Llandovery sporomorphs and graptolites from the Manbo Formation,the Mojiang County,Yunnan, China

Llandovery sporomorphs and graptolites have been recovered from the Manbo Formation, Mojiang area, western Yunnan, China, which belonged to the Indo-China Palaeoplate in the Palaeozoic. The graptolite fauna, including 8 genera and 12 species, is considered Mid Telychian, Llandovery in geological age, confirming the existence of Llandovery rocks in this region. The Silurian stratigraphical sequence of this area is reconsidered as in the ascending order: Manbo Formation (Llandovery–early Wenlock), Shuiqing Formation (late Wenlock–Ludlow) and unnamed formation (Pridoli?). The sporomorph assemblage from the Manbo Formation includes seven species in five genera. The dominant members of this assemblage are Tetrahedraletes medinensis and Laevolancis chibrikovae. Based on the low diversity and low abundance, the geological age of this assemblage is considered to be approximately the Telychian, Llandovery. The parent plants of sporomorphs probably inhabited the landmass near Mojiang area, these sporomorph-producing plants probably included bryophyte-like land plants and primitive vascular land plants. The sporomorph evidence shows that the South China and Indo-China palaeoplates may have been in close proximity (maybe with some continental bridges linking them) to each other at least in the Llandovery. They were also closely related with Gondwanaland in the Llandovery.     

A Middle Llandovery shelly fauna from Motala in Östergötland,south central Sweden. 1.Trilobita

A temporary exposure of Middle Llandovery (Aeronian) shales in the Swedish town of Motala has yielded a rich collection of shelly fauna and graptolites. The shelly fauna is restricted to a thin mudstone band in a graptolitic shale sequence, and is within theconvolutus Biozone. This mudstone band may be correlated with a similar mudstone in the Kolka core from northwestern Latvia. The faunas, including the trilobites, from the two occurrences represent the same species. In the collection from Motala, nine species of trilobites are present, of whichAcernaspis dispersa sp. nov. is new. The material represents the first trilobite fauna described from the Middle Llandovery of Sweden.     

Aeronian (Llandovery, Lower Silurian) palynomorphs and graptolites from the Lipeón Formation, Eastern Cordillera, north-west Argentina

The lower levels of the Lipeón Formation, in the Eastern Cordillera, north-west Argentina, yield a marine-dominated palynomorph assemblage, together with graptolites of mid to late mid Llandovery age (Demirastrites convolutus and probably Stimulograptus sedgwickii zones). The palynomorph assemblage is dominated by acritarchs, but also contains algae and terrestrial cryptospores. Crassiangulina variacornuta, considered a potentially good global biostratigraphical marker for the Upper Llandovery is recovered for the first time from the Silurian of Argentina. The occurrence of this species in strata not younger than late Aeronian, and independently dated by graptolites, indicates an early first appearance for Crassiangulina variacornuta, in the Lipeón Formation, below the Aeronian/Telychian boundary. The lower part of the unit corresponds to a quiet marine environment; thus supporting that Crassiangulina variacornuta is a facies-sensitive acritarch.     

Early Silurian (Rhuddanian) rugose corals and sponges from the Ak-Kerme Peninsula,Kazakhstan

An assemblage of earliest Silurian (Llandovery, Rhuddanian) fossils from South Kazakhstan (Ak-Kerme Peninsula, Lake Balkhash) contains solitary rugose corals (Calostylis denticulata, Streptelasma? sp., and Cystipaliphyllum sp.) and the demosponge Calycocoelia typicalis, which are described here. This assemblage occurs with previously described brachiopods and constitutes a post extinction survival fauna; such faunas are poorly known and this study fills a gap in our knowledge. All three genera of Rugosa were transitional across the Ordovician–Silurian boundary and are also reported from other parts of Kazakhstan, Uzbekistan, and Tajikistan during the Llandovery. Streptelasma had already been present in Kazakhstan during the Ordovician, while during the Rhuddanian Calostylis immigrated from Baltica or China, and Cystipaliphyllum from the Australian part of Gondwana. Demosponges are rare during the Llandovery but probably had a cosmopolitan distribution. Calycocoelia typicalis marks the first Rhuddanian record of lithistid demosponges, and the first record of Silurian demosponges from Kazakhstan.     

Evaluation of the Salinic I tectonic, Cancañiri glacial and Ireviken biotic events: Biochemostratigraphy of the Lower Siluriansuccession in the Niagara Gorge area, Canada and U.S.A.

Well-preserved brachiopods from the Niagara Gorge area, Anticosti Island, Britain, Gotland and Estonia were utilised to delineate a complex isotopic evolution for Llandovery-Wenlock seawater. The Sr-isotope record reflects the Salinic I tectophase of the Late Llandovery in the continuous increase in ⁸⁷Sr/⁸⁶Sr values from 0.708070 to 0.708346. The Salinic II tectophase is marked by relative constancy of Sr isotope values until the Late Wenlock when it rises from 0.708345 to 0.708430. The second tectonic phase was therefore likely only of a regional nature. The carbon isotopes during the Llandovery fall within a band of about − 1‰ to + 3‰, a range comparable to modern low-latitude brachiopods. A large positive δ¹³C excursion of about 3‰, identifies the Ireviken event/excursion, characterizes the Early Wenlock. The biotic crisis and the isotope excursion itself may be ultimately related to the onset and duration of the Cancañiri glaciation, although a direct causative scenario is as yet unknown. The oxygen isotopic trends of well-preserved brachiopods clearly reflect a warm climate interval during the latest Llandovery associated with the Silurian sea level highstand. Subsequently, in the Early Wenlock, the sea level fell with the onset of the Cancañiri glaciation in the southern hemisphere. This is reflected in a significant positive δ¹⁸O excursion, particularly in brachiopods from the Niagara Gorge area. Brachiopods from lower latitudes were awash in warm tropical currents and therefore exhibit somewhat more negative δ¹⁸O values, indicating a lesser cooling gradient.     

Chinese origin and radiation of the Palaeozoic crinoid family Petalocrinidae

The Ordovician to Devonian family Petalocrinidae includes 28 species belonging to 5 genera. This family is unique because the arm plates are fused into a large fan or cylinder. Paleobiogeographic occurrences of this family include Laurentia, Baltica, Avalonia, South China, Sibumasu, and Perunica blocks. The family has the oldest petalocrinids from China. An early radiation of this clade resulted in three genera during the Llandovery of China. Petalocrinus became cosmopolitan during the Llandovery and Wenlock, and the youngest genus is present in the Lower Devonian of the Czech Republic. Taxonomic determination for the Petalocrinidae is based on the fused arm plates instead of cup plates. The diverse morphology of these arm plates suggests a variety of aerosol suspension-feeding modes may have been used by petalocrinids.     

Age of the Silurian Wuxiahe Formation in Langao,Northwest China: New conodont data

A recent study of conodonts from the Wuxiahe Formation (lower to middle part) in the Ziyang-Langao region suggested its age of middle Telychian (Llandovery) to lower Sheinwoodian (Wenlock), contradicted by subsequent graptolite studies indicating an age of late Telychian for the same interval. New samples from the Qiaoxi section for conodonts to re-access the age of the Wuxiahe Formation collected in this study show that the lower to middle part of the formation belongs to the Pterospathodus amorphognathoides amorphognathoides Biozone, suggesting the age of late Telychian; thus, the Llandovery–Wenlock boundary in the section is most probably higher than previously estimated, but its precise position is not determined since the identification of the Wenlock graptolite Cyrtograptus cf. lundgreni in the section is to be further confirmed. Based on the conodont faunas recognized in the Qiaoxi and Tianwancun sections, the base of the Wuxiahe Formation in the Ziyang-Langao region is diachronous, i.e., not higher than the upper Telychian Pterospathodus amorphognathoides amorphognathoides Biozone at Qiaoxi, but not lower than the lower Sheinwoodian Kockelella ranuliformis Biozone at the Tianwancun setion.     

Strophomenidae,Leptostrophiidae, Strophodontidae and Shaleriidae (Brachiopoda,Strophomenida) from the Silurian of Gotland,Sweden

Twelve species of Brachiopods are described from the Silurian of Gotland, six furcitellinines and six “strophodontids.” One is new—Strophodonta hoburgensis n. sp. The furcitellinines are moderately common and diverse in the lower part of the succession, but the last species disappears in the middle Hemse beds (~middle Ludlow). Three genera are represented: Bellimurina, Pentlandina and Katastrophomena, with the species and subspecies B. wisgoriensis, P. tartana, P. loveni, P. lewisii lewisii, K. penkillensis and K. antiquata scabrosa. Most of the taxa are confined to low energy environments, but P. loveni was evidently specialized for the high energy reef environments of the Högklint Formation. B. wisgoriensis displays environmentally induced morphological variability in developing strong, frilly growth lamellae in high-energy environments. The “strophodontids,” although belonging to three different families, share a common morphology consisting of denticles along the hinge line, a semi-circular outline, unequally to finely costellate ornament and, most importantly, a concavo-convex profile with both valves of the same curvature, enclosing a very small body chamber. Two leptostrophiids are generalists, occurring in both high- and low-energy environments and with long stratigraphical ranges [Mesoleptostrophia filosa; latest Llandovery through the entire Ludlow. Brachyprion (Brachyprion) semiglobosa; latest Llandovery to latest Wenlock]. The third leptostrophiid (Brachyprion (Erinostrophia) walmstedti) is short ranged and occurs in low-energy environments in the latest Llandovery. The species belonging to the Strophodontidae (Strophodonta hoburgensis n. sp.) and Shaleriidae [Shaleria (Janiomya) ornatella and S. (Shaleriella) ezerensis] occur only in high-energy environments and have a short range within the late Ludlow.     

Proetid trilobites from the middle Telychian (Llandovery,Silurian) Ningqiang Formation,Shaanxi, China

Four proetid trilobite species, Chuanqianoproetus guizhouensis Yin in Yin and Li, 1978, C. shuangheensis Wu, 1977, C. sp., and Latiproetus guizhouensis Yin in Yin and Li, 1978, are described from the Ningqiang Formation in Ningqiang County, Shaanxi, China. They are middle Telychian (Llandovery, Silurian) in age. Chuanqianoproetus and Latiproetus are both regarded as members of the subfamily Warburgellinae; the former has been considered to be a junior subjective synonym of Astroproetus, but on the basis of its morphology we argue here that they represent two independent genera. The poorly sorted bioclastic grainstones containing trilobite sclerites may indicate their deposition in turbulent conditions on an open marine platform.     

Peridermal (cortical) ultrastructure indictyonema cf.rhinanthiforme bulman,and the significance of its bithecae

The cortical ultrastructure ofDictyonema cf.rhinanthiforme Bulman, from the early Llandovery of Cornwallis Island, is shown to consist of cortical bandages of the same basic kind as those seen in many graptoloids (e.g. Crowther & Rickards 1977, Crowther 1981) and confirms the predictions of Andres 1977, and Crowther & Rickards (op. cit.) with respect to the presence of such bandages in dendroids.D. cf.rhinanthiforme still occurred some 60 Ma after the type specimens of the species and is significant in two further respects: in confirming the evolutionary conservativeness of dendroids and in enabling Bulman’s (1933) morphological series of bithecal types to be interpreted as a broad evolutionary sequence in which bithecae with simple tubes gradually change to those with rather complex apertural regions.     

Les assemblages de graptolites du llandovery dans le synclinorium du Ménes-Bélair (Massif Armoricain)

Ampelites in the lower member of the Formation 0839 de la Lande-Murée (Silurian of the Ménez-Bélair Syncline) have yielded rich and well-preserved graptolite faunas. This material, and that in older collections, indicates the presence of all or part of the Turriculatus, Crispus and Griestoniensis Zones. Earlier Llandovery graptolite zones are not represented in the Ménez-Bélair Syncline and breaks encompassing the Lower Llandovery and the earliest part of the Upper Llandovery is envisaged.     

A late Rhuddanian (early Llandovery,Silurian) trilobite association from South China and its implications

A recovery trilobite association after the end-Ordovician mass extinction, the ‘Encrinuroides’ Association, is documented from the lower Niuchang Formation (upper Rhuddanian, lower Llandovery, Silurian) of Gaojiang, Meitan, northern Guizhou, South China paleoplate, including 10 genera of eight families. Three subassociations of this association could be differentiated, i.e., ascendingly the ‘Encrinuroides’-Eoleonaspis Subassociation, the ‘Encrinuroides’-Aulacopleura (Paraaulacopleura) Subassociation, and the ‘Encrinuroides’-Meitanillaenus Subassociation. The succession of these subassociations in the section indicates a shallowing upward trend of the environment as a result of regional tectonic activities (i.e., the Qianzhong Uplift) against the background of the Rhuddanian global transgression. A relatively complete trilobite succession in South China across the Ordovician–Silurian transition has been summarized and its implications for the trilobite macroevolution of this particular time interval are discussed in detail.     

Le Silurien et le Dévonien basal dans le Nord de la province de Seville (Espagne)

In the studied area, on the southern slope(«Ossa-Morena Zone) of the Sierra Morena (Spain) the Silurian and earliest Devonian (Lochkovian = approximately Gedinnian) consist of about 130 m of black, argillaceous, largely euxinic graptolitic slates, which, by the intermezzo of the dark «Limestones with Orthoceras and Scyphocrinus (late Ludlow and Pridolian), are divided into two inequal units, namely the Lower and Upper Graptolitic Slates. The occurence of 21 Graptolite zones and horizons was established, starting off with the basal Llandovery (A. acuminatus zone) and ending up with the Upper Lochkovian (M. hercynicas zone). This condensed tripartite graptolitic sequence, both lithologically and faunally, compares closely with the typical development of the Palaeotethys, as known from Thuringia, Carnic Alps, Sardinia and Northwest Africa. Certain graptolite species and details of the graptolitic succession (for instance across the Wenlock-Ludlow junction) that were hitherto known only or essentially from Thuringia, are recognized also in southern Spain.     

Revised conodont stratigraphy of the Cellon section (Silurian,Carnic Alps)

The Cellon section, located in the Carnic Alps, is a reference section for the Silurian of the world. The conodont association of the section is revised according to the most recent taxonomy and the biostratigraphy updated in the basis of the recently published zonation schemes. Seventy taxa (species and sub‐species) belonging to 23 genera have been identified, allowing the discrimination of 15 biozones from the upper Llandovery to the end of the P?ídolí . However, some of the uppermost Llandovery and Wenlock biozones, corresponding to black shale intervals, have not been documented.     

扬子区中、晚奥陶世和兰多维利世四射珊瑚起源、扩散及生物古地理关系

扬子区中奥陶世—志留纪兰多维利世四射珊瑚产出丰富 ,尤以兰多维利世最为繁盛。目前已报道的1 2 3属 (包括中奥陶世 4属 ,晚奥陶世 2 5属 ,兰多维利世 94属 )中 ,有 30属最早出现在扬子区 ,尔后扩散到欧洲、北美和其它邻区。例如 :Calostylis最早出现在川南的中奥陶世 (Llandeilo)地层中 ;Aphyllum和Cantrillia最早出现在浙西的晚奥陶世中Ashgill地层 ;扭心珊瑚类Briantelasma ,Pycnactis和Tunguselasma等 ,最早出现在黔东北晚Ruddanian地层 ;柱珊瑚类Ceriaster、Stauria、Amplexoides、Synamplexoides等 ,泡沫珊湖类Maikottia ,Rhizophyl lum等均最早出现在黔东北的中兰多维利统 (MiddleLlandovery)。根据这些资料 ,我们认为扬子区应该是奥陶纪和志留纪四射珊瑚起源中心之一。文中论述扬子区中奥陶世—兰多维利世四射珊瑚动物群特征及其生物古地理关系。该区中奥陶世珊瑚以穿孔珊瑚类的Calostylis和Yohophyllum为特征。下扬子区浙西晚奥陶世三衢山组 (中Ashgill)四射珊瑚群有某些澳大利亚分子Hillophyllum和Bowanophyllum ;而上扬子区晚Ashgill观音桥层的四射珊瑚动物群与北欧同期珊瑚群有高度的相似性。这表明扬子区当时与欧洲具有较密切的古生物地理关系。扬子区兰多维利世四射珊瑚群与西伯利亚。     

A Lower Silurian (Aeronian) radiolarian assemblage from black cherts of the Armorican Massif (France)

The Chalonnes-sur-Loire outcrop is the most complete Llandovery section in the Ligerian domain (Armorican Massif, NW France); it displays a ca. 10 m-thick sequence of organic-rich black bedded cherts alternating with black graptolitic shales, which were deposited above glaciomarine diamictites of the Hirnantian glaciation. It is likely the black cherts accumulated under eutrophic waters, on the outer shelf part (distal offshore) of a Gondwanan margin, situated at intermediate to high latitudes of the Southern hemisphere. Hydrofluoric acid processing allowed the extraction of radiolarians; seven species are identified in the best preserved sample discovered so far. All seven are common species in tropical assemblages known from Alaska and Nevada, which are characteristic of the Orbiculopylorum assemblage, of Aeronian to early Telychian age. This age is in good agreement with independent age control from graptolites in the Chalonnes section, suggestive of an Aeronian age for the radiolarian-yielding level.     

Taxonomy and palaeoecology of the mollusc Pterotheca from the Ordovician and Silurian of Scotland

A large sample of the bizarre bellerophontiform mollusc Pterotheca from the Upper Llandovery Wether Law Linn Formation in the Scottish Pentland Hills shows marked polymorphic asymmetry. A survival strategy that presents to a predator a mosaic of different search images is suggested to account for the marked variability of the Pterotheca morphology. Multivariate comparisons with Pterotheca mullochensis from the Llandovery of Girvan, P. simplex from the Caradoc of Girvan, P. cf. simplex from the Caradoc of the Northern Belt of the Southern Uplands and P. aff. mullochensis from the Llandovery in the Pentland Hills have helped clarify the morphological differences between these groups. A new species, Pterotheca trimerelloides , is established for the specimens from the Pterotheca beds in the Wether Law Linn Formation. □ Mollusca, Silurian, Ordovician , Pterotheca, taxonomy, palaeoecology.     

Graptolite extinction at the Llandovery—Wenlock boundary

Combined graptolite range data through the late Llandovery and early Wenlock of the Canadian Arctic Islands, the British Isles, and Lithuania reveal that survivorship rates from one zone to the next are between 56 and 85%, except at the Llandovery—Wenlock boundary, where only 19% (8 of 42) of the taxa of the upper sakmaricus—crenulata Zone survive into the centrifugus Zone. The high rate of graptolite extinction appears to coincide with glacioeustatic sea-level fall and may be attributed to changing oceanic temperatures, salinity, circulation patterns, oxygenation, and/or productivity associated with the onset of a glacial maximum event. □ Graptolite, extinction, Silurian, Llandovery, Wenlock.     

Dissepiments in the graptolite Monograptus turriculatus

An example of the graptolite Monograptus turriculatus (Barrande, 1850) from the crispus Biozone (Silurian, Llandovery) of the Girvan district, Scotland, shows the first recorded instance of dissepiment formation in graptoloid graptolites. The dissepiments are formed by the fusion of thecal spines with the dorsal wall of the adjacent part of the succeeding whorl of this spiral graptolite. The formation of these structures appears easiest to envisage using models of the graptolite colony that do not involve extrathecal tissue. □ Graptolithina , Monograptus, morphology, functional morphology, Silurian, Llandovery.     

A NEW SILURIAN EURYPTERID (ARTHROPODA: CHELICERATA) FROM CHINA

Abstract:  The oldest eurypterid from China is described as Hughmilleria wangi sp. nov., from the Xiaoxiyu Formation (Silurian: latest Llandovery) of Hunan Province. H. wangi is relatively similar to two species from North America, but differs in the development of epimera on the postabdomen, a slightly wider carapace, a styliform telson and the dimensions of the penultimate podomere of the paddle. The Llandovery age of the specimen substantially reduces the ghost range of the genus Hughmilleria . The exact phylogenetic relationship between the different species in Hughmilleria , the most basal genus in the pterygotoid clade, cannot be resolved because the plesiomorphic states within this clade are poorly known. The shapes of the telson and swimming paddle of the Chinese species suggest that it is more primitive than its North American relatives, which is in accord with its greater age.