map showing the approximate boundaries of Ordovician confacies belts in the Baltoscandian region. The double line shows the extension of the Baltic- Ladoga Klint. After Jaanusson 1982.

Brachiopod diversity The rhynchonelliformean brachiopods in this region show a marked shift at the sequence boundary between the Billingen and Volkhov stages (Fig. 5). In Billingen Stage 19 genera are present in the investigated samples. Of these 10 have disappeared in Volkhov, where, in stead 12 new genera appear so that the total number of genera in this stage is 21. In the Billingen assemblage 53% (10 genera) belong to the Order Orthida, whereas pentamerids, billingsellids and plectambonitoids are represented by 4, 3 and 2 genera respectively. In Volkhov Stage the assemblage contains 21 genera, of which the orthids constitutes 38%.

13 The Order Protorthida is represented by a single genus, whilst the pentamerids and plectambonitoids are represented with two genera each and the billingsellids have increased their number so that they now are as diverse as the orthids with 38% of the genera. The relative orthid dominance indicates a cool water temperature rather than the high values obtained by some of the oxygen isotope investigations (Benedetto, 2001). The lower relative orthid dominance in the Volkhov stage is due to the diversification of the typical Baltic clitambonitoids and is probably not comparable with similar estimates from other regions.

Figure 5. Stratigraphic column of the Billingen – Volkhov succession in St. Petersburg region, also showing the distribution of found brachiopod genera and sea level curve. The dashed lines for Oslogonites and Platystrophia indicate very few, widely spaced finds. Legend: 1) Limestones with iron oolites; 2) Bioclastic wackestones and packstones; 3) Thalassinoides burrowing systems; 4) Marls; 5) Clays; 6) Quartz sandstones; 7) Quartz sandstones with scattered glauconite grains; 8) Black shales; 9) Hard ground surface with Trypanites-like borings; 10) Hardground with pencil-like borings; 11) Uneven hardground surface evolved from firmground; 12) “Steklo” hardground surface with Gastrochaenolites oelandicus borings; 13) Planolites and other trace fossils; 14) Bergaueria at the bottom surface of the beds. Modified after Dronov et al, 2003.

14 It is noteworthy that the decline of several genera, such as the new plectambonitoid genus as well as Prantlina, Orthidium and Angusticardinia, which starts somewhat before the end of the Billingenian, as well as Plectella and Panderina which disappear at or slightly above the sequence boundary, seem to coincide with the suggested rapid sea level fall that began in the upper part of the O. evae conodont Biozone, the maximum of which is marked by the Steklo discontinuity surface at the sequence boundary (Fig. 5). Soon after the subsequent transgression had started, a number of new genera migrated into the region, some of which were rather short lived and disappeared close to the boundary between the two traditional units Dikari and Zheltiaki. At this time a new rapid transgression occurred, coinciding with a second group of newcomers such as Ingria, Gonambonites, Apomatella and the deep-water brachiopod Skenidioides. Skenidioides is abundant in a few samples in the Zeltiaki Unit, but decreases and disappears again at the shallow upper part of the Frizy Unit. This turnover pattern is even more obvious when looking at species level (Fig. 6).

The Billingen brachiopod fauna Plates 1 & 2; fig. 6 The brachiopod fauna of the Billingen Regional Stage include at least 24 species referred to 19 genera (Fig. 6). The fauna is strongly dominated by orthids, which include 13 species. Billingsellids and pentamerids include 4 species each and the strophomenids 3 species. The strophomenids are represented by two genera: Plectella Lamansky and a new, not yet published, genus. Plectella is morphologically very homogenous; however, there are three different distinctive shell ornamentations, probably indicating that they represent different species or subspecies (Plate I: fig. 1 A-F). The new genus was found at three localities, Volkhov, Tosna and Syas rivers, in lowermost Dikari Member (Oepikodes evae conodont Biozone). It is a moderately large, on average 6.5 mm wide and 5.5 mm long, concavo-convex and semicircular plectambonitoid, with short dental plates, simple cardinal process, low platform and no side septa. The ornament is unequally costellate. (Plate I: fig. 2 A-D). The pentamerids are represented by Tetralobula peregrina sp. nov., Idiostrophia prima sp. nov., Eoporambonites latus (Pander) and Porambonites intermedius Pander, all of which are discussed in paper VI. The billingsellids, not yet as diverse as in the following stage, are represented by three genera. Antigonambonites Öpik, and Neumania Harper, each with one species, are rather common, whereas Oslogonites Öpik only was found at one locality. Among the orthids Panderina is one of the most dominating genera. Several species of Panderina were described already in the nineteenth and early twentieth centuries; however, measurements on a large amount of specimens indicate that two of the described species, P. tetragonum (Pander) and P. lata (Pander) are junior synonyms to the type species Panderina abscissus (Pander) (Paper VII). Following this classification only P. abscissus is present in the material. Other dominating taxa are the dalmanelloid species Paurorthis resima (Rubel) as well as the plectorthoid genus Ranorthis Öpik, which is represented by three species including Ranorthis rotunda sp. nov. described here (Paper VII). Two new species of the wide spread genus Orthidium Hall & Clarke are also quite common in some samples. O. gambolovensis sp. nov. first occurs in the lowermost Mäekula Member and O. lavensis in lowermost Vassilkovo Member. They coexist until lower Dikari Member where they both disappear. Finally, I mention Leoniorthis robusta Egerquist which is sparsely present at a few levels in Vassilkovo Member but numerous in the mud mound at Putilovo quarry (upper Dikari Member). (Paper IV).

The Volkhov brachiopod fauna Plates 3, 4 & 5; fig.6 The brachiopod fauna of the Volkhov Regional Stage include at least 33 species distributed in 21 genera (Fig. 6). The fauna is dominated by the orders Orthida (14 species) and Billingsellida (13 species), whereas strophomenids and pentamerids are of minor importance. The strophomenids are represented by two plectambonitoid species; Ingria nefedyevi (Eichwald) is present from the P. originalis conodont Biozone and upwards, whereas the newly revised species Ujukella fastigata (Rubel) (paper V) first appears in the B. norrlandicus Biozone, where it is quite numerous especially in the upper part of the section.

15 16 17 Among the clitambonitidines the genus Neumania Harper is represented by two species: N. costata Pander and N. paucicostata Egerquist both of which are present already at the bottom of the Volkhov Stage. N. costata is quite rare, whereas N. paucicostata is present in most samples up to the Frizy Unit where it disappears. Apomatella ingrica (Pahlen) is the most frequent species of its genus; it appears in the lowermost Zheltiaki Unit and continues throughout the entire stage. A. secunda Öpik is much sparser and is present only in the Frizy Unit. Genera such as Lacunarites Öpik, Hemipronites Pander and Raunites Öpik are usually preserved as fragments only, which make their recognition somewhat difficult. However, the distinct ornamentation enables a fairly accurate classification. Lacunarites occurs throughout the Frizy Unit (B. norrlandicus Zone), whereas only one fragment referred to Hemipronites imbricata (Öpik) have been found in the upper part of this unit. Raunites is represented by four species: R. wolchowiana (Öpik), R. janischevskyi (Lesnikova), R. venusta (Öpik), and R. strophomenoides (Öpik). Among these R. wolchowiana is the most common species occurring throughout the Volkhov Stage, whereas R. strophomenoides is restricted to the Frizy Unit. From this unit comes one find of Oslogonites as well. A new species of the protorthid Skenidioides Schuchert & Cooper (Paper II) occurs first, with a few specimens, in the clay between beds 17 and 18 in the lower part of the Zheltiaki Unit (BIIE), large numbers occur in a clay horizon in bed 21, also BIIE. After that the genus decreases in abundance but reoccurs again in three clay horizons in the upper Frizy Unit. The orthids are represented by three superfamilies: Orthoidea Woodward, Plectorthoidea Schuchert & Le Vene, and Dalmanelloidea Schuchert. Among the orthoids Panderina Schuchert & Cooper, Glossorthis Öpik and Leoniorthis robusta (paper V) are restricted to the Dikari Unit (BIID), and have only been found in the large mud mound at the Putilovo Quarry (B triangularis and B. navis zones). Productorthis Kozlowski is represented by three approximately successive species: P. aculeata (Pander), P. obtusa (Pander) and P. parallela (Pander). Within the super family Plectorthoidea Ranorthis Öpik, and Nothorthis Ulrich & Cooper are the dominating genera throughout the whole Volkhov Stage, together with the dalmanelloid Paurorthis parva (Pander). Ranorthis is represented by three species, of which Ranorthis rotunda sp. nov. (paper VII) occurs in BIID and BIIE, whereas R. carinata Rubel and R. norvegica Öpik occurs in BIIE and BIIJ. A few fragmentary specimens of probable Platystrophia King were found in the Zheltiaki and Frizy units. Pentamerid brachiopods are represented by the genera Porambonites Pander and Idiostrophia Ulrich & Cooper, of which the latter occurs with two new species: I. tenuicostata sp. nov. and I. digitata sp. nov. (paper VI) in the upper part of the Frizy Unit. Porambonites is present in the Zheltiaki and Frizy units; it is mostly fragmentary which makes classification difficult, except for P. reticulatus Pander with its characteristic pitted pattern on the shell surface. However, the few complete specimens found, which do not belong to P. reticulatus, all belong to the species P. trigonus Pander, the shell surface of which is smooth. Thus probably the other smooth shell fragments also belong to this species, and they are tentatively classified as such in the range chart (Fig. 6).

18 Some aspects on the development of the delthyrial cover in Antigonambonites A large number of well-preserved juvenile shells of Antigonambonites can possibly shed some light on the enigmatic delthyrial cover in this genus. The development of the clitambonitidine delthyrial cover was discussed by A. Wright and M. Rubel (1996). They generally considered it as a deltidium that was formed by the deltidial plates and usually with a visible line of junction between them. However they point out that Antigonambonites is still problematic in this respect because of lack of evidence from juvenile specimens. Öpik (1934 p. 12, 151) mentions that the deltidium is perforated with a narrow foramen which is sealed already in young specimens and that the sealed knob probably served as a holdfast for young specimens. However he does not discuss the development of the structure. Juvenile and young specimens of Antigonambonites picked from soft sediment samples of volkhovian age, gives a hint of the development of the delthyrial cover in this genus. The material comes mainly from Sablino mud mound at Tosna river. The juveniles have a clearly visible pedicle foramen surrounded by a trumpet formed pedicle tube (Fig. 7 & 9: 1-3). This structure fuses quite early with the spondylium at the ventral side, and usually ends with a chevron formed tip. The posterior part, on the other hand, continues to grow as the interarea grows, the lateral edges underlying the edges of the delthyrium, and finally fusing to the sides of the spondylium (Fig. 8 & 9: 4).

Figure 7. Pedicle tubes on specimens PMU In 531 and PMU In 533.

Figure 8. Adult specimen PMU In 538 with marked deltyrial cover, damaged specimen PMU In 537 with visible suture between the delthyrial cover and the spondylium, and sectioned adult specimen PMU In 539 with visible sutures between the pseudodeltidium and the ventral valve.

19 The specimen on figure 9: 6 obviously died before the cover was completely fused with the spondylium. After death the compaction of the overlying sediment caused the two structures to separate, thus beautifully demonstrating the construction. The distal end of the tube is often differently shaped in different specimens, indicating that the tube was formed with the substrate, to which the larva was attached, as a template. When the brachiopod is about 5 to 6 mm wide, the pedicle foramen is already closed. However the distal surface of the tube still reflects the shape of the attached surface, although in many specimens there is a central pitch in it. It is difficult to say whether the brachiopod still was attached or not when the foramen was closed, with the sealed knob serving as a holdfast. However, the smooth and often well-preserved distal surface of the tube indicates that the brachiopods may have turned into a free lying mode of life already at this stage.

Figure 9. Pseudodeltidium in Antigonambonites. Scale bar 1 mm. 1-3: Juvenile specimens showing open pedicle tube. 1: PMU In 529; 2 A-B: PMU In 532; 3 A-C: PMU In 530; all from Sablino mud mound, Zheltiaki Member. 4: magnification of delthyrial cavity on adult specimen, showing the suture between the pseudodeltidium and the spondylium as described in the text, PMU In 538, Putilovo quarry, Frizy Member. 5: Specimen with loose pseudodeltidium, PMU In 536, Sablino mud mound, Zheltiaki Member. 6: Same specimen as on figure 8 without guidelines.

20 Summary of papers

Sample size and fidelity of calculations

Spatial variations in faunal composition, Middle Ordovician, Volkhov Stage, East Baltic. Tolmacheva, T., Egerquist, E. Meidla, T. and Holmer, L. 2001. GFF 123, pp. 65-72. (Paper I).

For this paper the easily recognised clay and marl horizons in Putilovo quarry were used for estimating the fidelity of calculations made on small sample size. Five clay beds were sampled and from each clay bed five samples of about the same size were taken in some distance from each other. All samples were treated in the same way: they were weighed, washed and then sieved into four fractions. The samples were then investigated on different criteria such as mineralogy, proportion of sediment fractions, degree of corrosion, amalgamation and fragmentation of the shell fragments, and composition of the faunal communities. Taxa investigated were brachiopods, ostracodes, conodonts, bryozoans and echinoderms. The investigation indicates that for quantitative palaeontological studies in the region, a sample size of about 200 specimens gives a relative error that is less than 10%. This error is less than the error related to the laboratory treatment of the samples of the same sizes, which is estimated to 12%, calculated on conodonts. Other conclusions that may be drawn from this investigation is that the relative error in the relative abundance of taxa that is connected with the small-scale spatial homogeneity is around 10 to 15%, that is to say that gradients in relative abundance of taxa, either lateral or vertical can be considered reliable if they exceed this value.

Diversity and faunal dynamics

Faunal composition and dynamics in unconsolidated sediments: a case study from the Middle Ordovician of the East Baltic. Tolmacheva, T., Egerquist, E. Meidla, T., Tinn, O. and Holmer, L. 2003. Geological Magazine 140 (1), pp. 31 – 44. (Paper II).

This study is an attempt to map the patterns of diversity and density of different taxa from Volkhov successions at Putilovo quarry. Although studies of fossil distribution patterns in a single section cannot discern the complete history of the original diversity of a region, some observations concerning the diversity and temporal dynamics of the palaeocommunities can be made. Twenty-nine clay horizons were investigated on six different organism groups, of which conodonts, brachiopods and ostracodes were the most thoroughly investigated taxa. Estimates made on each of these taxa were: density of fossil remains, species richness, and equitability (which quantifies whether the fauna is dominated by one or a few species or if the different species are evenly distributed in the assemblage). The diversity estimates from the clays were compared with estimates made on limestones from the same locality in order to discover possible differences between the two preservation modes. The limestones in this region have been interpreted as tempestite deposits by sedimentologists whereas the clays were interpreted as background sedimentation in shallow waters somewhat below normal storm wave base. However, there is no significant difference between the faunas in the limestone and clay beds, and there is no obvious size sorting, which does not correspond with such an interpretation.The three organism groups show no obvious correlation concerning the different estimates, which indicates that the community structure was not tightly integrated and that species responded to environmental changes according to their individual environmental tolerances. Furthermore, there is no obvious correlation between the small-scale variability in the diversity estimates and the suggested small-scale sea level curve for the region, which is supported by sedimentological and trilobite data. Thus, it may be suggested that the dominant elements in the studied palaeocommunity, like conodonts, brachiopods and ostracodes, were not sensitive to small scale sea level changes and other environmental changes of high frequency. However, diversity dynamics of brachiopods and ostracodes confirm the large-scale upward shallowing of the basin into the Upper Volkhov.

21 Mud mound faunas

Conodonts and brachiopods from the Middle Ordovician microbial mud mound at Putilovo Quarry, north- western Russia. Tolmacheva T. Fedorov P. and Egerquist E. 2003. Bulletin of the Geological Society of Denmark, 50 (1), 63-74. (Paper III).

Clay mounds are widely developed in the Lower Ordovician succession east of St. Petersburg (Russia) and are associated with a diverse and abundant fauna of brachiopods, ostracodes, conodonts, bryozoans and echinoderms. The lithology of one such mud mound in Putilovo quarry was previously studied, but not the faunas associated with the mound. The clay lenses in the Putilovo mud mound yield conodont assemblages belonging to the Baltoniodus triangularis and lowermost Paroistodus originalis conodont biozones, the stratigraphical intervals of which are much thicker than in the coeval Arenig successions lateral to the mound. The compositions of the conodont and brachiopod assemblages are generally the same in the mud mound as in contemporaneous beds. The occurrence of relatively fewer conodont elements in the mud mound than in the surrounding successions probably indicates the higher rate of accumulation of the mud mound clays. Juvenile brachiopods are more numerous in the clays of the mud mound than outside the build-up, supporting the hypothesis that the mounds included ecologically stressed environments.

Leoniorthis robusta and Neumania paucicostata

New Brachiopods from the Lower-Middle Ordovician (Billingen-Volkhov stages) of the East Baltic. Egerquist, E. 2003. Acta Palaeontologica Polonica 48 (1), 31-38. (Paper IV).

Two new rhynchonelliformean brachiopods, Leoniorthis robusta gen. et sp. nov. and Neumania paucicostata sp. nov., are described from the Billingen and Volkhov stages of the Baltic-Ladoga Klint area. All specimens were washed out from unconsolidated sediments that were sampled in Tallinn, Estonia and at three localities in St. Petersburg district, Russia. Numerous specimens were found in the large mud mound at Putilovo quarry, the lower part of which is within the Baltoniodus triangularis conodont Biozone, otherwise usually missing in this area. Leoniorthis robusta is more or less restricted to the mud mound, whereas Neumania paucicostata is common also in the clays higher up in the surrounding standard section. (Plate 3: fig. 3 A-C; Plate 4: fig. 1 A-D)

Revision of the brachiopod Ujukella and related genera

Revision of the plectambonitoid brachiopod Ujukella Andreev and related genera. Egerquist, E. 1999. GFF 121, pp. 325-332. (Paper V).

New material of the poorly known plectambonitoid brachiopod Ujukella fastigata (Rubel) is described from the Middle Ordovician (Upper Volkhov) of Lava river and Putilovo quarry, St. Petersburg district. To enhance comparison new descriptions are also provided for the closely related brachiopods Ujukella? geometrica (Kutorga) from slightly younger strata (Kunda Regional Stage) in the same region, for Ujukella sp. from contemporaneous deposits on Öland, Sweden, and for Ujukella alexandrae Andreev of Llanvirn age from Tuva, Siberia, close to the Kazakhstan border. M. Rubel, 1961 tentatively described two specimens from Lava river, with only exteriors preserved, as Eostrophomena? fastigata. The new specimens, which are externally very similar to Rubel´s specimens, but with several nicely preserved internal features, show that this brachiopod is not an orthid but a plectambonitoid, and thus can not be referred to the genus Eostrophomena. Furthermore, the close resemblance to the Siberian brachiopod Ujukella alexandrae shows that the two brachiopods belong to the same genus. A cladistic analysis based on 10 taxa and 20 characters supports this conclusion and indicates affinity to the Family Leptestiidae. (Plate 3: fig. 2A-D).

22 Syntrophidiine brachiopods from Early and Middle Ordovician

Ordovician (Arenig to Caradoc) Syntrophiidine brachiopods from the East Baltic. Popov L. E., Egerquist, E. and Zuykov, M. In press. Accepted for publication in Palaeontology. (Paper VI).

Syntrophiidine brachiopods are a rare and poorly known component of Ordovician faunas in Baltoscandia. In the East Baltic region they appear in the Billingenian (lower Arenig) as part of the earliest known benthic assemblages dominated by elements of the Palaeozoic Evolutionary Fauna. The fauna includes bryozoans, ostracodes, the earliest known porambonitoids, strophomenids and endopunctate orthids together with genera such as Idiostrophia and Orthidium which later became characteristic of the Whiterockian brachiopod assemblages in Laurentia, but by that time had completely disappeared from Baltica. The superfamily Syntrophioidea reappears in the Baltoscandia only in the mid Caradoc. By contrast, Porambonitoidea remained the integral part of the Baltoscandian brachiopod associations through the Ordovician. Porambonites, herein redefined on the basis of restudy of the type species P. intermedius, includes only smooth porambonitoids; taxa with distinctive ornament of radiating rows of pits first appeared in the group in the mid Arenig and are probably not congeneric with Porambonites. The taxa Eoporambonites gen. nov., Tetralobula peregrina sp. nov., Idiostrophia prima sp. nov. and Idiostrophia tenuicostata sp. nov. are newly established. (Plates 2 & 5).

Orthid and protorthid brachiopods of Billingen and Volkhov age

Early-Middle Ordovician (Billingen – Volkhov stages) orthid and protorthid brachiopods from East Baltic. Egerquist, E. Manuscript. (Paper VII).

Three new species of the orthid genera Orthidium Hall & Clarke, 1892 and Ranorthis Öpik, 1939 and one new species of the protorthid genus Skenidioides Schuchert & Cooper, 1931 are described from the Arenig succession (Billingen and Volkhov stages) of Estonia and north-western Russia. Detailed biometric study of an extensive material of Panderina Schuchert & Cooper, 1931, indicates that some of the earlier established species in reality represent intraspecific variants. Preliminary investigations of the genus Antigonambonites indicate a similar pattern. In contrast, other brachiopods, such as Orthidium and Skenidioides, group into more morphologically distinctive groups, and it would seem that the latter taxa mostly represent widespread or cosmopolitan forms. (Plates 1 & 4).

Acknowledgements John S. Peel is gratefully acknowledged for providing support and working facilities throughout this research at the Department of Earth Sciences (Palaeobiology), Uppsala University. He has also patiently read my manuscripts and improved my English. For comments on the language I also thank Michael G. Bassett (Cardiff) and Keith Bennett. My supervisor Lars Holmer is sincerely thanked for guidance without which I would have been lost in the jungle of names, rules, and formalities concerning these matters. I also thank Leonid Popov (Cardiff) who helped me a lot, especially with brachiopod classification. He has also, together with Andrei Dronov and Petr Fedorov (St. Petersburg), supplied me with additional material for this work. I am most grateful to Tatiana Tolmacheva (St. Petersburg), together with whom three of the papers included in this thesis are written, for many interesting and fruit bearing discussions. I also want to thank the rest of the staff within the Palaeontology building for providing support with various matters ranging from correcting proofs and translating Russian text to help with computer problems and preparation of fossil material. This work was supported by The Royal Swedish Academy of Sciences (KVA), the Swedish Research Council (VR), and Magnus Bergwall´s Foundation (to Lars Holmer) as well as by money from the Rector’s fund. Last, but not least, I want to acknowledge the staff at Rudbeckianska Gymnasiet, Västerås, who have provided me with a working schedule that enabled my work in Uppsala, and my family who has always encouraged and helped me.

23 References Benedetto, J. L. 2001. Palaeolatitudinal distribution patterns of higher rhynchonelliform brachiopods in the early Ordovician. In: Howard, C. Brunton, C. Cocks, L. R. M. & long, S. L (eds) Brachiopods Past and Present. The Systematic Association, London, Special Volume, Series 63, 299 – 314. Bruton, D. L. & Harper, D. A. T. 1981. Brachiopods and trilobites of the Early Ordovician serpentine Otta Conglomerate, south central Norway. Norsk Geologisk Tidskrift. 61, 153-181, pl. 1-5. Dorofeeva, L. A., Dronov, A. V., Prilutsky, R. E. & Pavlova, S. A. 1997. Sea-water temperature and salinity in the Volkhov (Lower Ordovician) palaeobasin in St. Petersburg region according to isotopic and geochemical data. In: T. N. Koren (ed), WOGOGOB Abstracts, St. Petersburg, 1997. pp.19, 20. Dronov, A. V. 1999. Sea level changes in the Lower Ordovician and their reflection in the tempestite sediments of the eastern part of the Glint. Bulletin of the Moscow Society of nature investigator Geology 74(4), 39-47 (in Russian). Dronov, A. V., Meidla, T., Ainsaar, L. & Tinn, O. 2000. The Billingen and Volkhov Stages in the Northern East Baltic: Detailed stratigraphy and lithofacies zonation. Proceedings of the Estonian Academy of Science, Geology. 49 (1), 3-16. Dronov, A. V., Koren, T. N., Tolmacheva, T., Holmer, L. & Meidla, T. 2003. ”Volkhovian” as a name for the third global stage of the Ordovician System. In: Albanesi, G. L., Beresi, M. S. and Peralta S. H. (Eds.). Ordovician from the Andes. Insuego, Serie Correlatión Geológica, 17, 59-40. Tucuman. Egerquist, E. 1999. Revision of the plectambonitoid brachiopod Ujukella Andreev and related genera. GFF 121, pp. 325-332. Eichwald, E. 1860. Lethaea Rossica ou Paléontologie de la Russie. 686 – 929, pls. 33-37. Stuttgart. Fedorov, P. V. 2003. Lower Ordovician mud mounds from the St. Petersburg Region, north-western Russia. Bulletin of the Geological Society of Denmark 50, 125-137. Fedorov, P. V. & Dronov A. V. 1998. Early Ordovician organic build-ups from nrth-western Russia. 1. Hecker-type mud mounds in Dikari member of Babino flagstone quarry. Vestnik Sankt- Peterburgskogo Universiteta, series 7: Geologia, Geographia 14, 81-87 (in Russian). Fedorov, P.V., Dronov, A.V. & Zavarzin, I.V. 1998. Early Ordovician organic buildups from north- western Russia. II. Hecker-type mud mounds in “Dikari “ member of Babino flagstone quarry. Vestnik Sankt Petersburgskogo Universiteta, Series 7: Geology, Geography. 14 27-36 (in Russian). Hall, J. & Clarke, J. M. 1892. An Introduction to the Study of the Genera of Paleozoic Brachiopoda. Natural History of New York, Paleontology, vol. 8, Part 1. Charles van Benthuysen & Sons. Albany. 367 p., 20 pl. Harper, D. A. T. 1981 See Bruton & Harper, 1981. Jaanusson, V. 1973. Aspects of carbonate sedimentation in the Ordovician of Baltoscandia. Lethaia 6, 11- 34. Oslo: Universitetsförlaget. Jaanusson, V. 1982. Introduction to the Ordovician of Sweden. In: Bruton, D. L. & Williams, S. H. (Eds.) Field excursion guide. IV International Symposium on the Ordovician System. Palaeontological Contributions from the University of Oslo 279, 1-10. King, W. 1850. A Monograph of the Permian Fossils of England. Palaeontographical Society Monograph, 3:xxxvii + 258 p., 29 pl. Kozlowski, R. 1927. Sur certains Orthides ordoviciens des environs de St. Petersburg. Bibliotheca Uni- versitatis Libirae Polonae Varsaviae. 17, 3-21, pl 1. Lesnikova, A. 1924. Palaeontologische Charakteristik des Untersilurs, zwischen den Stationen Swanka und Nasja, längs der Nord Bahn. Bulletin du Comité Géologique 42 (5-9), p. 153, pl. 4. Lindström, M. 1984. The Ordovician climate based on the study of carbonate rocks. In: Bruton, D. L. (Ed.) Aspects of the Ordovician System. Palaeontological Contributions from the University of Oslo 295, 81-88. Öpik, A. A. 1930. Brachiopoda Protremata der Estländischen Ordovizischen Kukruse-Stufe. Acta et Commentationes Universitatis Tartuensis, Tartu. 17, 1-261, pls. 1-22. Öpik, A. A. 1934. Über Klitamboniten. Acta et Commentationes Universitatis Tartuensis, Tartu. 26 1-190 pls. 1-48. Öpik, A. A. 1939. Brachiopoden und Ostracoden aus dem Expansusschiefer Norwegens. Norsk Geologisk Tidskrift 19, 117-142, fig.1-2, pls. 1-6. von der Pahlen, A. 1877. Monographie der Baltisch-Silurischen Arten der Brachiopodengattung Orthisina. Mémoires de l´Academie Imperiale des Sciences St. Petersbourg, series 7. 28 (8), 1-52.

24 Pander, C. H. 1830. Beiträge zur Geognosie des Russischen Reiches. Gedruckt bei K. Kray, St. Petersburg. xx + 165 p., 31 pl. Rubel, M. 1961. Lower Ordovician brachiopods of the superfamilies Orthacea, Dalmanellacea and Syntrophiacea of Eastern Baltic. ENSV Teaduste Academia Geologia Instituudi Uurimused VI, 141- 226, 27 pl. (In Russian). Rubel M. & Popov L. E. 1994. Brachiopods of the subfamily Atelelasmatinae (Clitambonitacea) from the Arenig, Ordovician, of the Baltic Klint Area. Proceedings of the Estonian Academy of Sciences, Geology. 43 (4),192-202. Schuchert C. & Cooper G. A. 1931. Synopsis of the brachiopod genera of the suborders Orthoidea and Pentameroidea, with notes on the Telotremata. American Journal of Science, series 5. 22, 241-255. Schuchert, C. & Le Vene, C. M. 1929. Brachiopoda (generum et genotyporum index et bibliographia). In: F. Pompeckj ed. Fossilium Catalogus, vol. 1, Animalia, Pars 42. Junk. Berlin. 140 p. Schuchert, C. 1913. Class Brachiopoda. The Lower Devonian deposits of Maryland. Maryland Geological Survey. Baltimore, p. 382. Tolmacheva, T., Egerquist, E. Meidla, T., Tinn, O. and Holmer, L. 2003. Faunal composition and dynamics in unconsolidated sediments: a case study from the Middle Ordovician of the East Baltic. Geological Magazine 140 (1), 31 – 44. Tolmacheva T. Fedorov P. and Egerquist E. 2003. Conodonts and brachiopods from the Middle Ordovician microbial mud mound at Putilovo Quarry, north-western Russia. Bulletin of the Geological Society of Denmark, 50 (1), 63-74. Torsvik, T. H. 1998. Palaeozoic palaeogeography: A North Atlantic viewpoint. GFF, 120, 109-118. Ulrich, E. O. & Cooper G. A. 1936. New genera and species of Ozarkian and Canadian brachiopods. Journal of Paleontology, 10, 616-631. Ulrich, E. O. & Cooper G. A. 1938. Ozarkian and Canadian Brachiopoda. Geological Society of America Special Papers. 13, 3223 p., 14 fig., 58 pl. Woodward, S. P. 1851-1856. A manual of the Mollusca. John Weale. London. 488 p., 24 pl. Wright, A. D. & Rubel, M. 1996. A review of the morphological features affecting the classification of clitambonitidine brachiopods. Palaeontology. 39, 53-75.

25 Plate 1 Scale bar 1 mm if nothing else is stated.

1. Plectella Lamansky. A, C & E showing different shell ornament. A & B: Plectella uncinata (Pander), ventral and dorsal view of conjoined specimen RM Br 137127, Popovka river, Mäekula member. C&D: Plectella sp. 1. external and internal of ventral valve showing shell ornament with striped pattern, PMU In 520. Popovka river, Vassolkovo Member. E: Plectella sp 2, external of ventral valve with “fishbone” pattern, RM Br 137186, Mäeküla, Estonia. Päite Member. F: Internal of dorsal valve, RM Br 137143, Tosna river, Vassilkovo Member. 2. New genus. A: dorsal exterior of conjoined specimen, PMU In 509, Syas river, lower Dikari Member. B: dorsal interior, Bc 13375, Mäekalda section, Estonia, probably Vassilkovo Member. C: ventral interior, RM Br 137185, Syas river, lower Dikari Member. D: ventral exterior showing shell ornament, RM Br 137181, Syas river, lower Dikari Member. 3. Prantlina incurvata (Lamansky). A: dorsal interior, PMU In 526, B: ventral exterior of conjoined specimen, PMU In 525, both specimens from Harku trench, Estonia, Mäekula Member. 4. Panderina abscissus (Pander). A: ventral exterior, PMU In 522, Volkhov river, Mäekula Member. B & C: exterior and interior of dorsal valve, PMU In 524, Volkhov river, Mäekula Member. 5. Orthidium lavensis sp. nov. A: interior of dorsal valve, holotype, PMU In 480, Popovka river, Vassolkovo Member. B: dorsal view of conjoined specimen, PMU In 483, Syas river, lower Dikari Member. 6. Orthidium gambolovensis sp. nov. A: interior of dorsal valve, holotype, PMU In 489, Sablino mud mound, Vassilkovo Member. B: exterior of ventral valve, PMU In 495, Popovka river, Mäekula Member.

26 27 Plate 2 Scale bar 1 mm if nothing else is stated.

1. Lycophoria lamanskii Rubel. Ventral view of conjoined specimen, PMU In 454, Babino quarry, Vassilkovo Member. 2. Angusticardinia recta (Pander). A & B: ventral and anterior views of conjoined specimen, PMU In 521, Harku trench, Estonia, Mäekula Member. 3. Ranorthis? trivia Rubel. A: ventral exterior, PMU In 96. B: dorsal interior, PMU In 97, both from Syas river, lower Dikari Member. 4. Neumania erecta (Pander). A: ventral view of conjoined specimen PMU In 527. B: lateral view of ventral valve, PMU In 528, both specimens from Volkhov river, Mäekula Member. 5. Porambonites intermedius (Pander). A-C: ventral, dorsal and anterior views of conjoined specimen, holotype, RM Br 137423, Lava river, Vassilkovo Member. 6. Tetralobula peregrina sp. nov. A & B: exterior and interior of dorsal valve, CNIGR 209/222, Volkhov river, loose sample. 7. Eoporambonites latus (Pander). A & B: ventral and anterior views of conjoined specimen, neotype, CNIGR 875/222, Popovka river, Mäekula Member. 8. Idiostrophia prima sp. nov. A-C: ventral, dorsal and lateral views of conjoined specimen, holotype, RM Br 137126, Popovka river, Vassilkovo Member.

28 29 Plate 3 Scale bar 1 mm if nothing else is stated.

1. Ingria nefedyevi (Eichwald). A: ventral exterior of conjoined specimen, PMU In 456, Lava River, Frizy Unit. B: ventral interior of specimen PMU In 457 from the mud mound (Volkhov Formation) at Volkhov River. 2. Ujukella fastigata (Rubel). A: dorsal exterior of specimen PMU In 7. B: oblique anterior view of dorsal interior of specimen PMU In 4. C: ventral exterior of specimen PMU In 10. D: ventral interior of specimen PMU In 2. All specimens from Frizy Unit at Lava River. 3. Neumania paucicostata Egerquist. A: ventral view of conjoined specimen, PMU In 109. B: ventral interior of specimen PMU In 108. C: dorsal interior of specimen PMU In 107. All specimens from Zheltiaki Unit at Putilovo Quarry. 4. Apomatella ingrica (Pahlen). A & B: ventral exterior and interior of specimen PMU In 458. C & D: dorsal exterior and interior of specimen PMU In 459. Both specimens from Frizy Unit at Putilovo Quarry. 5. Oslogonites Öpik. A & B: ventral interior and exterior of specimen PMU In 499 from Frizy Unit at Lava River. 6. Gonambonites Pander. A: dorsal interior of specimen PMU In 460, Puilovo Quarry, Zheltiaki Unit. B: dorsal interior of specimen PMU In 461, Putilovo Quarry, Volkhov Formation. 7. Antigonambonites planus (Pander). A: ventral interior of specimen PMU In 462 from the mud mound at the Volkhov River. B & C: exterior and interior of dorsal valve, specimen PMU In 463, Frizy Unit, Lava River. D & E: exterior and interior of dorsal valve, PMU In 465, Frizy Unit, Lynna River. 8. Antigonambonites cf. costatus Öpik. A: ventral exterior of young specimen, PMU In 464, Frizy Unit, Lava River. 9. Raunites strophomenoides(Öpik). Ventral exterior showing shell ornamentation, PMU In 466, Putilovo Quarry, loose sample in Volkhov Formation. 10. Paralenorthis orbicularis (Pander). A & B: external and internal of ventral valve, PMU In 105, C: dorsal interior of specimen PMU In 106. Both specimens from Frizy Unit, Putilovo Quarry. 11. Raunites wolchowiana (Öpik). A & B: exterior and interior of fragmentary dorsal valve, PMU In 467, Frizy Unit, Putilovo Quarry.

30 31 Plate 4 Scale bar 1 mm if nothing else is stated.

1. Leoniorthis robusta Egerquist. A & B: exterior and interior of ventral valve, PMU In 111. C & D: dorsal exterior and interior of holotype, PMU In 110. Both specimens from Putilovo mud mound, Dikari Unit. 2. Productorthis aculeata (Pander). A: exterior of ventral valve, PMU In 468, lowermost Frizy Unit, Putilovo Quarry. B: interior of ventral valve, PMU In 197, Dikari Unit, Putilovo mud mound. C: exterior of dorsal valve, PMU In 469, lowermost Frizy Unit, Putilovo Quarry. D: interior of dorsal valve, PMU In 199 Dikari Unit, Putilovo mud mound. 3. Glossorthis Öpik. A: ventral view of conjoined specimen, PMU In 470. B: internal of ventral valve, PMU In 471. C: external of dorsal valve, PMU In 472. D: internal of dorsal valve, PMU In 473. All specimens from Dikari Unit, Putilovo mud mound. 4. Ranorthis rotunda sp. nov. A: interior of dorsal valve, PMU In 179. B & C: ventral and dorsal exterior of conjoined specimen, PMU In 180. Both specimens from Dikari Unit, Putilovo mud mound. 5. Ranorthis norvegica Öpik. Interior of dorsal valve, PMU In 474, Zheltiaki Unit, Putilovo Quarry. 6. Ranorthis carinata Rubel. A: interior of dorsal valve, PMU In 476. B: interior of ventral valve, PMU In 475. Both specimens from Frizy Unit, Putilovo Quarry. 7. Skenidioides minutus sp. nov. A: interior of dorsal valve, holotype, PMU In 510. B: exterior of ventral valve, PMU In 515, both specimens from Putilovo Quarry, Zheltiaki Unit. 8. Nothorthis penetrabilis Rubel. A: dorsal exterior of a coarsely ribbed morphotype, PMU In 211, Dikari Unit, Putilovo mud mound. B & C: exterior and interior of dorsal valve, PMU In 103. D: ventral interior, PMU In 104. The two latter specimens from Zheltiaki Unit, Putilovo Quarry. 9. Paurorthis parva (Pander). A: dorsal interior of specimen with well developed mantle canals, PMU In 207. B: dorsal interior of specimen with pits on the internal surface of the shell, PMU In 477. Both specimens from Frizy Unit, Putilovo Quarry. C: exterior of dorsal valve with well developed pseudopunctae, PMU In 98, Frizy Unit, Lava River. D: internal of ventral valve with pitted inner surface, PMU In 478, Frizy Unit, Putilovo Quarry

32 33 Plate 5 Scale bar 2 mm

1. Porambonites trigonus Pander. A, C & E: ventral, anterior and front view of conjoined specimen, PMU In 452, Frizy Unit, Lynna Ri- ver. B & D: dorsal and posterior view of conjoined specimen, CNIGR 23/13101, loose sample in Volkhov Formation, Putilovo Quarry. 2. Porambonites reticulatus Pander. Dorsal fold with characteristic ornamentation, PMU In 451, Volkhov Formation, Putilovo Quarry. 3. Idiostrophia tenuicostata sp. nov. A & B: dorsal and ventral view of conjoined specimen, CNIGR 15/13101, loose sample in Volkhov Formation, Volkhov River.