Silurian Of Estonia Research Articles

Tentaculitids from the Silurian of Estonia

Tentaculitids from the Silurian of Estonia

New encrusting tentaculitoids from the Silurian of Estonia and taxonomic status of Anticalyptraea Quenstedt, 1867

ABSTRACT A new genus and species of encrusting tentaculitoid, Lindstroemiella eichwaldi, from the Silurian (Ludfordian Stage, Ludlow) of Saaremaa Island in Estonia, is described. This tentaculitoid shares common structural features (inwardly directed pseudopunctae and vesicles) with Anticalyptraea, but differs from the latter in having a spirally coiled, microconchid-like shell with a variously oriented aperture, thin and sharp transverse ridges and lacking an inverted cone-like morphology. Unlike other tentaculitoids (microconchids, trypanoporids, cornulitids), these encrusters, unique with respect to morphology and shell structure, have so far not been taxonomically classified at the ordinal level. Now, taking into account that such tentaculitoids are taxonomically and morphologically more diverse than previously assumed, we propose to include them in a separate order Anticalyptraeida. Unlike microconchids and cornulitids, anticalyptraeids are the least studied group of tentaculitoids and thus poorly recognized. In part, this may be due to their misidentification with associated spirally coiled microconchids, to which anticalyptraeids are very similar at juvenile stages. http://www.zoobank.org/lsid:zoobank.org:act:C1E9D9A4-555E-4F5A-BEDC-8046CCA58BD9

Endolymphatic structures in headshields of the osteostracan genus Tremataspis (Agnatha) from the Silurian of Estonia

Endolymphatic structures in headshields of the osteostracan genus Tremataspis (Agnatha) from the Silurian of Estonia

New cornulitid from the Ohesaare Formation (late Přidoli) of Saaremaa, Estonia

A new cornulitid species Cornulites baranovi sp. nov. is described from the Ohesaare Formation (late Přidoli) of Saaremaa, Estonia. The new species exhibits straight to slightly curved tubes that expand moderately in diameter, a vesicular tube structure and strong annular crests and costae. In addition to C. baranovi sp. nov., Conchicolites sp. also occurs in the Ohesaare Formation. The diversity of cornulitids is low in the Přidoli of Estonia, but not lower than in the Silurian of Estonia in general. C. baranovi often forms a symbiotic association with the bryozoan Fistulipora. It is not sure whether sealing off one cornulitid specimen by host bryozoan was a result of space competition or a post- mortem overgrowth. Specimens of C. baranovi also occur as solitary encrusters and aggregative encrusters in the Ohesaare Formation. C. baranovi presumably represents ecological generalists among the Silurian tentaculitoid tubeworms.

Ordovician and Silurian ichnofossils from carbonate facies in Estonia: A collection-based review

Trace fossils are common in the Ordovician and Silurian shallow marine carbonate succession of Estonia, with 45 ichnofossil genera and five bioclaustration structures identified, representing 31 categories of architectural designs and nine categories of ethological classification. Diverse soft sediment traces, bioerosional traces and bioclaustrations occur both in the Ordovician and Silurian. Diversity of trace fossils is similarly high in the Late Ordovician and Silurian, but markedly lower in the Middle Ordovician. This could be explained by the fact that during the Late Ordovician, Baltica drifted to the subtropical climatic zone where ichnofauna is usually more diverse than in temperate climatic settings. In addition, the Great Ordovician Biodiversification reached its peak in the Late Ordovician for many groups of organisms, which further contributed to the increase in ichnodiversity. Distribution of trace fossils is also controlled by the type of sedimentation, so that the mixed carbonate-siliciclastic systems prevailing in the Late Ordovician and Silurian have higher ichnodiversity than the pure carbonate settings of Middle Ordovician age. Feeding and locomotion traces are relatively rare in the Ordovician and Silurian of Estonia with the exception of the feeding structure Arachnostega, which is formed inside of protective shells and therefore has abundant occurrences. Bioerosional trace fossils may be extremely common in places, with a large number of different genera in the Upper Ordovician, supporting the idea of the Ordovician Bioerosion Revolution.

Rare arthropod traces from the Ordovician and Silurian of Estonia (Baltica)

Rare arthropod traces from the Ordovician and Silurian of Estonia (Baltica)

The oldest ascocerid cephalopod from the Silurian of Estonia and notes on the biogeography of the order Ascocerida (class Cephalopoda)

The oldest ascocerid cephalopod from the Silurian of Estonia and notes on the biogeography of the order Ascocerida (class Cephalopoda)

Bioerosion of inorganic hard substrates in the Silurian of Estonia (Baltica)

Carbonate hardgrounds are unevenly distributed in the Silurian of Estonia, with only three bioeroded hardgrounds in the Telychian and one in the late Pridoli. There seem to be no trends in the bioerosion intensities and ichnotaxonomical diversity in the Silurian of Estonia. Only Trypanites occurs in the hardgrounds of the Silurian of Estonia and ichnological diversity of bioeroded organic hard substrates, containing Trypanites, Palaeosabella and Osprioneides is higher than inorganic substrates. The small number of bioeroded inorganic substrates could indicate that these substrates were probably less important than the organic hard substrates for the development of seafloor ecological niches in the Silurian of Estonia. The average bioerosion intensities of the hardgrounds are relatively high, but not unusual for the Silurian.

Tremichnus in crinoid pluricolumnals from the Silurian of western Estonia (Baltica)

Rare pits attributed to Tremichnus have been found in crinoids from the Silurian of Estonia. The Rhuddanian Tremichnus is the earliest symbiont in crinoid columnals of Baltica. These pits presumably were domiciles of unknown organisms. Tremichnus had a negative effect on the host crinoid as demonstrated by swollen columnals. Tremichnus in the Silurian of Estonia is less common than similar traces in the Silurian of nearby Gotland. The most important aspect of this study is the rarity of this interaction in these samples in contrast to most other samples of comparable age elsewhere. These structures have a very patchy distribution.

The trace fossil Zoophycos from the Silurian of Estonia

The trace fossil Zoophycos from the Silurian of Estonia

Biodiversity of the Silurian osteostracans of the East Baltic

ABSTRACTThe sculpture and histology of osteostracan head shields and trunk squamations from the Silurian of Estonia are described, illustrated and used for the identification of disarticulated microremains collected from outcrop sections and numerous drill cores in Estonia and Latvia over the last 40 years. The scattered osteostracan material contains thousands of specimens of scales and shield fragments. The sculpture and histology of species of the previously identified eight genera in the region (Tremataspis,Dartmuthia,Saaremaaspis,Oeselaspis,Aestiaspis,Thyestes,Procephalaspis, Witaaspis) are redescribed, together withAteleaspis, found in Estonia for the first time. The sculpture on the cornua of several taxa is described for the first time. The new taxaTremataspis perforatasp. nov.,Dartmuthia procerasp. nov.,Eldaaspis mikliigen. et sp. nov.,Tahulaspis ordinatagen. et sp. nov.,Tahulaspis praeviagen. et sp. nov.,Meelaidaspis gennadiigen. et sp. nov. andOhesaareaspis ponticulatagen. et sp. nov. are established, based upon sculpture and histological characteristics of the exoskeleton. The supraoral field with denticles of that field are described for the first time inOeselaspis pustulata, as is the supraoral plate with buccal denticles inMeelaidaspis gennadiigen. et sp. nov. Thin sections of all taxa (except ofWitaaspis) have been studied. This work sheds light on East Baltic osteostracan biodiversity from the Maasi Beds of the Jaagarahu Stage, Sheinwoodian, lower Wenlock up to the Ohesaare Stage, upper Přidoli, Silurian.

Mikrofossilien aus dem Silur Estlands und der insel Ösel

Eisenack, A.: Mikrofossilien aus dem Silur Estlands und der Insel Osel. [Microfossils from the Silurian of Esthonia and the Isle of Osel.] Geologiska Foreningens i Stockholm Forhandlingar, Vol. 92, pp. 302–322. Stockholm, September 30, 1970. The present report deals with microfossils mostly of organic matter from the Silurian of Estonia and the Isle of Osel. There are several groups met with: Chitinozoa, the most frequent ones, Foraminifera, Melanoskleritoidea, Annelida, Hystrichophyta and Algae. Other groups are only briefly mentioned. The annelids have yielded some new forms of mandibles and carriers; the maxillae are not dealt with here. In stratigraphical view there is a good correspondence with the equivalent strata of Gotland and for the higher zones of Osel with the Beyrichian limestone, a well known and fossiliferous kind of glacial boulders of Downtonian age. Dieser Bericht behandelt Mikrofossilien aus dem Silur Estlands und der Insel Osel, und zwar hauptsachlich solche aus organischer Substanz: ...