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The mid–late Homerian Age of the Silurian Period was a time of intense changes in biota, oceanic chemistry, and sea level and is known as the lundgreni extinction (for the graptolite extinctions), the Mulde bioevent (for the conodont turnover event) or the Homerian carbon isotope excursion (CIE) probably related to glacially influenced climate perturbation. New information on this interval from the deep water sedimentary and graptolite succession of the Kielce Region (Holy Cross Mountains, Poland) of the northern margin of the Małopolska Block is presented here based on analysis of the Prągowiec Ravine section. The lundgreni–nilssoni graptolite biozones interval have been recognized there. This interval is composed by dark shales with very rare benthic fauna, which indicate the deep open-marine (pelagic) paleoenvironment. Ten samples were taken for the δ13Corg analysis from the lundgreni (2 samples), parvus (2 samples), praedeubeli (2 samples), praedeubeli–deubeli (1 sample), ludensis (2 samples) and nilssoni (1 sample) biozones. According to the δ13Corg results, the first positive δ13Corg excursion of the Mulde Bioevent is well recognized. The δ13Corg values rise from −30.7 – −30.1 ‰ in the lundgreni Biozone to −29.3 – −28.7 ‰ in the parvus Biozone and fall below −30 ‰ in the praedeubeli–deubeli interval. The second positive δ13Corg peak of the Mulde Event was not recognized in the Prągowiec Ravine. Based on the numerical comparisons using Raup-Crick metric of co-occurrences of graptolite species, the upper Homerian was characterized by significant between-biozone turnover of these taxa at the given locality.

Permian fishes and their isolated microremains are known from many localities in the Zechstein Basin. However, up to date the vertebrates have never been revealed in the southeasternmost part of this ancient sea. The new material consists of euselachian-type dermal denticles,? Listracanthus sp. dermal denticle,? Omanoselache sp. tooth, actinopterygian scales and actinopterygian teeth. Here, the detailed study of euselachian and actinopterygian remains, their stratigraphic distribution and geographical contexts is presented. Based on the qualitative analysis of teeth shapes several ecomorphotypes were described as well as the probable dietary preferences of fishes were reconstructed. These finds confirmed existence of small predators who fed on soft bodied prey as well as durophagous forms which were feeding on small shelly crustaceans or molluscs. The analysis of stratigraphic distribution of microremains, and their comparison with neighbouring sections revealed a spatially correlatable trend in increasing abundance of fishes in the more clayey parts of sections, interpreted to be positively associated with a sea level transgression event. [ABSTRACT FROM AUTHOR]

Two new forms of Pristiograptus dubius, here designated as varieties "A" and "B", are described and figured. Both were found in core samples representing the perneri through lundgreni biozones of the Wenlock epoch. The cores are from boreholes Šiupyliai-69, Parovėja-9, Likėnai-396, Paežeriai-222 and Sutkai-87 in central and northern Lithuania. The associated graptolites Cyrtograptus perneri Bouček, C. radians Törnquist, C. lundgreni Tullberg, Monograptus flemingii flemingii (Salter), M. testis testis (Barrande), Monoclimacis flumendosae (Gortani) and Pristiograptus pseudodubius (Bouček) (= P. parvus) are all indicative of the perneri, radians and lundgreni biozones of the Wenlock. Two species of Pristiograptus occur in this time-stratigraphic interval: P. dubius and P. lodenicensis. In P. dubius the degree and manner of extension of the thecal apertural lip (thecal hood) onto the succeeding theca distinguish it from otherwise very similar taxa. The thecal morphology of P. lodenicensis differs from that of a typical Pristiograptus in that the apertural lip has a central depression and is rounded into small lobes laterally.

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The monograptids from the Wenlock and Ludlow (mid- to late Silurian) of the palaeotropical Baltic Basin exhibit thickened ring structures (sicular annuli) over their initial phase of growth. Appearing before the lundgreni extinction event, they persisted throughout the remainder of the Silurian, fluctuating in number over that period. To better understand the mechanisms controlling their development and variation, counts of sicular annuli were taken from three well cores in Lithuania, compared between species in each sample and compared with contemporaneous gamma ray data, accompanied by the stable isotope (δ13C), and acritarch diversity data. Mean counts of annuli fluctuated greatly over the studied interval, but showed negligible variation between species, indicating that the trait is ecophenotypic. The fluctuation in annulus presence aligned with variations in fourth- and fifth-order cycles derived from the gamma ray trends, which represent significant sea level fluctuations, δ13C ratios, and primary productivity, suggesting that annuli were more plentiful in high-stand states which are associated with the wetter climate and more productive conditions, whereas dryer, less productive conditions were not conducive to annulus development. In light of this evidence, we hypothesise that the action of upwelling as a result of intensified storm events during wetter periods would have encouraged phytoplankton blooms, increasing construction of annuli. These results show the potential utility of sicular annuli in the study of Silurian climate change and give new insights into graptolite palaeoecology. [ABSTRACT FROM AUTHOR]

The late Permian time was a transformative period before the most severe mass extinction known. Even though fishes constitute a key component of marine ecosystems since the Silurian, their biogeographic patterns during the late Permian are currently insufficiently known. The new ichthyofaunal material described here comes from the southeastern part of the Zechstein Basin, from the calcareous storm sediments alternating with marls, which were deposited in less energetic conditions. Chondrichthyans and osteichthyans are reported here for the first time from the Nowy Kościół quarry in the SW Poland. The assemblage consists of various euselachian dermal denticles, actinopterygian scales and teeth, and isolated hybodontoid tooth putatively assigned as extremely rare ?Gansuselache sp. from the Permian. The diverse actinopterygian tooth shapes show significant ecological differentiation of fishes exploring sclerophagous, durophagous, and herbivory modes of feeding in the given part of the Zechstein Basin suggesting the presence of complex ecosystems even in hyper-saline conditions of an epicontinental sea. [ABSTRACT FROM AUTHOR]

Copyright of Estonian Journal of Earth Sciences is the property of Teaduste Akadeemia Kirjastus and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Iterative evolution has proved a difficult evolutionary phenomenon to study and interpret. Inferences of causality vary from study to study and quantitatively based phylogenetic reconstruction has never been attempted. In an effort to better understand iterative evolution we employed stratocladistics, gap analysis and disparity analysis to study the case of the Monograptidae in the aftermath of the late Silurian Cyrtograptus lundgreni extinction event. Our combination of gap analytical and stratocladistic techniques allowed us to elucidate the evolutionary relationships between the studied taxa. Based on our stratocladistic results we recommend the generic reassignment of five monograptid taxa. The stratocladistic results, in conjunction with morphological disparity analysis suggest the presence of a persistent developmental potential for the emergence of iteratively evolving characters. This persistent potential appears to be limited by extrinsic ecological constraints, which would have relaxed in the aftermath of the C. lundgreni extinction event. Our findings indicate that iterative evolution in the late Silurian Monograptidae is a product of the interaction of both intrinsic and extrinsic constraints on the acquisition of the iteratively evolving character, with the exact causality being dependent on the particular character. [ABSTRACT FROM AUTHOR]

Pristiograptus dubius pseudodubius and Pristiograptus lodenicensis were collected from outcrops of black pelagic shales of the Zdanów section of the Bardo Mountains (Sudetes, Poland). The species are easily distinguished from one another in that P. lodenicensis has distinct lobate processes on its thecae, whereas those of P. d. pseudodubius are comparatively unornamented. Our findings indicate that the age of the Lower Graptolitic Shales in the Zdanów is the middle part of the C. lundgreni graptolite Biozone (lower Homerian, upper Wenlock). The presence of P. d. pseudodubius at this site adds another locality to its global range, while the presence and abundance of P. lodenicensis further indicates the restriction of the latter species to the Rheic palaeo-ocean. [ABSTRACT FROM AUTHOR]

The Cenomanian-Turonian transition marks one of the most important extinction episodes of the Mesozoic era. This extinction event was associated with the development of widespread oceanic anoxia and pronounced stable carbon isotopic excursion. Despite its importance, the effects of the perturbation on higher latitude biotas, and from the Baltic region in particular, are currently underexplored. Therefore, in this contribution we present the fossil record of a foraminifera succession integrated with δ13C trends from two deep cores: Bliūdsukiai-19 from western Lithuania and Baltašiškė-267 from southern Lithuania. Two foraminiferal zones were distinguished: Rotalipora cushmani from the upper Cenomanian and Whiteinella archaeocretacea from the boundary strata between the Cenomanian and Turonian in the Baltašiškė-267 core section, and a W. archaeocretacea Zone in the Bliūdsukiai-19 core section. A chemostratigraphical analysis of the stable carbon isotopes revealed a positive Cenomanian-Turonian δ13C anomaly, with maximum values reaching 3.57‰ in the upper part of the Bliūdsukiai-19 core section. A non-metric multidimensional scaling analysis of the foraminifera communities revealed that the major changes in their assemblages were strongly temporally organized and associated with the changes in the stable carbon isotopic ratios. This fact points to the significant effects of the C-T extinction event on the northern Neotethys paleocommunities. [ABSTRACT FROM AUTHOR]

The upper Wenlock epoch (Homerian age) of the Silurian period was an interval of intense changes in biotic composition, oceanic chemistry and sea level, which also witnessed a double-peaked positive stable carbon isotopic excursion. These biotic and environmental perturbations are thought to have originated due to reorganizations of the ocean system and high-amplitude sea level fluctuations. However, the evolutionary responses of the size of the micro-phytoplankton, which would help comprehension of the oceanographic mechanisms of these global perturbations, are currently unknown. Therefore, in this contribution we present morphometric data on the size changes of cysts of the dominant acritarch genus Leiosphaeridia during the middle and upper parts of the Homerian, which includes the lundgreni and Mulde bioevents, from the deep shelf facies of the eastern Baltic Basin (western Lithuania, Viduklë-61 core). Three parameters were measured for size distributions. Those are namely: average size, range of sizes, and power law exponent, which measures degree of "heavy-tailedness" and thus complexity of the distribution of cyst sizes. The average of the cyst sizes increased in the post-lundgreni interval of the Homerian, which points to the fundamental shift in the acritarch communities. The uncovered trends in cyst size ranges and power law exponents of their cyst size distributions revealed their close correspondence to the 4th order sea level fluctuations. Probable paleoclimatic and paleoecological mechanisms for this connection are presented. [ABSTRACT FROM AUTHOR]

The Gėluva regional stage stratigraphically corresponds to the late Wenlock. This time interval witnessed significant graptolite extinctions and turnovers of conodont faunas, as well as a large positive Mulde carbon isotopic excursion. Thus, the development of a detailed stratigraphy is a necessary step in understanding the complex patterns of regional and global variations in the sediments accumulating during the time interval studied. Therefore, in this contribution we present a cyclostratigraphic analysis of gamma ray (GR) logs from four wells, which are located in the deep water facies belt of the Lithuanian part of the Silurian Baltic Basin of the Gėluva regional stage. The analysis was performed using REDFIT spectral estimation, continuous wavelet transform and signal filtering techniques. As a result two 4th order and five 5th order cycles were distinguished and named in all sections. The correlation of cycles between sections was calibrated with the graptolite biozones. The comparative analysis revealed that intra-basinal cyclostratigraphic correlation could achieve resolution of the order of several tens of thousands of years. [ABSTRACT FROM AUTHOR]

The Silurian period was a time of significant environmental change punctuated by a series of bioevents. The mid-Homerian lundgreni event was one of the most severe extinction episodes of the mid-Paleozoic, which mostly affected pelagic organisms, while simultaneously sparing benthos. Despite the great importance of phytoplankton in determining the causal mechanisms of ecosystem collapse, there are very few studies on the effects of the lundgreni event on this ecological super-guild. Here we present a detailed quantitative paleoecological analysis of the green algae and acritarchs of the upper Wenlock of the Viduklė-61 section (Western Lithuania). Independent high-resolution graptolite biostratigraphic and δ 13 C chemostratigraphic control ensures accurate calibration of the micro-phytoplankton diversity and community compositional trends. The constrained clustering and assemblage zoning revealed five distinct assemblages separated by sharp changes in genus diversity and sample taxonomic composition. The statistically estimated local genus richness curves revealed similarity with previously determined 4th order sedimentary cycles. Interestingly, though, it appears that the lundgreni (mid-Homerian) biotic event had a significantly smaller effect on the studied ecological super-guild than the subsequent mid-upper Homerian regression. [ABSTRACT FROM AUTHOR]

The Ireviken event was one of the most intense extinction episodes that occurred during the mid-Paleozoic era. It had a strong global effect on a range of clades, with conodonts, graptolites and chitinozoans affected most. Using geophysical proxies and conodont species parameters of their temporal abundance structure we investigate how they affected the selectivity of conodont species survival during this calamity. After performing bivariate logistic analyses on 34 species of conodonts, we find three variables that were statistically significantly associated with their odds of survival. These namely include spectral exponents that describe degrees of autocorrelation in a time series, the skewness of species abundance distribution, and average environmental preferences, which are mostly determined by ancient water depths at sampling sites. Model selection of multivariate logistic models found the best model includes species local abundance skewness and substrate preference. A similar pattern is revealed through the regression tree analysis. The apparent extinction selectivity points to a possible causes of environmental deterioration during the Ireviken event. The significant positive relationship between extinction risk and preferential existence in deeper environments suggests the open ocean causal mechanisms of biotic stress that occurred during the Ireviken event. Marine regressions, which were previously suggested as a causal factor in this extinction episode, on theoretical grounds should have had higher impact on species living in near-shore environments, through the processes of habitat loss which are associated with decreases of shelfal areas. In addition, the significant positive correlations found between skewness of abundance distributions and spectral exponent values and the probability of species survival suggest that community and ecosystem processes (which controlled species abundance fluctuation patterns) were significantly related to selectivity processes of this smaller mass extinction event. [ABSTRACT FROM AUTHOR]

Based on the integrated chemostratigraphic and lithostratigraphic studies, as well as biostratigraphic and palaeo-ecological analyses of conodonts in the Ledai-179 core, we present a combined model of change in the upper Wenlock and lowermost Ludlow strata of the inner shelf settings in the eastern part of the Baltic Basin. The comparison of the δ13C trend, and conodont and lithological successions confirms previous suggestions that the Birštonas and Nevėżis formations correspond to the Homerian. This is quite unexpected, however, that the chronostratigraphic position of the Širvinta Formation changed from the Gorstian to the upper part of the Homerian. The numerical biostratigraphic changepoint analyses of local conodont richness, per capita immigration and also per capita extirpation rates revealed several episodes of permanent change. These episodes of dynamic states either preceded or postdated the Mulde extinction interval at the beginning of the late Homerian δ13C excursion, which points to possible transient effects of this extinction event on conodonts. [ABSTRACT FROM AUTHOR]

J. Dalinkevičius was the first to establish the Stipinai Regionai stage in 1939. The name is after the Stipinai Village located in the northern Lithuania. The stratotype is in the Mūša River outcrop between Petrašiūnai and Svobiškės villages. The Petrašiūnai ąuarry is in the Petrašiūnai Village, which belongs to the Pakruojis District. The Stipinai Regionai stage is cropping out in some parts of the ąuarry and its thickness varies from 3 to 9 m. Production of dolostone in the Petrašiūnai ąuarry started in 1959. The largest amounts of dolostone were excavated in 2008. [ABSTRACT FROM AUTHOR]

Integrated lithostratigraphical, cyclostratigraphical, graptolite and conodont biostratigraphical and chemostratigraphical (δ13C) data are presented from the upper Jaagarahu, Gėluva and Dubysa regional stages, including thelundgreniEvent (middle Homerian) in the Viduklė-61 well, Lithuania. The Viduklė-61 well is located in the west of Lithuania in the deep-water facies zone. Because of its completeness, this section is the “keystone” for middle–upper Homerian stratigraphy that allows us to combine different kinds of data into a coherent picture of large-scale biotic and environmental turnover. Three formations are distinguished: the upper part of the Riga Formation, with the Ančia Member in the uppermost part, the Siesartis Formation and the lower part of Dubysa Formation. The Grötlingbo bentonite is in the upper part of Ančia Member. In the Gėluva regional stage, two 4th-order and six 5th-order cycles have been distinguished. In the studied interval of the Viduklė-61 core, the following graptolite biozones were recognized:lundgreni(upper part),parvus,nassa,praedeubeli,deubeli,ludensisandnilssoni(lower part). Conodonts enabled recognition of thebohemica longaBiozone. A single find ofCtenognathodus murchisoniPander in thenassagraptolite interzone indicates an earlier than previously thought origin of this species. [ABSTRACT FROM AUTHOR]

Machaerids are a branch of Lophotrochozoans closely related to the Annelids known from the Early Ordovician to the Mid Permian marine environments. One specimen of machaerid sclera was found in the Viduklė-61 well, Siesartis Formation, at the depth of 1 285.1 m. Along with the specimen, the graptolite species of Colonograptus deubeli (Jaeger) was found, which is a mark of the Late Homerian, Gėluva Age. Brachiopod fauna shows that at this time there was an anaerobic, low turbulence and low shelf marine environment, i. e. BA 4-5 zone of the benthic brachiopod assemblage. Machaerid studies have shown that it belongs to the Plumulites genus. Without a full animal print with all sclerites we cannot accurately describe these fossils. This is the first specimen which was found in Lithuania, Gėluva Regional Stage. This finding will give more information about fauna recovery after extinction in the Early Gėluva Regional Stage, also known as the ludgreni Event. With the help of machaerid findings, we also could reconstruct palaeoenviroments and autecology. [ABSTRACT FROM AUTHOR]

This article presents a dataset of geochemical analyses from Silurian altered volcanic ash beds (bentonites) characterising 132 eruptions and preserved in sedimentary sections of the East Baltic area. TiO2, Nb, Zr, Th, Y, Ce, Cr and V ratios with Al2O3are used for identifying correlations between ash beds from Scandinavian sections. Some correlated ash beds are illustrated by schematic maps of areal distribution indicating volcanic sources from directions of both Iapetus and Rheic palaeo-ocean margins. [ABSTRACT FROM AUTHOR]

Graptolites are a group of extinct colonial invertebrate organisms, which belong to hemichordates. They are the most important organism group of Silurian biostratigraphy in Lithuania. A lot of new material appeared recently that made possible the potential for the improvement of the graptolite biozonation of Lithuanian Silurian. In Lithuania graptolites are distributed from Coronograptus cyphus (upper Ruddanian) to Neocolonograptus lochkovensis (lower Pridolian). The intervals of Rhuddanian--Aeronian, Telychian--Sheinwoodian, Gorstian--Ludfordian and Ludlow--Pridoly boundaries are still problematic in Lithuania and further studies are necessary. [ABSTRACT FROM AUTHOR]

Copyright of Geologija is the property of Lithuanian Academy of Sciences Publishers and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Mulde event of the Late Silurian greatly disrupted the diversity and morphology of planktic biota. Among the affected groups were the chitinous acritarchs, which experienced a major shift in diversity and size distribution, and the monograptid graptolites, which were reduced to just one species. A consequence of the bottlenecking of monograptids was the inheritance of thickened rings of chitin, referred to as "sicular annuli", by descendants of the surviving Pristiograptus dubius stem lineage. These annuli remain present throughout the Ludlow and Přidoli, fluctuating in numbers between 0 and 8 per sicula until the start of the Saetograptus leintwardinensis biozone, at which point the number of sicular annuli is fixed at 3 across all monograptid taxa. Especially curious is the presence of a short interval during the Colonograptus praedeubeli and Colonograptus deubeli biozones wherein almost all siculae are devoid of annuli, before regaining them again at the end of the interval. This ring-less interval is concurrent with a major drop in acritarch abundance and increase in acritarch size and evenness. The interpretation of acritarchs as a primary food source for graptolites may provide some explanation for the shifts in the number of sicular annuli in the latter group. The excess chitin consumed from an acritarch-heavy diet provides a structural and ecological basis for the development of sicular annuli. The increase in average size during the praedeubeli-deubeli interval would mean a reduction in surface area, and therefore consumed chitin, for an amount of acritarchs with the same nutritional value. This would have extinguished the consumption of excess chitin in this period, temporarily arresting the development of sicular annuli. [ABSTRACT FROM AUTHOR]

The Ludlow epoch of the Silurian period was a time of significant geobiological perturbations, the most significant being the mid-Ludfordian Lau Event and associated huge positive carbon isotopic excursion. On the other hand, the impact of the Lau Event on ecosystems is far from understood, with the majority of studies being concentrated on conodonts, graptolites, and brachiopods. Therefore, here we present the high-resolution Gorstian to mid-Ludfordian Baubliai-2 core section record of the phytoplankton (acritarch and green algae) change from the deep shelfal facies belt of the Silurian Baltic Sedimentary Basin. Seven distinct phytoplankton assemblages are distinguished. The general feature of the assemblage change is an overarching trend toward higher relative abundances of the green algae disaster taxon Leiosphaeridia spp., which peaked during the Lau Event. The absolute abundance variability of the various components of the plankton including the hyper-abundant Leiosphaeridia spp. and Tasmanites spp. revealed the presence of consistent 0.93 Ma cyclicity. The diversity of phytoplankton is directly correlated with graptolite species diversity, which suggests common driving mechanisms of evolution for different components of the plankton community. The recurrence and joint recurrence plots and recurrence quantification analysis revealed a coordinated evolution of phytoplankton and graptolite diversities. The Lau Event interval stood out as a distinct coordinated low diversity state in both phytoplankton and in graptolites. Similar anomalous community states were previously detected in benthic communities (brachiopods), and in communities of pelagic predators (conodonts). Therefore, the current evidence suggests that the Lau Event had a significant impact across the whole range of communities and ecosystems. • The relative abundance of a "disaster taxon" Leiosphaeridia spp. increased with time during Ludlow, peaking during Lau Event. • The dynamics of absolute abundance of different plankton groups was driven by 0.93 Ma cyclicity. • The dynamics of diversity in phytoplankton and graptolites were directly correlated. • Lau Event represented coordinated low phytoplankton and graptolite diversity state, anomalous in Ludlow Epoch context. [ABSTRACT FROM AUTHOR]

The Pridoli epoch is one of the most geobiologically unstable intervals in the Silurian period. However, the ecological and evolutionary dynamics of the biota from this time are still poorly understood. Here we present a comprehensive quantitative time-series analyses of conodont abundances during the middle and the upper parts of the Pridoli epoch. The study reveals that the stratigraphic series of conodont abundances has a multifractal structure. This feature implies the presence of multiple serially correlated processes hierarchically operating on different time scales and interacting in a multiplicative fashion. Estimation of a maximal Lyapunov exponent and a test for presence of determinism also revealed a chaotic and non-linear low-dimensional nature of long-term conodont abundance dynamics. The most probable (but not exclusive) mechanism for the origin of chaos in the time series of conodont abundance is that conodont abundances tracked changes in crucial environmental parameters, most probably related to the climate that exhibits long term chaos. The complex and non-linear nature of the conodont dynamics is also revealed by a moving-window correlation analyses of conodont abundances and by an environmental proxy time series. We found three alternating episodes of different correlation patterns between conodont abundances and the o13C record. In the middle and upper most Pridoli interval there are positive but statistically non-significant correlations between these two variables. In contrast the lower part of the upper Pridoli (middle of the Jura formation) exhibits negative and statistically significant correlation between the variables. In addition moving-window standard deviation analyses reveals that during the transitions between these episodes, there were abrupt changes in the variance in both the carbon isotopes and the conodont abundances, which implies that these episodes represent alternative states in the way the earth system functioned that were punctuated by the critical transitions between them. The interval with negative correlations between abundances and isotopes was also marked by a profound evolutionary turnover of acanthodians and to lesser extent conodonts. This interval most probably represented an anomalous time, with differing ecological rules and increased macroevolutionary rates, which can be interpreted as a turnover pulse. The spectral cyclostratigraphic analyses of the abundance data reveals that conodont abundances also exhibited periodic oscillations at several frequencies. The cycles determined for the analysis have the period lengths of 56, 99, 127 and 950 Ka, which probably were caused by the periodic changes in the obliquity and eccentricity of Earth's orbit. The proposed proximate mechanism that controlled cyclic changes in the abundances of conodonts, based on the climatological deductions, was a variation in nutrients supplies that was due to changes in the degree of seasonality in the tropics, driven by Milankovitch cycles. It is probable that the described state shifts in the way that the ecosystem functioned were also forced by long-term Milankovitch cycles. [ABSTRACT FROM AUTHOR]

Gothograptid retiolitines were distinctive in being one of the very few graptolite groups to thrive through the late Wenlock extinction event that killed off most graptoloid species, and their distinctive construction may have been a factor in this success amid environmental adversity. New and rich material from two localities in Poland and five localities in Lithuania contains Gothograptus nassa, Gothograptus obtectus and four new species. The detailed morphology and reconstruction of the tubarium shows its specific features, different from other lundgreni Biozone retiolitines. The tubarium is narrow, elongated, finite, massive and compact. The thecal orifices are hidden by simple hoods or by extraordinary reticulated veils, which may cover the ventral walls. The colonies of Gothograptus species from the lundgreni Biozone are short, usually having eight pairs of thecae, whereas species from the post-lundgreni interval may reach more than 20 pairs of thecae. A common feature of Gothograptus species is the presence of singular genicular structures tightly covering thecal orifices. Reticulated hoods and veils are characteristic of species from the lundgreni Biozone. The most common such structures are nassa hoods, located on the proximal thecae in some species from the lundgreni Biozone, and on every theca of post-lundgreni species. Only Gothograptus domeyki n. sp. has no genicular processes on most thecae. Within a total of four species from the lundgreni Biozone and three species from the nassa and praedeubeli Biozones, we describe here the new species Gothograptus domeyki and Gothograptus velo from the lundgreni Biozone, Gothograptus diminutus from the parvus/nassa Biozone, and Gothograptus auriculatus from the dubius/nassa and praedeubeli biozones; G. auriculatus n. sp. is the youngest form of the genus Gothograptus. Variation within the genus Gothograptus during the post-lundgreni interval period is shown for the first time.