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Ordovician rocks extensively border and cover Laurentia or the North American Craton in Canada. These rocks represent diverse and significant successions spread across a variety of depositional and palaeogeographic settings in the Canadian Arctic Islands, Eastern Canada, Western Canada and the Canadian Interior. During much of the Ordovician, Laurentia straddled the palaeoequator and was flooded by extensive epicontinental seas, experiencing high temperatures and high faunal diversity. The central and western parts of the Laurentian Craton remained relatively stable during the Ordovician, but there was substantial tectonic activity with the Taconic Orogeny affecting the Appalachian area and the Pearya composite terrane affecting the Franklinian Margin along its eastern and northern margins, respectively. The large Hudson Bay and Williston basins and smaller satellite basins cover the cratonic interior in Canada. These shallow intracratonic basins, dominated by marine carbonates with some evaporites, are the erosional remnant of a more extensive sea episodically connected with the adjacent platformal areas during the Ordovician. The Global Boundary Stratotype Section and Point (GSSP) for the base of the Ordovician System is exposed in Green Point, western Newfoundland while the Ordovician–Silurian boundary interval is well exposed on Anticosti Island, Québec but is also present in Ontario, Manitoba, Yukon and Arctic Canada.

Anticosti Island, eastern Canada, records an exceptionally thick and well-exposed Ordovician/Silurian boundary section that hosts a series of diverse marine invertebrate faunas across the Late Ordovician mass extinction. However, the base of the terminal Ordovician stage, the Hirnantian, has been difficult to identify on Anticosti due to the lack of a traditional Hirnantia fauna within the Upper Ordovician Ellis Bay Formation. Previously, the eponymous taxon of the Hirnantia fauna, and type species of the genus Hirnantia, H. sagittifera (M'Coy, 1851) has been reported only from the uppermost Ellis Bay Formation, leading to uncertainty as to the age of the lower Ellis Bay Formation. Here we report Hirnantia notiskuani n. sp. from the lowermost Ellis Bay Formation. This new species is similar to the type species, H. sagittifera, but is distinguished by its strongly dorsibiconvex shell in mature forms and variously developed uniplicate anterior commissure. Occurrences of these two similar species of Hirnantia, H. notiskuani and H. sagittifera, within the lower and uppermost Ellis Bay Formation, respectively, indicate a Hirnantian age for the entire Ellis Bay Formation, a finding that is supported by recent palynological and chemostratigraphic studies. Brachiopod assemblages within the Ellis Bay Formation therefore are best characterized as a unique and diverse Hirnantia fauna, consisting of genera from both the typical Hirnantia fauna and the epeiric seas of Laurentia.UUID: http://zoobank.org/1c1dff6a-ee38-4cd3-b8bd-3d803a2774ef

Platymerella from the lower Red Mountain Formation in Georgia and Tennessee, the Bowling Green Dolomite of west-central Illinois, and the Elwood Dolomite of northeastern Illinois represents a paleosubtropical, cool-water occurrence of virgianid brachiopods in Laurentia during the early Silurian (middle–late Rhuddanian). These occurrences were located in the southern Appalachian foreland basin and the distal end of the Sebree Trough, likely subjected to frequent cool-water current and upwelling from Gondwana. Compared with broadly coeval species of Virgiana from lower paleotropical to equatorial latitudes, Platymerella has significantly smaller, dorsoventrally flattened shells, with subequal ventral and dorsal umbones and beaks that extend only slightly above the hinge line. Relative to its shell size, however, Platymerella has more prominent thickening of the shell wall, median septum, spondylium, and hinge plates than Virgiana, resembling more closely the extravagant shell thickening of Tcherskidium and Proconchidium from the Late Ordovician (late Katian) equatorial regions. The thickening of hinge plates resulted in the formation of a pseudocruralium, which separates Platymerella from Virgiana. In latest Ordovician–earliest Silurian virgianids, there was a general morphological gradient toward a smaller shell, reduction in the ventral-valve convexity, and reduction in the size and height of the ventral umbo from paleoequatorial to southern subtropical regions, with Platymerella representing the most southerly forms.

The Late Ordovician (late Katian) Tcherskidium fauna consisted of large- and thick-shelled virgianid pentamerid brachiopods characterized by large and ribbed shells of Tcherskidium and Proconchidium and usually associated with Holorhynchus, Deloprosopus, and Eoconchidium. This unique fauna was widely distributed across several tectonic plates, largely confined to the paleoequatorial and especially the northern paleotropical zones, such as northern Laurentia, accretionary terranes of Alaska, Kolyma, Baltica, Siberia, Kazakh and adjacent terranes, and South China. In Laurentia, the eponymous genus Tcherskidium was predominant in regions north of the paleoequator and, in sharp contrast, was absent south of the paleoequator. In this study, Tcherskidium lonei n. sp. and Proconchidium schleyi n. sp. are described from Alaska and North Greenland, respectively, adding new data on the Tcherskidium fauna of the Late Ordovician Northern Hemisphere. Shell gigantism, together with the sharp paleobiogeographic division, suggests that the Late Ordovician (late Katian) Northern Hemisphere had a prevailing warm-water mass, probably due to the lack of large landmass beyond the northern tropics. This was in sharp contrast to the Southern Hemisphere, which was frequently influenced by cold-water invasions from the ice-bearing Gondwana supercontinent centered on the South Pole.UUID: http://www.zoobank.org/25d9b772-bd7d-4ad6-bfc6-ba02b1567cf3

Epipunctae are microscopic perforations that do not penetrate the shell but are confined to the outer layers of the shell. They have been known previously only in the orthidine family Plaesiomyidae. The striated walls of epipunctae are considered unique to brachiopods and thus of significance for the study of stem-group brachiopod. In this study, we report the first occurrence of epipunctae in a non-plaesiomyid brachiopod based on a well-preserved external mould of Cathaysiorthis yushanensis from the lower Silurian Shiyang Formation of Jiangxi, southeastern China. The species belongs to the Family Cathaysiorthidae which differs from the Family Plaesiomyidae in many aspects especially in dorsal internal structures. The new data imply that epipunctae may be more widespread in orthide brachiopods than previously thought, strengthening the notion that this is a plesiomorphic character of the brachiopod shell. The discovery of epipunctae, however, depends on excellent preservation of the outer surface of the shells as well as careful cleaning and observation.

A Late Ordovician brachiopod fauna from the Black River quadrangle (D-1 1:63,360 scale) of east-central Alaska comprises taxa typical of the Late Ordovician brachiopod fauna in the pericratonic epeiric seas of Laurentia, including Hesperorthis pyramidalis (Twenhofel, 1928), Plaesiomys occidentalis (Okulitch, 1943), Eoplectodonta sp., Holtehdalina sp., Leptaena sp., Brevilamnulella minuta n. sp., Tcherskidium tenuicostatum n. sp., Rhynchotrema iowense Wang, 1949, and Whitfieldella sp. The presence of Plaesiomys occidentalis and Tcherskidium tenuicostata n. sp. indicates a latest Katian age by correlation with similar species in the Mackenzie Mountains, southern Manitoba, Anticosti Island, the American midcontinent, Kolyma, and Siberia. Cluster analysis based on 20 well-studied late Katian brachiopod faunas from various regions within Laurentia and elsewhere in other tectonic plates suggests that the small brachiopod faunule from Alaska has the strongest paleobiogeographic affinity with Laurentia, confirming that the Black River quadrangle of Alaska was part of Laurentia during the Late Ordovician.UUID: http://zoobank.org/6b387856-61d5-4685-a592-faf5287c1e0f

Dalmanelloid brachiopod shells were collected from the Upper Ordovician Lexington Formation (lower Katian) of Kentucky, Sheguindah Shale (middle Katian) on Manitoulin Island, Ontario, and the Stony Mountain Formation (upper Katian) in the Winnipeg area, Manitoba. They were investigated to test the hypothesis of paleo-latitudinal zonation of the shelly benthos. A multi-technique approach was applied to evaluate the petrographic and geochemical (isotopic and elemental) preservation of the secondary layer of shells. Preliminary conventional microscopy, cathodoluminescence (CL), and scanning electron microscopy (SEM) confirmed the retention of primary shell ultrastructure (prismatic low-Mg calcite). The geochemical diagenesis proxies (e.g., Sr, Mn, Fe, and ΣREE) show insignificant correlations with the δ18O and δ13C values, thus supporting the preservation of at least near-primary geochemical compositions. Among the three lots of shells, the mean δ18O value is the highest in those from the Lexington Formation (–4.5‰ ± 0.3‰ VPDB), lowest from the Stony Mountain Formation (–6.8‰ ± 0.4‰ VPDB), and intermediate from the Sheguindah Shale (–6.0‰ ± 0.8‰ VPDB). The relative gradient in δ18O increase is in agreement with the paleo-latitudinal gradient, with Kentucky in subtropical, southern Ontario in mid-tropical, and southern Manitoba in subequatorial latitudes. The Lexington Formation shells also have the highest mean δ13C value (0.8‰ ± 0.2‰ VPDB) and relatively high P contents (170 ± 27 ppm), suggesting higher organic productivity, which is consistent with previous interpretation of frequent upwelling of nutrient-rich cool waters along the southeastern margin of Laurentia during the Katian. The Lexington shells also have a lower mean Th/U (0.6 ± 0.6), which is consistent with blooming organic productivity that likely led to more consumption of oxygen in the water column.

The end Ordovician mass extinction (EOME) was the second most severe biotic crisis in Phanerozoic, and has been widely linked to a major glaciation. However, robust geochronology of this interval is still lacking. Here we present four successive high-precision zircon U–Pb dates by isotope dilution thermal ionization mass spectrometry (ID-TIMS) for biostratigraphically well-constrained K-bentonites of a continuous Ordovician-Silurian boundary section at Wanhe, SW China. They include 444.65 ± 0.22 Ma (middle Dicellograptus complexus Biozone), 444.06 ± 0.20 Ma (lower Paraorthograptus pacificus Biozone), 443.81 ± 0.24 Ma (upper Tangyagraptus typicus Subzone), and 442.99 ± 0.17 Ma (upper Metabolograptus extraordinarius Biozone). Calculations based on sedimentation rates suggest a duration of 0.47 ± 0.34 Ma for the Hirnantian Stage, which is much shorter than previously thought (1.4 ± 2.05 Ma in the International Chronostratigraphic Chart ver. 2019/05). The new data also constrain the Hirnantian glacial maximum to ∼0.2 Ma, supporting that its brevity and intensity probably triggered the EOME. Keywords: ID-TIMS, K-bentonite, End Ordovician mass extinction (EOME), Hirnantian stage

Network and frequency distribution analyses of global brachiopod occurrences in the earliest Silurian (Rhuddanian–Aeronian) revealed that brachiopod recovery from the end-Ordovician mass extinction during the early–late Rhuddanian was represented mainly by the reestablishment of Late Ordovician cosmopolitan holdover taxa. Brachiopods nearly doubled their generic diversity from Rhuddanian to Aeronian, owing to the radiation of both endemic and cosmopolitan taxa, associated with an overall post-glacial amelioration of global environment and increased habitat heterogeneity as a result of marine transgressions and expansion of epeiric seas. A drastic turnover from the Ordovician-type to Silurian-type brachiopod faunas took place in the Aeronian, several million years after the terminal Ordovician mass extinction. Compared with the orders of orthides and strophomenides that radiated and predominated in the Ordovician, the atrypides and pentamerides displayed pulses of drastic diversification from the Rhuddanian to Aeronian, mainly in tropically located paleoplates, to become the most abundant and diverse brachiopod orders in the Silurian. Atrypides recovered in the early Rhuddanian, whereas diversification of pentamerides was delayed until the Aeronian and becoming widespread in South China, Kazakhstan terranes, Baltica, Avalonia, and Laurentia.

During the late Sandbian and early to middle Katian, a major marine transgression flooded the intracratonic basins and platforms of eastern North America, allowing brachiopods to disperse into the newly formed epicontinental seas. Two main brachiopod faunas can be differentiated using multivariate analysis of faunal data from localities across Laurentia during this time: a relatively diverse Scoto-Appalachian Fauna confined to the eastern margin of North America and peri-Laurentian terranes, and a less diverse but more widely distributed Epicontinental Fauna that expanded into the remainder of the flooded continent. The Epicontinental Fauna can be divided into four subfaunas with subtle compositional differences that correspond to different paleoenvironmental settings of eastern North America, influenced by such paleoecological factors as nutrient-rich cool-water upwelling onto the continent through the Sebree Trough, a greater range of habitable environments on the continental margin and in the adjacent deep Taconic foreland basin, and the interactions between pericratonic and intracratonic water masses of different physical and chemical properties. The Epicontinental brachiopod faunas dominated basins and platforms of continental interior until the Hirnantian extinction event.

Ziegler's (1965) early Silurian brachiopod community zones and Boucot's (1975) Benthic Assemblages have been instrumental in determining the community structures of early–middle Paleozoic level-bottom communities, but are difficult to apply to reef ecosystems due to the mixing of level-bottom community assemblages in these systems. In this study, Shannon and Simpson diversity levels were calculated for reef-dwelling brachiopod faunas from several North American and one European localities. Reef-dwelling brachiopod diversity collapsed at the end of the Ordovician and did not recover until the mid-Aeronian when modest diversity reef faunas appeared in the higher tropics. Reef-dwelling brachiopods did not achieve high diversity levels until the Telychian when reefs invaded the paleoequatorially located Hudson Bay and Moose River basins. The Attawapiskat Formation (Telychian) contains the earliest known coral-stromatoporoid reef complex with associated high-diversity brachiopod faunas. These faunas were separated into nine community associations through clustering and principal component analyses. These associations can be further grouped into a level-bottom-type and a cryptic-type based on dominant brachiopod taxa, diversity levels, average shell size, and substrate type. Surprisingly, the large species Pentameroides septentrionalis was able to thrive in the relatively flat and open spaces of inter-reef areas and among frame-building corals and stromatoporoids within reef cores. The absence of Stricklandia within the Attawapiskat Formation is due to the high water temperature of the equatorial seas which were too warm to be invaded by this cool-water dependent genus. In addition, the presence of deep-water Clorinda and Gypidula in the shallow-water Attawapiskat reefs is explained by the lack of hurricane-grade storms in the equatorial region, which would be comparable to the quiet-water conditions below storm wave base in higher latitudes.

The subfamily Hindellinae is an early group of athyride brachiopods, characterized by a simple jugum that connects the laterally directed spiralia, which are disjunct from the crura. Four genera (Hindella, Cryptothyrella, Koigia, and Hyattidina) are reexamined on the basis of their internal structures, such as the crura and their connection to the hinge, the jugum, and spiralia. The internal brachidium and shell of the Aeronian genus Cryptothyrella differ substantially from those of Hindella. Elkanathyris pallula n. gen. n. sp. is recognized as a posteriorly ribbed hindellide of Aeronian age. These genera are transferred from the Meristellinae to the subfamily Hindellinae (family Hindellidae). On Anticosti Island, Hindella is confined to the Hirnantian (latest Ordovician): it became extinct at the end Ordovician during the last of several mass extinction events that also extinguished the Laframboise reefs at the top of the Ellis Bay Formation. Post-extinction recovery of athyrides was pioneered by small-shelled Koigia, which are abundant in the basal Silurian Becscie Formation. Hyattidina, with a simple brachidium, is abundant in the Aeronian and Telychian of Anticosti, but absent earlier. True meristellines, as envisioned here, first appeared in the Aeronian Gun River Formation. The revised taxonomy and stratigraphic ranges of these earliest athyrides shed light on the nature of the Ordovician–Silurian mass extinction and recovery, and help refine the biostratigraphy of the O-S boundary interval.

Karlsorusn. gen. is proposed in this study as a large, smooth-shelled pentameride brachiopod of the family Pentameridae, based onPentamerus gothlandicusLebedev, 1892, from the Wenlock (Silurian) Slite beds of Gotland, Sweden. This species is transferred fromPentamerusto the new genus because of the combination of aPentamerus-like shell shape and the development of a brachiophorium through fusion of the outer hinge plates in the middle portion, like a dorso-ventrally inversed cruralium. The first appearance of brachiophorium in pentamerids is in the late Wenlock, known also inBrooksina,Pentamerifera, and other related pentamerid genera, marking a significant stage in morphological transformation of dorsal internal structures, as part of the Silurian pentameride diversification in both level-bottom and reefal depositional environments.

Plectorthis is a commonly reported Late Ordovician brachiopod genus from Laurentia and several other tectonic plates. Examination of shells from the Cincinnati Arch type area shows that species previously assigned to the genus have a considerable range of variability, such as ribbing style, shell outline, and musculature. The type species, Orthis plicatella Hall, 1847 is characterized by generally simple costae, with double-rowed aditicules on each rib, and a cordate ventral muscle field. Some species previously attributed to Plectorthis have a subtriangular ventral muscle field and hence a closer affinity to the plaesiomyid genus Austinella . Orthis fissicosta is here demoted to a subspecies of Plectorthis plicatella based on its similar ribbing style to some specimens of the type species. In Laurentia, Plectorthis first appeared in the Darriwilian–Sandbian boundary interval, achieved a relatively high species diversity and wide paleogeographic distribution in pericratonic seas during the early Katian; the subequatorial species attained a notably larger shell than those in the higher paleotropics. The genus did not invade the intracratonic basins of Laurentia and became extinct by the late Katian.

The latest Katian (Late Ordovician) is marked by the third biodiversity climax of the Great Ordovician Biodiversification Event (GOBE) prior to the Late Ordovician mass extinction (LOME). In this study, the Chemical Index of Alteration (CIA) is used to determine the paleoenvironmental change recorded in the Arisu Member, the Siltstone Member, and the Sandstone Member of the Terekawat (= Tierekeawati) Formation (upper Katian) in the Tarim Basin, northwestern China. CIA values from these members are plotted in A–CN–K ternary diagrams respectively. Linear regression and 95% confidence interval estimation results indicate that these deposits were derived from the same parent rock, and the corrected CIA (CIAcorr.) values reveal significant paleo-climate changes during Late Ordovician. Sea-surface temperatures (SSTs) have been estimated by comparing 31 modern estuary systems. These data show that the CIAcorr. values dropped from 77.41 to 64.83, corresponding to an interpreted temperature drop from 20.5 to 10.2 °C in the Dicellograptus complexus graptolite Biozone of the upper Katian (Ka-4). CIAcorr. values varied within a range of 67.63–70.16, implying temperature fluctuations between 12.5 and 14.6 °C in the lower to middle Paraorthograptus pacificus Biozone. CIAcorr. values rose again from 69.09 to 76.05, corresponding to a temperature rise from 13.7 to 19.4 °C in the upper Paraorthograptus pacificus graptolite Biozone of the latest Katian. This is interpreted to be a cooling and warming cycle, corresponding to the mid-Boda cooling and the late-Boda warming events. This study suggests that the climate change during late Katian was more intense than previous thought, especially in subtropical zones of Paleo-Tethys. This cooling event enhanced the thermohaline ocean circulation and became one of the major factors causing the well-known late Katian faunal dispersal (i.e. the Boda event). Hirnantian glaciation would have further promoted global oceanic cooling, over-stressed the ecosystems, and triggered the LOME.

The Kettle Point Formation of southwestern Ontario consists of intervals of organic-rich interlaminated black shale interbedded with organic-poor greyish green mudstones and rare red beds, separated by metre-scale sequences of non-interlaminated black shale. The formation shows a largely consistent background value for the black shales around −20‰ δ34S, punctuated by a substantial positive excursion of ∼32‰ (up to +12.87‰) that coincides with a significant interval of greyish green mudstone and red beds. Lithological and geochemical data indicate that the black shales were deposited during periods of anoxia, with thick intervals of non-interlaminated black shales recording the peak of anoxia, whereas the greyish green mudstones record deposition in more oxygenated environments. Relative water depth is interpreted as the key control on the vertical and lateral distribution of the Kettle Point lithofacies. Interbedded black shales and greyish green mudstones were deposited in relatively shallow waters, where minor, short-lived falls in relative sea level promoted dysoxic to oxic conditions and the deposition of organic-poor lithologies. Non-interlaminated black shales are indicative of substantial rises in relative sea level, resulting in widespread anoxia and the deposition of thicker and more laterally extensive packages of organic-rich sediment. The formation of black shales in relatively shallow waters in southwestern Ontario implies that the extensive deposition of organic-rich sediment across eastern North America during the Late Devonian was a product of widespread anoxia related to restricted circulation in intracratonic and foreland basin depositional centers.

Pentameroides is a large-shelled pentameride brachiopod, which was widespread throughout Laurentia in the early Silurian (Telychian). Evolving from Pentamerus in the early Telychian, it dispersed from its subtropical – high tropical origin to subequatorial intracratonic seas by the late Llandovery. In this study, large collections of reef-dwelling Pentameroides septentrionalis from the Attawapiskat Formation, Akimiski Island, Nunavut, and level-bottom-inhabiting Pentameroides subrectus from the Fossil Hill Formation, Manitoulin Island, Ontario, and the Jupiter Formation, Anticosti Island, Quebec, were biometrically analyzed for seven external morphological features. Bivariate and ordination analysis (principal components analysis) revealed that P. septentrionalis has a more globose, more biconvex shell with a larger ventral umbo than P. subrectus. These morphological differences, coupled with their excellent preservation in shallow-water reefal environments, suggest that P. septentrionalis was adapted to a relatively low-turbulence, hurricane-free, nutrient-stressed environment near the equator (

The decimeter-scale 3-D network structure of the Upper Ordovician Pagoda Formation in South China has been an enigmatic sedimentary feature and a case of non-uniformitarian carbonate depositional system, without modern analog. The network bands are developed pervasively throughout the entire Pagoda Formation, superficially resembling desiccation or syneresis cracks, especially in bedding-plane view, with decimeter-scale sub-polygonal to irregularly sinuous patterns. Detailed petrographic analysis, however, shows that the crack-like network bands have the same carbonate matrix, skeletal grains, and overall fabrics as the rock they surround. In this study, we demonstrate that the network structure is not generated by shrinkage cracks but is rather a time-specific lithofacies. It originated from prolonged growth of nodular carbonate, controlled by the convergence of several geological and paleoclimatic factors, including a) a protracted sea-level highstand lasting for about 5 Myr, b) an interval of tectonic quiescence favoring the dominance of carbonate production, with minimal siliciclastic input, and c) location of the South China paleoplate in the hurricane-free paleoequatorial zone devoid of severe storm disturbances between the fairweather and maximum storm wave bases (normally 15–120 m depths), favoring long-term, uninterrupted growth of CaCO3 meganodules on a mid-shelf substrate. This study corroborates recent paleogeographic reconstructions that position the South China paleoplate on the Equator during the Late Ordovician.

Through a comparative study with the British type material, several dalmanelloid brachiopod species from the Upper Ordovician of the Cincinnati Arch area of North America (Laurentia) are now confirmed to belong to Heterorthina Bancroft. These include several species previously treated variously as Dalmanella or Onniella, including such classic and widely cited species as ‘Dalmanella’ emacerata (Hall) and Dalmanella fairmountensis Foerste. These North American forms of Heterorthina belong to the dalmanelloid clade that is characterized by a dorsal medial interspace, and of cool to cold-water origin. Outside of Laurentia, Heterorthina occurs predominantly in Avalonia and peri-Gondwanan terranes, such as Iberia (Spain), Armorica (France) and Bohemia, palaeogeographically located between 40° and 60° south. The episodic occurrences of several Heterorthina species in the lower to middle Katian of the Cincinnati Arch area, located around 20°S in the Late Ordovician, are interpreted as opportunistic invasions of a cool-water brachiopod fauna from higher palaeolatitudes, associated either with oceanic cooling events or with relatively cool deep-water mass incursions during marine transgressions.

The Great Ordovician Biodiversification Event (GOBE) laid the foundation for present-day biodiversity levels and set an agenda for marine life against a background of modern-type climates. The event was protracted, commencing at the beginning of the Ordovician and unfolding during 40 million years (myr) of the period. The first diversity acme (Tremadocian–Floian) was strongly diachronous across both the paleoblocks and groups of organisms. But within a 10 myr interval, during mainly the Middle Ordovician (Darriwilian), the global marine species richness was tripled, i.e., the second diversity acme. The third acme (Katian) was much more unified across both taxonomic groups and terranes. This diversification trend continued into the Silurian and Devonian making GOBE the most sustained marine biodiversity pulse of the entire Phanerozoic. The GOBE was also marked by three major faunal turnovers based on the brachiopod data, in the mid-Darriwilian, end-Katian, and end-Hirnantian, respectively. Each turnover was followed by an explosive radiation of new faunas, especially in the shallow-marine shelly benthos. Potential intrinsic or extrinsic drivers for this event are widely debated, but a causal narrative remains elusive.

Bivariate and multivariate analyses of well-preserved specimens of four species of the Ordovician–Silurian brachiopod genus Parastrophina from eastern North America, the Tarim Basin of Northwest China, and Kazakhstan revealed that the subelliptical shells of Parastrophina hemiplicata from southern Ontario are less globose than the subpentagonal shells of Parastrophina tarimensis n. sp. from the Tarim Basin. Parastrophina minor from Baffin Island has a subelliptical outline, similar to P. hemiplicata, but is more globose than the specimens from southern Ontario, although this increased globosity was due partly to increased convexity of ventral valve. Three specimens of Parastrophina iliana from Kazakhstan show features between the extreme forms of P. hemiplicata and P. tarimensis. These differences may be related to different paleoenvironmental settings — an enlarged dorsal valve in P. tarimensis would enable the development of larger lophophores at maturity for feeding and gas exchange in the generally low-energy, shallow-water carbonate mound settings in the paleoequatorially located Tarim Basin and Kazakhstan terranes, whereas a wider outline would increase stability on the high-energy, storm-influenced, flat-bottom substrates in the epeiric seas of southern Ontario, which was located in the subtropics during the Late Ordovician.

Preface for the special issue Ecosystem evolution in deep time: evidence from the rich Palaeozoic fossil records of China.

The oldest Foliomena fauna was, until now, known from the middle–upper Miaopo Formation (Nemagraptus gracilis Biozone, lower Sandbian, basal Upper Ordovician) of South China. In this study, the oldest record of the fauna is set back to the latest Darriwilian (upper Hustedograptus teretiusculus Biozone), represented by Foliomena jielingensis and some typical constituents of the Foliomena fauna from the basal Miaopo Formation at Jieling, northern Yichang, western Hubei Province, central China. The Miaopo Formation is characterized by its organic-rich dark-grey shale facies, unique in its localized distribution on the Yangtze Platform, and distinguished by its rich and diverse benthic and graptolitic faunas. This suggests an origin of the Foliomena fauna in periodically oxygen-starved local depressions on the Yangtze Platform during the Middle–Late Ordovician transition.

Paleobiogeographic patterns of the brachiopod faunas before and during the first radiation of the Great Ordovician Biodiversification Event (GOBE) in South China at 6 different localities from the upper Jiangnan Slope to the vast area of the Upper Yangtze Platform show several interesting features. First, the initial brachiopod diversity acme was accompanied by both high origination and extinction rates. Second, no significant changes took place in the taxonomic composition and paleobiogeographic pattern of the brachiopod fauna during the radiation at 5 of the 6 localities studied except the near shore locality, where the first brachiopod radiation was much later than at other localities and was marked by a dramatic increase in endemic constituents. Third, orthides were the predominant brachiopod group during the radiation, and regional brachiopod taxa played a significant role in defining the paleobiogeographic pattern of the radiation. Fourth, the first brachiopod radiation was associated with 3 major pulses of onshore migration from the upper Jiangnan Slope through the central Upper Yangtze Platform to the near shore settings of the platform, with the middle pulse being the most significant. Finally, paleogeographic dispersal took place in both onshore and offshore directions, although the onshore expansion was more prominent; several key brachiopods, such as Paralenorthis, Nocturnellia, Protoskenidioides, Nereidella, Euorthisina and Yangtzeella, first appeared on the upper Jiangnan Slope and later formed distinct, and taxonomically diverse, communities on the Upper Yangtze Platform. The paleogeographic dispersal of brachiopods is considered to be closely related to the tectonic evolution of the Qianzhong Arch.

In modern marine ecosystems, sea-grass and chlorophyte meadows play an important ecological role by serving as a carbon sink. Despite their generally limited areal distribution, the high productivity of sea-grass meadows makes them an efficient assimilator of CO2. During the early Palaeozoic, complex life was virtually confined to the marine environment, with algae being one of the common carbon-fixers, alongside abundant calcifying cyanobacteria, rhodophytes, chlorophytes and charophytes, as well as non-skeletal dinoflagellates and acritarchs. Fossil and molecular data indicate that marine thallophytic algae first appeared in the Early Proterozoic and became widespread in the Palaeozoic, although their fossil record is sporadic because of their soft-bodied nature; in the absence of angiosperm sea grass and mangroves and poorly understood phytoplankton biomass, thallophytic algae were probably major primary producers. In this article, we suggest that thallophytic algae may have played a significant role as a carbon sink in the Early Silurian, analogous to modern sea-grass meadows or kelp forests, based on the well-preserved Early Silurian thallophytic algal meadow from Anticosti Island, eastern Canada.

Late Katian (Late Ordovician) carbonate mudmounds in the Tureso Formation, Peary Land, North Greenland, succeed normal marine faunas dominated by brachiopods, bryozoans, cephalopod and gastropod molluscs, aulaceratid stromatoporoids, corals and receptaculitid algae, in the Borglum River Formation, and are themselves succeeded by organic-rich, largely barren limestones. This peri-Laurentian succession suggests deteriorating environmental conditions from a normal marine to a more restricted basin during the Late Katian and Hirnantian, against a background of gradual marine regression following the peak of the Boda Warming Event. The generally low-energy depositional setting probably lay within the Inter-Tropical Convergence Zone on the equator.

The great ordovician biodiversification event (GOBE) is one of the major biotic revolutions in Early Paleozoic marine ecosystems. Through three internationally coordinated IGCP projects (IGCP 410, 503 and 591) in the past two decades, an enormous amount of paleontological, stratigraphical, paleoecological, and paleobiogeographical data have been accumulated, leading to a number of significant discoveries and common understandings regarding the GOBE. First, the multiple radiation pulses spanned nearly the entire Ordovician Period (more than 40 Ma), with several diversity acmes. Second, the biotic radiations were highly diachronous, characterized by different timing and rates in different regions. Third, the radiations were not associated with fundamental changes in the marine environments, but were rather controlled by both intrinsic factors (macroevolutionary regularities) and extrinsic forces (gradual environmental changes). Case studies conducted in South China have contributed greatly to the understanding of GOBE at the global scale. Future work on the GOBE includes more in-depth case studies to reveal the exact process and pattern of the radiations by combining systematic paleontology, high-resolution biostratigraphy, sedimentology, plate tectonics and geochemistry. This will help improve our understanding of the dynamics of the radiation and co-evolution between the organic and inorganic realms of Ordovician marine ecosystems.

The palaeocontinent Laurentia experienced pulses of major marine transgression during the Late Ordovician (Katian) and was covered by extensive equatorial to subtropical epicontinental seas. Brachiopods that evolved in the newly created habitats showed increasingly strong endemism from the early to late Katian. At the faunal level, the Laurentian epicontinental brachiopod (LEB) fauna became ubiquitous in the epicontinental seas, with a high level of generic homogeneity but little in common with the coeval faunas in other palaeotropically located tectonic plates. At the level of species distribution, there was limited mixing between palaeoequatorial intracratonic basins and higher tropical to subtropical pericratonic shelves within Laurentia by late Katian. This was demonstrated by the palaeogeographical distribution of several species lineages and morphological clines along latitudinal and other ecological gradients. Such a high level of endemism suggests an extreme specialization of the LEB fauna in the ...

The early Katian (Late Ordovician) was marked by a major greenhouse episode and the early stage of a first-order marine transgression that led to the flooding of much of North America during the middle–late Katian. Multivariate analyses of 33 brachiopod faunas of early Katian (Trentonian, Chatfieldian, late Caradoc) age, including 252 rhynchonelliform genera, demonstrate that the “Trentonian brachiopod faunas” of Laurentia were already clearly differentiated into a Scoto-Appalachian fauna and an epicontinental fauna. Globally, four distinct faunal clusters are identified: Kazakhstan, Avalonia, epicontinental Laurentia, and Scoto-Appalachia. The Scoto-Appalachian fauna, which originated during the Sandbian, persisted into the early Katian and became most closely related to the brachiopod faunas along the western margins of Laurentia. The early Katian epicontinental faunas of Laurentia were more closely related to the coeval brachiopods of the Lithuanian–North Estonian confacies belts of Baltica than to the Scoto-Appalachian fauna. Palaeoecological control on the faunal endemism within Laurentia was attributable to isolation of Appalachian foreland basin by faulting and peripheral bulging during the early Taconic Orogeny, palaeolatitudinal faunal gradient from the subtropical Appalachia to mid-tropical epicontinental Laurentia, as well as different water depth, water temperature, and substrate types between the two palaeogeographical settings of Laurentia.

A Darriwilian (late Middle Ordovician) brachiopod fauna from the Lower Formation of the Chiatsun Group at Jiacun, northern Nyalam, southern Tibet, consists of ten brachiopod species, forming a distinct Aporthophyla–Paralenorthis Association. Its taxonomic composition is typical of the Aporthophyla Fauna that occupied lower BA2 to upper BA3 benthic environments on sandy lime mud substrates. The occurrence of Paralenorthis in southern Tibet is confirmed for the first time, represented by P. costata sp. nov. Numerical analyses (PCA and CA) of 18 Darriwilian brachiopod faunas from ten palaeoplates or terranes indicate that: (1) the Aporthophyla Fauna was confined to a specific latitudinal belt although it had a wide lateral distribution from the large palaeocontinents of Gondwana to Laurentia; (2) the Saucrorthis Fauna, a typical late Middle Ordovician regional fauna, is limited to a much smaller area, marginal to the Gondwana supercontinent; (3) the strong provincialism persistent in the late Middle Ordovician contributed to increased gamma biodiversity during the Great Ordovician Biodiversification Event.

Multivariate analysis of 197 well-preserved specimens among 11 species of late Late Ordovician (Katian and Hirnantian) plaesiomyid brachiopods from North America revealed two trends of morphological changes: (1) increasing globosity and dorsal convexity from the early to late Katian, and (2) coarser, but fewer ribs in species from the paleoequatorial intracratonic seas compared with species from the mid- to high-tropical pericratonic shelves and platforms. Another notable change, albeit not quantified, was the enlargement of cardinal process in plaesiomyids from early to late Katian, characterized by a predominantly trilobed cardinal process in the intracratonic species versus a bilobed cardinal process in pericratonic species. Increases in dorsal convexity and shell globosity are interpreted to have allowed for development of a larger lophophore, improving the capacity and efficiency of filter feeding and gas exchange. Smaller but more frequently bifurcating ribs would have led to more numerous setae near the margin of the shell, resulting in increased sensitivity to environmental stimuli. Increased size and number of lobes of the cardinal process would have allowed for larger diductor muscles to open a larger, heavier shell. In this study, two new species, Plaesiomys periosa sp. nov. and Plaesiomys lenzi sp. nov., are proposed, and two existing species are transferred from Dinorthis to Plaesiomys.

A large and abundant columnar stromatoporoid, Quasiaulacera n. gen., from the Ellis Bay Formation, up to 3 m long and 40 cm in diameter, marks the Hirnantian (latest Ordovician) of Anticosti Island. Two species are present: Quasiaulacera stellata n. sp. from the basal Ellis Bay Formation (basal Prinsta Member, lower Hirnantian) along the northeastern coast of the island, and the type species Q. occidua n. sp. from the upper Ellis Bay Formation (Lousy Cove Member, upper Hirnantian) in the western carbonate facies of the island. Quasiaulacera is rare or absent in the reefal Laframboise Member (uppermost Hirnantian) of the formation. The new genus differs from Aulacera in the underlying Vaureal Formation (upper Katian) in having a large central axial zone marked by a single stack of large, convex-up cyst-plates, that is surrounded by a middle layer of small, concentric microcyst-plates, in places denticulate, and an outer layer composed of concentric laminae with dense pillars, in which microcyst-plates are either absent or rare. The outer two layers are defined by longitudinal fluting; there are no branching forms. Both species demonstrate a ball-like holdfast system, some with diameters of 30 to 70 cm, microbially cemented into the substrate. Quasiaulacera “gigantism” in the paleotropical Anticosti Basin evolved at a time of global cooling associated with the Hirnantian glaciation in south polar Gondwana, but terminated in mass extinction of the aulaceratids at the O/S boundary in Laurentia. This supports other evidence that the Hirnantian featured not only generic loss, but also innovation and migration in tropical latitudes.

Taxonomic identification of Paleozoic solitary rugose corals relies heavily on serial sections to determine the ontogenetic development of skeletal structures. Previously, small rugose corals have been difficult to study because their size and curvature make it difficult to serially section them at a right angle to the longitudinal growth axis. In this paper, we describe a newly designed apparatus, with a rotatable clamp to hold the fossil coral. This guarantees easy adjustment of the cutting angle so that serial sections can be made at changing angles that are always at a right angle to the curved longitudinal axis of a rugose coral. In addition, the apparatus allows the distance between consecutive sections to be controlled precisely to mm scales.

Multivariate analysis based on nine biometric characters of 171 Late Ordovician rhynchonellide specimens from nine upper Sandbian–upper Katian localities in North America supports the hypothesis that one of the diagnostic taxa of the North American epicontinental brachiopod fauna, Hiscobeccus, evolved from Rhynchotrema, which lived predominantly in peri-cratonic settings. The oldest known Hiscobeccus, H. mackenziensis of early Katian age, exhibits transitional characteristics between Rhynchotrema and Hiscobeccus, and it clusters more closely with Rhynchotrema than with younger species of Hiscobeccus of mid–late Katian (Maysvillian–Richmondian) age. Diversification of the Hiscobeccus lineage in epicontinental seas was characterized by drastic increase in shell size, globosity and lamellosity, especially in palaeoequatorially located inland basins. Such morphological trends are interpreted as adaptation to relatively shallow, muddy substrates, moderate water turbulence, relatively low oxygen content and unstable supply of nutrients in generally overheated epicontinental seas with sluggish circulation.