The ) is the longest period of the Paleozoic, which was characterized by a peak of greenhouse climate in Earth history, as well as extreme high sea level (Haq and Schutter, 2008;Munnecke et al., 2010), with warm and humid conditions in early-middle period and seawater temperature up to 45°C (Trotter et al., 2008). The carbon cycle fluctuated greatly (Melchin et al., 2013;Cramer et al., 2015) and atmospheric CO 2 concentrations reached ~4200 ppm. During the

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Forty-three graptolite species belonging to fifteen genera are described from the upper Katian ornatus and pacificus biozones and Hirnantian extraordinarius and persculptus biozones of Vinini Creek and Martin Ridge reference sections of north-central Nevada. Approximately half of the species described have not been previously recorded from Nevada, six species are left in open nomenclature. Infraorder Neograptina and Styracograptus gen. nov. are erected. The maximum graptolite diversity is in organic-rich black shale in the lower part of the pacificus Biozone in the Vinini Formation. Species diversity decreased abruptly at the top of the Diceratograptus mirus Subzone, recognized herein in the upper part of the pacificus Biozone. Faunal turnover reached a peak in the lower part of early Hirnantian extraordinarius Biozone where long-dominant Ordovician clades (diplograptines) are rapidly replaced by normalograptids (Neograptina), presumably evolved in, and invading from, a less-temperate higher latitude. Eight late Katian diplograptine species recur in the upper part of the extraordinarius Biozone but, in contrast to their former abundance, are present there only as very rare individuals. Even more unusually, eight diplograptine species (members of Dicellograptus, Anticostia, Rectograptus, Paraorthograptus, Phormograptus, Styracograptus and Appendispinograptus) also reappear in the uppermost part of the Vinini Creek section, well into the persculptus Biozone (which is topped by a prominent stratigraphic unconformity). These occurrences record a complex extinction pattern among graptolites that involved a radical but extended ecological reorganization rather than a synchronous global collapse of the pre-glacial ecosystem. The biozonation applied in the Nevadan sections correlates well with those established in the Yangtze Platform of China, southern Kazakhstan, north-eastern Siberia and Northern Canada. •

The shale-dominated hemipelagic succession exposed in the southwestern part of the Prague Synform preserves the most complete Ludfordian graptolite record so far encountered from peri-Gondwanan Europe. Four graptolite biozones -the Neocucullograptus inexpectatus, Nc. kozlowskii, Pseudomonoclimacis latilobus-Slovinograptus balticus and Pristiograptus fragmentalis biozones -are recognized in the middle and late Ludfordian, between the Bohemograptus tenuis Biozone and the base of the Pridoli Series. Conodont occurrences are restricted to scattered limestone beds, but enable tentative integration of the graptolite and conodont biozonal schemes. Particular attention was paid to faunal and sedimentary changes and the carbon isotope record across the middle Ludfordian Kozlowskii extinction Event. The Kozlowskii Event caused the almost simultaneous extinction of graptolites with ventrally curved rhabdosomes. The genera Bohemograptus, Polonograptus and Neocucullograptus, along with Pseudomonoclimacis dalejensis, disappeared from the fossil record. The offshore conodont fauna recorded in the section was not strongly affected and similarly the pelagic orthocerids and nektonic Ceratiocaris passed unaffected through the extinction interval. The abundant and widespread pelagic myodocopid ostracod Entomis, however, became extinct. The late Ludfordian graptolite recovery gave origin to a novel fauna of Pridoli type from taxa that emerged or just reappeared above the Kozlowskii crisis. In Všeradice and elsewhere in the Prague Synform, the recovery, manifested by the appearance of Pseudomonoclimacis latilobus and Slovinograptus balticus, closely postdates the end of the isotope excursion but pre-dates the first appearance of the conodont index 'Ozarkodina' snajdri. Here the graptolite recovery was delayed relative to the recovery of the benthic fauna. A canalized intraformational limestone conglomerate corresponds with a gap in the sedimentary record above the Kozlowskii extinction and just below the graptolite recovery. The benthic faunas from the conglomerate matrix and pebbles permit correlation with the shallower part of the basin indicating a distinct fall in sea-level. The present data demonstrate the coincidence of the graptolite crisis with benthic faunal change and eustatic fall in sea-level manifested by facies change and the carbon isotope excursion. Polonograptus chlupaci sp. nov., from the Nc. kozlowskii Biozone, is described and several other graptolite taxa are redescribed.

Study of the lower Silurian black shale succession of the Prague Synform has enabled detailed insight into graptolite faunal dynamics and diversity trends from the mid-Aeronian diversity maximum through to the late Aeronian crisis. Graptolite diversity decreased from 33 taxa in the Lituigraptus convolutus Biozone to 17 taxa in the upper part of the Stimulograptus sedgwickii Biozone and newly erected Lituigraptus rastrum Biozone. The graptolite assemblages of the latter biozones exhibit low species richness along with high dominance. Many graptolite species that became extinct in the early part of the sedgwickii Zone were promptly replaced by new forms. In the later part of the sedgwickii Zone, however, replacement of extinct species by new forms considerably decelerated. The increased rate of graptolite extinction recorded in the convolutus-sedgwickii biozone boundary beds coincided with subtle changes in black shale lithologies and a positive shift in δ 13 C org (of 2.2 ‰) compared to baseline values. Sea-level drawdown can be inferred from siltstones and/or temporary nondeposition in the middle sedgwickii Zone. This level also sees total organic carbon (TOC) fluctuations and a strong positive δ 13 C org excursion with a peak shift of at least 7 ‰. The sedgwickii Event exhibits substantial reorganization of the graptolite fauna, its taxonomic impoverishment and concomitant increase in species dominance rather than a sudden collapse of the pre-extinction assemblage. Associated changes in lithology, TOC and the pronounced δ 13 C org excursion suggest a relatively extended and probably multi-phase period of stressed conditions that affected the pelagic realm inhabited by graptolites in the course of the late Aeronian interval.

Nearly 50 sections through the Llandovery and Wenlock black shales of the Barrandian area (Bohemia) have been examined bed by bed. This has made possible the compilation of an improved and well defined graptolite zonal scheme with much new biostratigraphic data included. A total of 268 graptolite species and subspecies have been found. Their stratigraphic distribution allows the recognition of 27 graptolite zones:

The Hirnantian and Llandovery sedimentary succession of the Barrandian area has been assigned to middle and outer clastic-shelf depositional settings, respectively. Deposition was influenced by the remote Gondwanan glaciation and subsequent, long-persisting, post-glacial anoxia triggered by a current-driven upwelling system. High-resolution graptolite stratigraphy, based upon 19 formally defined biozones-largely interval zones-and five subzones, enabled a detailed correlation between 42 surface sections and boreholes, and enabled linking of the sedimentary record, graptoloid fauna dynamics, organic-content fluctuations and spectral gamma-ray curves. The Hirnantian and Llandovery succession has been subdivided into four biostratigraphically dated third-order sequences (units 1-4). Time-spatial facies distribution recorded early and late Hirnantian glacio-eustatic sea-level lowstands separated by a remarkable mid-Hirnantian rise in sea-level. A major part of the post-glacial sea-level rise took place within the late Hirnantian. The highstand of Unit 2 is apparently at the base of the Silurian succession. Short-term relative sea-level drawdown and a third-order sequence boundary followed in the early Rhuddanian upper acuminatus Zone. Early Aeronian and late Telychian sea-level highstands and late Aeronian drawdown of likely eustatic origin belong to units 3 and 4. Sea-level rise culminated in the late Telychian, which may also be considered as a highstand episode of a second-order Hirnantian-early Silurian cycle. Facies and sequence-stratigraphic analysis supports recent interpretations on nappe structures in the core part of the Ordovician-Middle Devonian Prague Synform of the Barrandian.

The taxonomy and biostratigraphy of the Aeronian graptoloid graptolites of the Tanezzuft Formation (Murzuq Basin and Al Qarqaf Arch area) is presented and discussed with respect to their palaeoenvironmental setting and palaeobiogeographical links. The gregarius-libycus, 'leptotheca', convolutus and sedgwickii assemblage biozones and tenuis Subzone are recognized and correlated with the generalized zonal scheme and with graptoloid successions in periGondwanan Europe. The Rhuddanian ⁄ Aeronian boundary is tentatively placed at the base of the gregarius-libycus Biozone. Telychian faunas have not been identified. Fourteen of the 23 species recorded herein belong to the middle Aeronian convolutus Biozone assemblage. The overall low diversity may be the result of inhabiting unstable, occasionally turbulent and ⁄ or oxic environments. The lowest diversity, but with abundant graptoloid rhabdosomes, is observed in proximal silty and sandy deposits. The presence of 'Paraclimacograptus' libycus suggests biogeographical links to Aeronian graptolite faunas of Jordan and South America. The convolutus Zone assemblage is very similar to the coeval faunas of the Saudi Arabian Qusayba shales. The occurrence of several species endemic to northern and north-western Gondwana and peri-Gondwana provides further evidence for a distinct palaeoclimatic ⁄ palaeolatitudinal control on graptolite distribution.