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sessile colonial, filter-feeding animals, many of which possess hard carbonate skeletons of different morphology. The bryozoan faunas of the Ordovician of Estonia were studied early by famous naturalists such as Karl Eduard von Eichwald and Władisław Dybowski. Later, in the 20th century, many palaeontologists, among them Ray Bassler, Hendrik Bekker, and Ralf Männil, devoted extensive studies to the Ordovician bryozoans of Estonia. Soviet and Russian specialists contributed to the knowledge about this important group of fossils with numerous publications. The Ordovician deposits bearing abundant and well-preserved bryozoans are well exposed and often easily accessible. Therefore, the Estonian bryozoan faunas are much better studied than the contemporary assemblages of Sweden or Norway. Few representatives of this phylum appeared in the sediments of the Lower Ordovician, but then the group experienced a rapid diversification. The current evaluation of the data (published and based on the results of our own research) on the distribution of bryozoans in the Ordovician (Tremadoc–Hirnantian) deposits of Estonia revealed 194 species of 90 genera. The most diverse bryozoan group is trepostomes, with 77 species of 36 genera. The Sandbian and the Katian show the highest species richness of bryozoans, with 92 and 112 species, respectively. During the Hirnantian, bryozoans in Estonia experienced an immense diversity drop, with only a few species passing through the Silurian. This pattern mirrors the global development of bryozoan faunas during the Ordovician. Ordovician bryozoans of Estonia have been found in diverse environmental settings. The best-known deposit containing excellently preserved bryozoans is kukersite. This oil shale was formed in shallow subtidal shelf conditions, and contains more than 60 bryozoan species. Another famous bryozoan locality is the reefs of the Vasalemma Formation (Katian), exposed in the Vasalemma quarry. The bryozoans found in the Ordovician deposits of Estonia reveal a great variety of growth forms adapted to different biotopes of the sea bottom. The sizes of bryozoans vary immensely within the same assemblages. Some massive trepostomes such as Diplotrypa petropolitana attained heights of up to 20 cm, whereas species such as the cyclostome Kukersella borealis developed colonies less than 0.5 mm in diameter.

Bryozoans were common benthic invertebrates in the Silurian seas. The large biodiversity among Silurian benthic organisms prompted diversified interactions, and as a result bryozoans hosted many other organisms as symbionts. Here we analyse the cystoporate bryozoan Fistulipora przhidolensis and unidentified trepostomes intergrown with auloporid tabulate corals and putative hydrozoans. The material comes from the uppermost Přídolí Series (Late Silurian) of the Sõrve Peninsula, Saaremaa, Estonia. Our analysis shows that the interaction was beneficial for both organisms—cnidarians benefited from feeding currents created by the host bryozoan, while the latter benefited from the protection from predators by cnidae, it can thus be classified as mutualism. Such associations are common in modern seas. The analysed organisms are typically encrusting when the symbiosis is absent, when intergrown they display erect, branching morphologies, raised over the substratum, thus exploiting a higher suspension-feeding tier. While similar associations were known from the Devonian, we demonstrate that this novel ecological strategy for greater resource exploitation started as early as the latest Silurian.

The reefs of the Vasalemma Formation, late Sandbian, Late Ordovician, of northern Estonia contain an exceptionally rich and abundant bryozoan fauna. They are an example of contemporaneous bryozoan-rich reefs known from around the world, representing the peak diversification interval of this group during the Ordovician. The diversification is associated with global climatic cooling and increasing atmospheric and sea water oxygenation. However, the mechanisms that led to the bryozoan diversification are poorly known. Here we estimate the bryozoan richness (α and γ diversity) and turnover (β diversity) at the level of samples, reefs, and formations in the Vasalemma Formation. The resulting richness and turnover values differ among the three observational levels and hence are scale dependent. A pattern with lowest between-reef turnover and relatively high between-sample turnover could be detected, reflecting high small-scale (within reef) heterogeneities in lithology and original bryozoan habitat. This is consistent with the hypothesis that small-scale substrate heterogeneity was the most important diversification driver in the Vasalemma Formation.

Molecular evidence has long indicated that aquatic animals called bryozoans should be found among the fossils of the Cambrian period, around 541 million years ago. Yet they have been conspicuously absent, until now. The discovery of elusive fossils provides insight into animal evolution.

Some phyla seem to have missed this biodiversification event, as judged from their absence in the fossil record for the Cambrian period (which ran from 541 million to 485 million years ago). Mineralized body parts have a higher chance of fossilization than do unmineralized body parts, leading bryozoans to leave an impressive fossil record, especially for the Stenolaemata from the Palaeozoic era (541 million to 252 million years ago). Stenolaemata - the group of calcite-skeleton-containing bryozoans that is most abundant and diverse in the Palaeozoic - are assumed to have been derived from an unknown, soft-bodied ancestor described as being ctenostome-like, with an unmineralized body wall and a box-shaped zooecia (the compartment surrounding the animal's zooids).

Three species of trepostome bryozoans formed syn vivo associations with the Cornulites in the Late Ordovician of Estonia. Cornulites sp. and Mesotrypa excentrica presumably formed a true symbiotic association. This is the first known case of symbiosis between cornulitids and bryozoans. It is not known whether this symbiotic association was obligatory of facultative for the cornulitid, but it was facultative for the bryozoan. In this association cornulitids may have competed for the food with bryozoans and the association may have been parasitic. The remaining associations between cornulitids and bryozoans were accidental. Most common skeletonized endobionts of the Ordovician bryozoans were not cornulitids, but conulariids and rugosans.

Lower Devonian (Pragian-Emsian) reefal deposits of Sierra Morena (SW Spain) contain locally abundant calcified cyanobacteria, calcareous algae, and various microfossils including foraminifers. Calcified cyanobacteria are represented by Girvanella spp. A–C, which form crusts and clumps of various shapes. Supposed green algae (?Dasycladales) are represented by a new genus with one new species, Bediaella hispanica gen. et sp. nov. Algospongia include Vasicekia margaritula (Saltovskaya, 1986) n. comb. Microproblematica are represented by Rothpletzella sp. The studied assemblages indicate photic and warm conditions in a shallow and well-agitated environment with normal salinity, and probably mirror episodes of shallowing due to eustatic sea level fluctuations.

Bryozoans, stromatoporoid sponges, and tabulate corals, all colonial metazoans with lamellar, encrusting growth forms, developed and simultaneously diversified during the Great Ordovician Biodiversification Event (GOBE). After revisiting some classic Lower, Middle, and Upper Ordovician reef localities in Laurentia (Franklin Mountains, west Texas, Mingan Islands in eastern Canada, and Champlain Valley in northeastern United States) and Baltica (northern Estonia) and reviewing the literature, we demonstrate that during the Ordovician a newly emerging consortium of sheet-like bryozoans, stromatoporoid sponges, and tabulate corals locally bound together by microbes, automicrite, and cement and solidly rooted in sediment became the dominant reef-builders globally. The diversification of these sheet-like metazoans (SLM), however, clearly lagged behind the first appearance of their respective skeletal ancestors. Their habitat expansion can be exemplified as a case of simultaneous ecological fitting and ecosystem engineering when the independently evolved shared traits were simultaneously co-opted and became advantageous under globally different environmental conditions. This interaction led to the evolutionary diversification of colonial metazoans during the GOBE and to the expansion of novel reef habitats in previously soft-surface settings; a transformation that forever changed marine reefal ecosystems.

Eight bryozoan species are described from the Hanchiatien Formation (lower Silurian, Telychian) of southern Chongqing, South China. Four species are new: the trepostomes Asperopora sinensis n. sp., Trematopora jiebeiensis n. sp., and Trematopora tenuis n. sp., and the fenestrate Moorephylloporina parvula n. sp. One species, the cystoporate Hennigopora sp. indet., is described in open nomenclature. Moorephylloporina parvula n. sp. is eurytopic, occurring in all types of facies within the bioherms. Erect MoorephylloporinaBassler, 1952, TrematoporaHall, 1852, and LeioclemaUlrich, 1882 formed pioneering communities on weakly cemented substrata, whereas encrusting FistuliporaM‘Coy, 1849, HennigoporaBassler, 1952, and AsperoporaOwen, 1969 occurred on hardgrounds and formed densely compact framestones. Robust branched Trematopora and Leioclema tend to occur out of the reef core (framework) where they could have formed reef-flank thickets in more agitated conditions. The generic composition of the studied fauna correlates with other localities in South China, and they show general paleobiogeographic relations to Siberia and Indiana, USA.

Ten bryozoan species are described from the Andrecito and Tierra Blanca members of the Lake Valley Formation (Mississippian) of Sierra County, New Mexico, USA. One genus, with one species, is new—a cystoporate, Cystomeson sierraensis n. gen. n. sp. The bryozoans indicate quieter and deeper conditions in the Andrecito Member and more agitated and shallower conditions in the Tierra Blanca Member. The species identified in this study are endemic to North America, whereas at the generic level, the composition is rather cosmopolitan.