Palaeogeography, Palaeoclimatology, Palaeoecology 436 (2015) 58–63

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Palaeogeography, Palaeoclimatology, Palaeoecology

j ourna l homepage: www.e lsev ie r .com/ locate /pa laeo

Symbiotic interactions in the Ordovician of Baltica

Olev Vinn a,⁎, Mark A. Wilson b

a Institute of Ecology and Earth Sciences, University of Tartu, Ravila 14A, 50411 Tartu, Estoniab Department of Geology, The College of Wooster, Wooster, OH 44691, USA

⁎ Corresponding author.E-mail addresses: olev.vinn@ut.ee (O. Vinn), mwilson@

http://dx.doi.org/10.1016/j.palaeo.2015.06.0440031-0182/© 2015 Elsevier B.V. All rights reserved.

a b s t r a c t

a r t i c l e i n f o

Article history:Received 21 March 2015Received in revised form 6 June 2015Accepted 28 June 2015Available online 6 July 2015

Keywords:SymbiosisBioclaustrationsBiodiversificationBryozoansBalticaOrdovician

Eleven symbiotic associations between taxa occur in the Ordovician of Baltica, most involving colonial animals.Bryozoans formed the most numerous associations (including possible polychaete bioclaustrations, possiblepolychaete borings, conulariids, and crinoids) and had the highest number of symbiosis cases. In Baltica, theLate Ordovician symbiotic associations differ from those in the Middle Ordovician by a remarkable increase inthe numbers of recorded cases. This is most likely explained by the Great Ordovician Biodiversification Event(GOBE). The higher faunal diversity may have created more opportunities for symbiotic relationships. Thesechanges in the symbiotic interactions in the Ordovician of Baltica were probably not related to climate change,but had an evolutionary cause.

© 2015 Elsevier B.V. All rights reserved.

1. Introduction

The history of symbiotic interactions helps us better understand theecology of extinct organisms and the process of evolution in general.Symbiotic interactions formed an important part of the relationshipsbetween the organisms in the early Palaeozoic. Parasitic associationshave an especially long evolutionary history, with the earliest recordsfrom the early Cambrian (Baumiller and Gahn, 2002). Bioclaustrationsare one of the best ways to preserve symbiotic associations (Palmerand Wilson, 1988; Taylor, 1990; Tapanila, 2005; Zapalski, 2007;Zapalski and Hubert, 2010; Zapalski, 2011). A bioclaustration is createdwhen a symbiont, usually soft bodied, is embedded within a skeleton-ized host organism (Palmer and Wilson, 1988; Taylor, 1990). Othercases of symbiosis involve the attachment of a sclerobiont to anotherorganism where the skeletal structures show that both were alive atthe same time (Liddell and Brett, 1982).

The Ordovician of Baltica has a relatively good record of certain andpossible cases of symbiosis (Männil, 1959; Vinn andMõtus, 2012; Vinnet al., 2014a, b). In this study we focus only on confirmed cases of sym-biosis where the skeletal structures indicate that both organisms weregrowing together. Conulariids (Männil, 1959), cornulitids (Vinn andMõtus, 2012) and possible polychaetes (Männil, 1959; Vinn, 2004,2005; Vinn et al., 2014a,b) were common symbionts in bryozoans andtabulate corals of the Ordovician of Baltica.

All the Ordovician series in Baltica are well exposed in Scandinavia,Estonia and Russia. Drill cores from the other areas of Baltica have

wooster.edu (M.A. Wilson).

added more stratigraphic information. The faunas of the Tremadoc totheHirnantian of Baltica arewell studied (Raukas and Teedumäe, 1997).

The aim of this paper is: 1) to summarize the symbiotic associationsfound in the Ordovician of Baltica; 2) to find trends in the distribution ofsymbiosis in this region; and 3) to find possible controls on the symbi-otic interactions in the Ordovician of Baltica.

2. Symbiotic associations

Twenty-four cases of certain symbiosis, half of which are withbryozoans, have been reported from the Ordovician of Baltica (Fig. 1,Table 1). Colonial animals are most abundant in the symbiotic associa-tions of the Ordovician of Baltica. Most (70%) of the recorded symbioticassociations involve at least one colonial partner. Associationswith bryo-zoans were most common (40% of associations). Bryozoans hosted themost diverse fauna of endobiotic symbionts; these symbionts were allnon-colonial (Anoigmaichnus, Sanctum, ‘Hicetes’, and Conularia; Männil,1959; Wyse Jackson and Key, 2007; Vinn et al., 2014b). Some bryozoanswere epibionts themselves on living crinoid stems. Crinoids hostedparasites that created Tremichnus traces. The next most numerous casesof symbiosis were associations with tabulate corals and brachiopods.Among tabulates, associations with cornulitids and possible polychaetes(i.e. Chaetosalpinx) are known (Vinn andMõtus, 2012). Only three symbi-otic associations between non-colonial animals, hosted by brachiopods(i.e. brachiopod–‘polychaete’ bioclaustration and brachiopod–Trypanitesassociations) and chitinozoans (i.e. chitinozoan–‘spore’ associations),have been reported from the Ordovician of Baltica (Grahn, 1981; Vinn,2004, 2005; Vinn et al., 2014a).

Fig. 1. Number of symbiosis cases in the Ordovician of Baltica.

Table 1Distribution of symbiotic associations in the Ordovician of Baltica.

Taxon A Taxon B

Crinoid Ceramoporella granulosaProtoheliolites dubius Cornulites aff. celatusProtoheliolites dubius Conchicolites hosholmensisProtoheliolites dubius Chaetosalpinx sp.Propora speciosa Cornulites aff. celatusStelliporella parvistella Cornulites aff. celatusHallopora dybowski Conularia sp.Monotrypa jewensis Conularia sp.Prasopora insularis esthonica ‘Hicetes’ tracesMesotrypa excentrica ‘Hicetes’ tracesDiplotrypa abnormis Conularia sp.Esthoniopora communis Conularia sp.Monotrypa jewensis Conularia sp.Crinoid Atactoporella balticaCrinoid Crepipora schmidtiGlossorthis sp. Trypanites (‘blister’)Clitambonites squamatus Burrinjuckia clitambonitofiliaTrepostome bryozoan Sanctum sp.Dendrograptus rigidus TubothecaAcanthograptus sp. 1 TubothecaMesotrypa bystrowi Anoigmaichnus odinsholmensisRhabdochitina gracilis Spore-like bodiesDesmochitina amphorea Spore-like bodiesRhipidocystis concentricus TremichnusRhipidocystis baltica TremichnusAntigonambonites Trypanites (‘blister’)

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2.1. Bryozoan–‘polychaete’ bioclaustration association

In this association, soft-bodied ‘worms’ (i.e. Anoigmaichnus and‘Hicetes’ trace producers) were embedded within a host bryozoancolony, leaving only their apertures free on the growth surface of thebryozoan (Männil, 1959; Vinn et al., 2014a,b) (Fig. 2). This associationoccurs only in bryozoans with massive skeletons. There can be several‘worms’ per single host colony. The ‘worms’may have gained protectionagainst predators by being embedded inside the bryozoan skeleton(Vinn et al., 2014a,b). This association may have been parasitic basedon analogies with similar bioclaustrations in Devonian cystoporatebryozoans (Ernst et al., 2014) and in tabulates (Zapalski, 2007, 2011).Theworms initially bored into a living bryozoan and killed a few zooids,which had negative effect on host bryozoan colony.

2.2. Bryozoan–‘polychaete’ boring association

Soft-bodied ‘worms’ (as inferred in the trace fossil Sanctum) some-times bored into living bryozoan colonies, which is indicated by skeletaltissue repair (Wyse Jackson and Key, 2007). The ‘worms’ may haveacquired protection from predators by this embedment in a massiveskeleton (Vinn et al., 2014b). The ‘worms’may have had negative effecton the bryozoan colony by competing with it for nutrients (WyseJackson and Key, 2007; see also Ernst et al., 2014).

2.3. Bryozoan–Conularia association

In this association, conulariids (Conularia sp.) are embedded in bryo-zoan hosts, leaving only their apertures free on the growth surface(Fig. 3). There are one to four conulariids per host (Männil, 1959).Conulariids possibly had protection from predators and a relatively sta-ble growth substrate by their embedmentwithin the bryozoan skeleton.Conulariids were sedentary upright growing organisms and theirtissues near the aperture must have been capable of preventing over-growth. Some bryozoans in these associations were probably growingon algal fronds or stems of unknown organisms (Männil, 1959). Inthis latter case the conulariids also benefitted from a higher tier forfilter-feeding. The symbiont's influence on the host bryozoan is unclear;

Age (locality) References

Katian (Estonia) Männil (1959)Katian (Estonia) Vinn and Mõtus (2012)Katian (Estonia) Vinn and Mõtus (2012)Katian (Estonia) Vinn and Mõtus (2012)Katian (Estonia) Vinn and Mõtus (2012)Katian (Estonia) Vinn and Mõtus (2012)Katian (Estonia) Männil (1959)Katian (Estonia) Männil (1959)Sandbian (Estonia) Männil (1959)Sandbian (Estonia) Männil (1959)Sandbian (Estonia) Männil (1959)Sandbian (Estonia) Männil (1959)Sandbian (Estonia) Männil (1959)Sandbian (Estonia) Männil (1959)Sandbian (Estonia) Männil (1959)Sandbian (Estonia) Vinn (2005)Sandbian (Estonia) Vinn et al. (2014a)Sandbian (Estonia) Wyse Jackson and Key (2007)Darriwilian (Öland) Skevington (1963)Darriwilian? (Poland) Kozłowski (1970)Darriwilian (Estonia) Vinn et al. (2014b)Darriwilian (Öland) Grahn (1981)Darriwilian (Öland) Grahn (1981)Darriwilian (NW Russia) Rozhnov (1989)Dapingian (NW Russia) Rozhnov (1989)Dapingian (Estonia) Vinn (2004)

Fig. 2.Bryozoan–‘polychaete’ bioclaustration association.Anoigmaichnus odinsholmensis inMesotrypa bystrowi from Darriwilian of Osmussaar Island, Estonia (GIT 697-507).

60 O. Vinn, M.A. Wilson / Palaeogeography, Palaeoclimatology, Palaeoecology 436 (2015) 58–63

a small number of embedded conulariids probably did not have a stronginfluence on the bryozoan. No other cases of this type of interactionwith conulariids are known.

2.4. Crinoid–bryozoan association

Bryozoan colonies were sometimes attached to the stems of livingcrinoids (Männil, 1959). The bryozoans probably benefitted from ahigher tier for feeding. The encrusting bryozoan colonies may haveinfluenced the flexibility of the host stems.

Fig. 3. Bryozoan–Conularia association from Sandbian of Estonia, modified after Männil(1959).

2.5. Eocrinoid–Tremichnus association

Rozhnov (1989) described small almost cylindrical pits on the sur-face of theca in Rhipidocystis baltica and Rhipidocystis concentricusunder the name Balticapunctum inchoatus. These traces are identicalto Tremichnus (Brett, 1978, 1985) and the latter name is used here.Tremichnus traces were probably made by echinoderm parasites.

2.6. Heliolitid–Cornulites association

Cornulites are often embedded in the coralla of heliolitids (Fig. 4),leaving only their apertures free on the growth surface. There can beseveral Cornulites per host. Cornulites may have had additional protec-tion against predators by being embeddedwithin theheliolitid skeleton.The symbionts' influence on the host heliolitid is unknown, but it waslikely parasitic as numerous embedded Cornulites would have reducedthe feeding efficiency of the host coral (Vinn and Mõtus, 2012).

2.7. Heliolitid–‘polychaete’ bioclaustration association

In this association, rare soft-bodied ‘worms’ (i.e. as with the tracefossil Chaetosalpinx) are embedded within a host heliolitid coral, withonly their apertures free on the growth surface. The organisms thatformed Chaetosalpinxmay have had protection from predators throughthis embedment inside the coral skeleton (Vinn and Mõtus, 2012).According to Zapalski (2007, 2011), this association may have beenparasitic.

2.8. Brachiopod–‘polychaete’ bioclaustration association

Occasionally a soft-bodied worm-like parasite caused an outgrowth(i.e. bioclaustration) of secondary shell in the mantle cavity of brachio-pods (Vinn et al., 2014a) (Fig. 5).

2.9. Brachiopod–Trypanites association

In this case soft-bodied ‘worms’ bored into the shells of livingbrachiopods, forming the trace fossil Trypanites. The syn vivo nature ofthis association is indicated by brachiopod internal shell repair (Vinn,2004, 2005). Numerous Trypanites-forming ‘worms’ could have had anegative effect on the host brachiopod by depleting its resources andpossibly competing for nutrients. The ‘worms’ benefitted from a stablesubstrate and protection from predators (Vinn, 2004, 2005).

Fig. 4. Heliolitid–cornulitid association. Cornulites aff. celatus in Protoheliolites dubius fromlate Katian of Estonia (GIT 520-140).

Fig. 5.Brachiopod–‘polychaete’ bioclaustration association.Burrinjuckia clitambonitofilia inClitambonites squamatus from the Sandbian of NE Estonia (GIT 343-236).

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2.10. Graptoloid–tubotheca association

In this association a soft-bodiedworm-like parasite caused formationof tubotheca in the rhabdosomes of graptoloids (Kozłowski, 1970). Mostlikely, they belong to the polychaete class Eunicea. Tubothecae funda-mentally differ from normal graptolite thecae by their continuous sizeincrease, irregular morphology, and lack of a fusellar microstructure(Kozłowski, 1970).

2.11. Chitinozoan–‘spore’ association

Grahn (1981) described parasitic ‘spore’-like organisms that were at-tached to the surface of a chitinozoan, sometimes in large numbers. These‘spores’ have been interpreted as cysts of ectoparasitic nanoorganismsthat resemble ciliates and amoebae. These ‘spores’ are not mineralizedand are preserved as organic matter (Grahn, 1981).

3. Stratigraphic distribution of symbiotic associations and symbiosiscases

The longest ranges of these symbiotic associations in the Ordovicianof Baltica are the brachiopod–Trypanites (Dapingian to Sandbian),eocrinoid–Tremichnus (Dapingian to Darriwilian) and bryozoan–‘polychaete’ bioclaustration (Darriwilian to Sandbian) relationships(Table 1). The other associations have been reported from only singleseries. TheMiddleOrdovician and LateOrdovician symbiotic associationsof the Baltica differ significantly. In the Middle Ordovician there areonly four associations: graptoloid–tubotheca, eocrinoid–Tremichnus,chitinozoan–‘spore’, and bryozoan–polychaete. The Late Ordovicianassociations are dominated by bryozoans. There is a remarkable increasein the number of symbiotic associations, going from four in the MiddleOrdovician to eight in the Late Ordovician.

3.1. Generic and group diversity of symbiotic interactions

The group diversity increased in the Middle Ordovician and wasrelatively stable from the Darriwilian to the Katian (Table 1). There aretwo symbiotic associations in the Dapingian, four in the Darriwilian,six in the Sandbian, and four in the Katian. There are at least four generaforming symbiotic associations in the Dapingian, at least ten genera inthe Darriwilian, at least sixteen genera in the Sandbian, and nine inthe Katian.

3.2. Number of symbiosis cases (interactions between different species)

There is a significant increase in the number of symbiosis cases(from eight to 18) in the Late Ordovician of Baltica. There is two in theDapingian, six in the Darriwilian, ten in the Sandbian, and eight in theKatian (Fig. 1, Table 1).

4. Discussion

4.1. Symbiotic associations

The colonial animals of the Ordovician of Baltica may have beendominant among the symbiotic organisms because of their possiblygreater host tolerance (i.e. they may have been easier to infest), andsmaller symbionts may have likely preferred massive skeletons, suchas those of some bryozoans.

Symbiotic associations involving bryozoans are the most prominentin the Ordovician of Baltica. Similarly, symbiosis cases involving bryo-zoans are most numerous in the Ordovician of Baltica. This may bedue to the relatively high diversity of bryozoans and the abundance oflarge colonies (Männil, 1959) capable of hosting various endobionts.The dominance of bryozoans is different from that of the Silurian ofBaltica where the symbiotic associations with stromatoporoids aremost common (Vinn, pers. obs.). Stromatoporoids occur also in theLate Ordovician of Baltica (Nestor, 1964), but it is possible that the sym-biont tolerant forms only appeared later in the Silurian. However, thenumber of total symbiotic associations in the Ordovician (eleven) andSilurian (thirteen) is similar in general (Vinn, pers. obs.).

It is interesting to note that there are some differences between thesymbiotic associations of Laurentia and Baltica. Most notable is the lackof the platyceratid–crinoid association (Morris and Felton, 1993) in theLate Ordovician of Baltica. Both platyceratids and crinoids occur in theLate Ordovician of Baltica, so it is possible that this association is stillto be discovered.

4.2. Biofacies

One could ask how comparable are the biofacies in this study: cansome of the differences in the dynamics of symbiotic interactions bean artifact of comparing different community types rather than age?In general, most of samples of this study are derived from similarshallow water carbonate accumulation paleoenvironments. However,the pre-Dapingian part of Ordovician is mostly represented by terrige-nous sediments in Baltica (Raukas and Teedumäe, 1997), and thecorresponding facies contained different communities that may havebeen less prone to symbiosis. Another problem is the lowering of bioticinteraction frequency in the Katian. Biodiversity overall is high duringthis time and it would be surprising if there were a genuine drop in or-ganism–organism interactions. Studied Katian fossils aremostly derivedfrom pure carbonates that contrast with the argillaceous carbonates ofthe Sandbian. It is possible that the facies available for sampling mayhave influenced the record of symbiosis in the Late Ordovician of Baltica,and that the lowering of biotic interaction frequency in the Katian is asampling artifact.

4.3. Evolutionary trends and the Great Ordovician Biodiversification Event(GOBE)

The remarkable increase of symbiosis cases in the Late Ordovicianof Baltica (eight cases in the Middle Ordovician versus 18 in the LateOrdovician) (Fig. 1, Table 1) is most likely explained by the GreatOrdovician Biodiversification Event (GOBE; Servais et al., 2009) alongwith the continuing increase in functional differentiation among marinefaunas (Knope et al., 2015). The higher diversity of faunas created moreopportunities for symbiotic relationships. The lack of recorded symbioticinteractions in the EarlyOrdovician of Baltica is likely not a sampling bias,

62 O. Vinn, M.A. Wilson / Palaeogeography, Palaeoclimatology, Palaeoecology 436 (2015) 58–63

and the appearance of symbiotic interactions in theMiddle Ordovician isalso possibly a function of theGOBE. Thus, the dynamics of the number ofsymbiosis cases in large temporal scale intervals (Early, Middle and LateOrdovician) is likely due to evolutionary innovations.

The Darriwilian (6 cases) to Sandbian (10 cases) increase in symbi-osis cases may especially be related to the diversification of bryozoansand appearance of taxa amenable for symbiosis. In the case of mutualis-tic relationships, the taxa amenable for symbiosis may have had evolu-tionary advantages over the taxa less amenable for symbiosis.

It seems that the diversity of potentially symbiotic groups increasedbefore (i.e. in the Darriwilian) the increase of symbiosis cases in theSandbian. The increase of generic diversity was also higher in theDarriwilian than in the Sandbian. Whether this is a general rule in theevolution of Ordovician symbiotic associations cannot be answeredwith our data.

All the following first appearances refer specifically to the knownrecord of Baltica. The bryozoans first appeared in the Floian of Baltica(Koromyslova, 2011). Their earliest symbionts are known from theDarriwilian of Estonia. Thus, the symbiotic relationships appearedrelatively shortly after the appearance of bryozoans in Baltica. Similarly,corals appeared in the early Katian, which is quite late compared toLaurentia (Darriwilian), and their first symbiotic endobionts are knownfrom late Katian (Vinn and Mõtus, 2012). However, stromatoporoidsappeared in the early Katian (Nestor, 1964), but their first symbiontsoccurred in the Early Silurian (Rhuddanian; Vinn et al., 2013). Thus, theearly appearance of symbionts in large skeletons of colonial animals isnot the general rule in the Ordovician of Baltica. Similarly, some solitaryorganisms had their first symbionts relatively early after their firstappearance, whereas others had a late appearance of symbionts.Chitinozoans that are known from the Tremadocian had their earliestsymbionts in the Darriwilian (Raukas and Teedumäe, 1997), whilebrachiopods that are known from the early Cambrian (Raukas andTeedumäe, 1997) had their earliest symbionts in the Dapingian.

The difference between the Middle and Late Ordovician symbioticassociations of Baltica could be explained by the diversification ofbryozoans and appearance of symbiont tolerant taxa. The relativelylate evolutionary appearance of new symbionts such as cornulitids inthe latest Darriwilian (Vinn, 2010) and non-boring symbiotic poly-chaetes (i.e. Chaetosalpinx) in the Katian (Tapanila, 2005) contributedto the difference.

4.4. Climatic change

During theOrdovician, Balticamoved froma temperate climate zoneto the tropics (Torsvik et al., 1992; Cocks and Torsvik, 2005). Symbiosisis very common among recent tropical animals, and species diversity isgenerally higher in tropical than in temperate seas (Barnes and Hughes,1999), creating more opportunities for symbiosis. It is possible that theabrupt increase in biodiversity and numbers of interactions in theDarriwilian to Sandbian may have partially been induced by warmingof the climate. However, the difference between Middle and LateOrdovician associations can best be explained by evolutionary causes.

4.5. End-Ordovician mass extinction event

It is possible that losses in biodiversity due to the O/S mass extinc-tion had an impact on organism to organism interactions across theHirnantian into the Silurian. Unfortunately, there is no data on thesymbiotic interactions from the Hirnantian of Baltica, which may wellbe an artifact of sampling. One could ask how the diversity and frequen-cy of organism interactions in the early Silurian compare with that inthe Ordovician. The number of symbiosis cases is six in the Llandoveryof Baltica (Vinn and Wilson, in press), which is slightly less than in theKatian (N = 8). Thus, the influence of O/S mass extinction was likelynot strong on the number of symbiosis cases, or it was confined to theHirnantian and Rhuddanian. The number of symbiotic associations in

theKatian and Llandoverywas the same (N=4). However, the symbioticassociations in the Katian and Llandovery are different; only theheliolitid–polychaete association is common. Thus, biotic changescaused by the O/S mass extinction influenced the taxonomic composi-tion of symbiotic associations.

Acknowledgments

Financial support to O.V. was provided by a Palaeontological Associ-ation Research Grant and Estonian Research Council projects ETF9064and IUT20-34. MW was supported by a Luce Grant from The CollegeofWooster. This paper is a contribution to IGCP 591 “TheEarly toMiddlePalaeozoic Revolution”. We are grateful to C. Brett and an anonymousreviewer for the constructive reviews.

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