New data on the exoskeleton of the osteostracan genus Aestiaspis (Agnatha) from the Silurian of Saaremaa Island (Estonia) and the Severnaya Zemlya Archipelago (Russia)

The histological structure of exoskeleton of the osteostracan genus Aestiaspis Janvier et Lelievre, 1994 from the Silurian of Saaremaa Island is examined for the first time. The preservation of the material enables the fine exoskeleton structure to be described in detail. The study of Aestiaspis from Saaremaa Island and the Severnaya Zemlya Archipelago has shown structural details of exoskeleton sculpture. The formation of consolidated cephalothoracic shield in the phylogeny of Tremataspidoidei is discussed. The taxonomic position of the genus Aestiaspis in the Osteostraci system is analyzed.     

Aspects of recent advances in the Ordovician stratigraphy and palaeontology of China

The continuous and richly fossiliferous Ordovician succession of China (particularly South China) comprises a heterogeneous suite of litho- and bio-facies, which has been a main focus of stratigraphical and palaeontological research in recent years. Among the seven GSSPs established in China, three are within the Ordovician System, and the GSSP of the Darriwilian Stage at Huangnitang, Changshan County, western Zhejiang Province, was the first “golden spike” in China and the first for the Ordovician System. A series of case studies have revealed that: (1) the Ordovician radiation of some fossil groups on the Upper Yangtze Platform (e.g., brachiopods and graptolites) reached their first α-diversity acme in the Didymograptellus eobifidus Biozone, four zones earlier than the global trend; (2) the β-diversity peak was attained 3–4 zones later than the α-diversity peak; (3) many brachiopod communities or faunas first occurred in the central part of the Upper Yangtze Platform and subsequently expanded to both more offshore and near-shore facies; (4) diachroneity existed in many aspects of the radiation. The end-Ordovician mass extinction was a severe event in South China. Two pulses of the extinction are recognized for a number of major fossil groups, some being most strongly affected during the first pulse whereas the others suffered during the second pulse. Macroevolution during the Ordovician–Silurian transition has been investigated in detail, and the role of the Lazarus effect has been found to be less important than previously believed.     

Symbiosis of cornulitids with the cystoporate bryozoan Fistulipora in the Pridoli of Saaremaa,Estonia

Cornulites sp. and Fistulipora przhidolensis formed a symbiotic association in the Pridoli (latest Silurian) of Saaremaa Island, Estonia. This Cornulites sp.–F. przhidolensis association is the youngest example of cornulitid–bryozoan symbiosis. Symbiosis is indicated by intergrowth of both organisms. The cornulitids are completely embedded within the cystoporate bryozoan colony, leaving only their apertures free on the growth surface of bryozoan. In terms of food competition, this association could have been slightly harmful to F. przhidolensis as Cornulites sp. may have been a kleptoparasite. There may have been a small escalation in the evolution of the endobiotic life mode of cornulitids as the number of such associations increased from the Ordovician to Silurian. It is likely that Palaeozoic bryozoan symbiosis reached its maximum in the Late Ordovician. Most of the symbiotic bryozoans in the Palaeozoic are trepostomes, and the diversity of symbiotic associations was also greatest among trepostomes.     

The earliest vascular land plants: continuing the search for proof

New collections from Bringewoodian strata (Silurian, Ludlow Series, Saetograptus leintwardinensis incipiens Zone) in Wales have yielded the oldest known specimens of the plant Cooksonia . From evidence at younger (Eř;éolí/Downton) horizons this genus is considered to be a vascular plant; although no tracheids have been isolated from the Bringewoodian specimens, on the basis of comparative morphology they are concluded to be the oldest recorded tracheophytes. The types of evidence relevant to the identification of vascular plants are briefly reviewed, and the relationships of the Welsh Cooksonia flora to other late Silurian floras are discussed. Confident stratigraphical dating is a prerequisite for any discussion of early plant evolution, emphasising the desirability of an integrated approach incorporating both geologial and palaeobotanical investigations. The dating of two published records of diverse Silurian floras, including lycopods, is questioned; recent dating of the Australian Baragwanathia flora as early Ludlow on the basis of graptolites is not supported by the shelly faunal evidence, which indicates a correlation within the Lower Devonian.     

Occurrence of Giant Borings of Osprioneides kampto in the Lower Silurian (Sheinwoodian) Stromatoporoids of Saaremaa,Estonia

The distribution of Osprioneides is more environmentally limited than that of Trypanites in the Silurian of Baltica. Osprioneides probably occurred only in large hard substrates of relatively deepwater muddy bottom open shelf environments. Osprioneides were relatively rare, occurring in 4.7% of all stromatoporoid specimens in that environment, in contrast to small Trypanites-Palaeosabella borings, which occur in 88.4% of stromatoporoids and 88.9% of heliolitid corals. Osprioneides is reported only from the lower Sheinwoodian stromatoporoids of the exposed Silurian of Saaremaa (Wenlock to Pridoli). Osprioneides borings probably played a minor role in the general bioerosion in the Silurian of Baltica.     

The Palaeobiogeography Of Silurian Ramphoprionid Polychaete Annelids

Silurian palaeobiogeography of the Ramphoprionidae (Annelida; Polychaeta) is outlined. Members of the family are reported from northern Europe (Estonia, Sweden and England), the Russian Arctic (Severnaya Zemlya), and the Canadian Arctic (Baillie–Hamilton Island). These areas were located fairly close to the palaeoequator during the Silurian and a faunal exchange is indicated by the broad, intercontinental distribution of the family. A few taxa may, however, have been endemic. Ramphoprionids had long stratigraphical ranges and were generally fairly rare during the Silurian, infrequently exceeding ten per cent of the jawed polychaete faunas.     

Anatomy and phylogenetic significance of Eoconularia loculata, a conulariid from the Silurian of Gotland

The type material of Eoconularia loculata (Wiman, 1895), a conulariid with high, bifurcated septa, was originally found in an erratic boulder, hence the source-rock is as yet unidentified. Recently, a rich material of the species has been discovered at eleven localities in the Silurian Hemse Beds of Gotland Another two localities in the Slite Beds (Wenlockan, Sheinwoodian) revealed what is assumed to be the ancestor of E loculata. This ancestral form probably constitutes a separate taxon distinguished from E. loculata in having simple, unbranched septa. E. loculata is re-described, and four ontogenetic stages in septal development are recognized. During stage 1, the most juvenile stage, the septa are simple. The septa in stages 3 and 4, the adult stages, are coarse and bifurcated. The affinities of conulariids are discussed, with the conclusion that the group shares a number of similarities with modem scyphomans. The microstructures of the exoskeleton show several similarities with coronatids, and the septa are interpreted to be homologous with the internal structures of stauromedusids. The stratigraphical distribution of all currently known septate conulariids suggests that septa were a primitive morphologic feature ranging from early? Ordovician to late Silurian. The simplest type, however, persisted at least into the early Permian. Five of the eleven described septa types have been found only among the conulariids from Gotland. □Conulariida, EOCONULARIA LOCULATA, bifurcated septa, taxonomy, ecology, morphology, Scyphozoa, Sweden, Gotland, Silurian.     

A conodont, thelodont and acanthodian fauna from the Lower Přídolí (Silurian) of the Much Wenlock area, Shropshire

Conodonts, thelodonts and acanthodians have previously been collected from the P?ídolí of Shropshire (Welsh Borderland) from bone beds such as the Ludlow Bone Bed. In general, specimens collected from these types of deposit are very abraded and make taxonomic studies difficult. This contribution describes well preserved thelodont microelements from two samples from the Downton Castle Sandstone Formation (P?ídolí, Silurian) of the Much Wenlock area of Shropshire. Head scales, a wide variety of transitional scales, and pore scales of the lateral line sensory canals of the thelodont Paralogania ludlowiensis (Gross) are described for the first time. A new acanthodian Nostolepis linleyensis sp. nov. and elements from the apparatus of the conodont Ozarkodina?hemensis sp. nov. are documented from the same samples. The thelodonts in both samples are typical of upper Ludlow–P?ídolí faunas from across the Welsh Borderland, and are also present in smaller numbers in the Ludlow Series of Gotland, Sweden, Saaremaa Island, Estonia, and in Latvia and Lithuania. The conodont O? hemensis sp. nov. is restricted to the Much Wenlock area of Shropshire. The co-occurrence of well preserved elements of conodonts and thelodonts suggests that they were deposited fairly rapidly with little or no re-working and that a restricted marine environment prevailed in the early P?ídolí in the Much Wenlock area of Shropshire.     

Seawater strontium isotope curve at the Silurian/Devonian boundary: a study of the global Silurian/Devonian boundary stratotype

Present application of ⁸⁷Sr/⁸⁶Sr chemostratigraphy to detailed stratigraphical tasks is limited by inaccurate calibration of the general seawater strontium curve to absolute as well as to relative time scales. For this reason, refinement of the general seawater strontium curve has been suggested, using mainly clearly defined global boundary stratotype sections. This study reports the first ⁸⁷Sr/⁸⁶Sr data from the global Silurian/Devonian boundary stratotype section and fills an existing 1-Ma gap in available data. Generally, the data from the stratotype fit the range interpolated from published ⁸⁷Sr/⁸⁶Sr data of the general curve, but the slight differences may suggest an existence of a high-order oscillation near the Silurian/Devonian boundary. Higher ⁸⁷Sr/⁸⁶Sr values in the Devonian part of boundary bed 20 (20-beta) may indicate an exotic material influx of recycled sediment.     

Upper Katian (Upper Ordovician) trans-Atlantic δ13C chemostratigraphy: the geochronological equivalence of the ELKHORN and PAROVEJA excursions and its implications

Since 2010 when the North American ELKHORN and Baltoscandic PAROVEJA isotope excursions were first described and named, their mutual age relations have remained uncertain, if not controversial. This was at least partly due to the incompleteness of the ELKHORN excursion in its reference section in western Ohio. The unexpected discovery of an apparently complete ELKHORN excursion in a drill core from St Marys in western Ohio has led to the conclusion that in terms of stratigraphical position and δ¹³C curve correspondence, the ELKHORN and PAROVEJA excursions are so similar that they apparently represent the same isotopic curve perturbation. The ELKHORN/PAROVEJA excursion occurs in the D. pacificus Graptolite Zone and uppermost A. ordovicicus Conodont Zone in the uppermost Katian Stage (Stage Slice Ka4 of Bergström et al. Lethaia 42, 97–197, 2009). Because the designation PAROVEJA was published two months before that of ELKHORN, it has priority as excursion designation. This excursion is particularly well represented in the carbonate successions in the Great Basin of western United States. Chemostratigraphy and biostratigraphy in that region show that the Richmondian transgression was contemporaneous with the beginning of the middle Katian WHITEWATER/MOE excursion. The onset of the Richmondian transgression has long been controversial but now available evidence suggests that it is of essentially the same age across large regions of the southern, western and central United States.     

A high-precision global biostratigraphy of myodocope ostracods for the Silurian upper Wenlock Series and Ludlow Series

The wide, trans-oceanic geographical distribution of myodocope ostracods during the Silurian (especially during the Ludlow and Pridoli epochs), and their widespread preservation in rocks of that age, permits the establishment of a transcontinental biostratigraphy of comparable resolution to coeval graptolite/chitinozoan/conodont biozones. Seven myodocope biozones, extending from the Homerian Stage, upper Wenlock Series Cyrtograptus lundgreni graptolite biozone to the middle part of the Ludfordian Stage of the Ludlow Series, enable a time-resolution for each biozone of circa 1 million years. These biozones can provide high-resolution correlation across Europe into Arctic Russia and Central Asia. There is also the potential for a myodocope biostratigraphy applicable from the uppermost Silurian (Pridoli) to the Carboniferous.     

NOTES ON THE APPLICATION OF THE FLUORINEDATING METHOD TO THE DATING OF SOME FOSSIL HUMAN REMAINS OF CHINA

Several new finds of fossilized human remains have been made in Chinaduring the last few years.As most of the materials were incidentally discover-ed and collected by amateur collectors,the stratigraphical position of thefossils and their relation with the associating vertebrate fossils were mostlyunknown or doubtful.     

EVOLUTIONARY ORIGIN OF A PARTHENOFORM,THE AMAZON MOLLY POECILIA FORMOSA,ON THE BASIS OF A MOLECULAR GENEALOGY

The appearance of vertebrate species that reproduce without genetic recombination has been explained by their origin from a rare hybridization event between members of two distantly related species. For the first recognized vertebrate unisexual, the Amazon molly Poecilia formosa, mostly morphological and biochemical genetic information has been available so far with respect to its evolutionary origin. DNA sequence analyses of transcribed portions of the genome (tyrosine kinase proto-oncogenes) demonstrated its hybrid state unequivocally. Both alleles can be traced in a DNA sequence-based phylogenetic tree to extant species that represent the parental species or that are closely related to the corresponding extinct forms, namely P. mexicana limantouri and a so far taxonomically ill-defined north Mexican subspecies of the P. latipinna/P. velifera complex. A rough estimate from the mutation rates dates the hybridization event further back than would have been predicted on the basis of “Muller's ratchet” for an ecologically successful species.     

Patterns of sclerobiont colonization on the rugose coral Schlotheimophyllum patellatum (Schlotheim, 1820) from the Silurian of Gotland,Sweden

Analysis of mushroom-shaped rugose corals Schlotheimophyllum patellatum (Schlotheim, 1820) from the Silurian (Upper Visby Beds, Lower Wenlock, Sheinwoodian) of Gotland, Sweden, showed that they were colonized on both the upper (exposed) and lower (cryptic) sides by a variety of encrusting and boring (sclerobiont) biotas, represented by 10 taxa and at least 23 species. Bryozoans and microconchid tubeworms, the most abundant encrusters, dominated on the cryptic undersides of the corals, while the dominant endobionts responsible for Trypanites borings overwhelmingly dominated the exposed surfaces. Except for cnidarian sphenothallids, which were exclusive colonizers of the underside of only one coral host, no other encrusters could be referred to as obligate cryptobionts. Because the upper surface of these corals was likely covered by soft-tissues during life, in specimens lifted off the sea-floor sclerobionts must have settled on the cryptic sides first. They could colonize the upper side only after the coral’s death, unless it was covered by sediment as could be the case in some flat specimens. With time, the space on the underside of the coral skeleton may have progressively been filled by sediment as well, precluding further colonization by sclerobionts. In that respect, the colonization patterns of these corals by encrusters and borers were controlled by the complex interplay of environmental factors, sclerobiont dynamics and coral growth in a given Silurian habitat. Compared with Silurian stromatoporoid hosts, the sclerobiont diversity and abundance noted on the Schlotheimophyllum corals may be regarded as representative for the Silurian as a whole.     

A proposed new global stratotype for Aeronian Stage of the Silurian System: Hlásná Třebaň section,Czech Republic

The current Global Stratotype Section and Point (GSSP ) for the Aeronian Stage (Llandovery Series, Silurian System), on Trefawr track in the Llandovery area of Wales, is an inadequate marker for precise, global, correlation. The International Subcommission on Silurian Stratigraphy has, therefore, undertaken the selection of a new GSSP for this level. The lowest occurrence of the graptolite Demirastrites triangulatus , 1.38 m above the base of the black‐shale succession of the ?elkovice Formation at the Hlásná T?ebaň section in Central Bohemia, is proposed to mark the base of the Aeronian Stage. The section, which fulfils all formal requirements for stratotype of a chronostratigraphical unit, should be considered as a candidate for the new GSSP . An abundant, well‐preserved, diverse graptolite fauna occurs through the section along with common chitinozoans, which indicate that the Spinachitina maennili Biozone spans the boundary interval. The section comprises the lower–middle Aeronian (D. triangulatus–Lituigraptus convolutus graptolite biozones) along with underlying Rhuddanian (Akidograptus ascensus–Coronograptus cyphus biozones) and Hirnantian strata. Several graptolite genera of primary importance in global correlation (Demirastrites , Petalolithus , Rastrites and Campograptus ) first appear in the lower part of the triangulatus Biozone. The structurally simple section is somewhat condensed, but there is a uniform succession of black shale without any evidence of disconformity in the broad boundary interval. The C_org isotope record exhibits a minor positive excursion just above the base of the triangulatus Biozone, whereas TOC and N isotope and elemental geochemical records provide evidence for uninterrupted sedimentation under stable, anoxic conditions.     

Revised correlation of Silurian Provincial Series of North America with global and regional chronostratigraphic units and δ13Ccarb chemostratigraphy

Cramer, B.D., Brett, C.E., Melchin, M.J., Männik, P., Kleffner, M.A., McLaughlin, P.I., Loydell, D.K., Munnecke, A., Jeppsson, L., Corradini, C., Brunton, F.R. & Saltzman, M.R. 2011: Revised correlation of Silurian Provincial Series of North America with global and regional chronostratigraphic units and δ¹³C_carb chemostratigraphy. Lethaia, Vol. 44, pp. 185–202. Recent revisions to the biostratigraphic and chronostratigraphic assignment of strata from the type area of the Niagaran Provincial Series (a regional chronostratigraphic unit) have demonstrated the need to revise the chronostratigraphic correlation of the Silurian System of North America. Recently, the working group to restudy the base of the Wenlock Series has developed an extremely high‐resolution global chronostratigraphy for the Telychian and Sheinwoodian stages by integrating graptolite and conodont biostratigraphy with carbonate carbon isotope (δ¹³C_carb) chemostratigraphy. This improved global chronostratigraphy has required such significant chronostratigraphic revisions to the North American succession that much of the Silurian System in North America is currently in a state of flux and needs further refinement. This report serves as an update of the progress on recalibrating the global chronostratigraphic correlation of North American Provincial Series and Stage boundaries in their type area. The revised North American classification is correlated with global series and stages as well as regional classifications used in the United Kingdom, the East Baltic, Australia, China, the Barrandian, and Altaj. Twenty‐four potential stage slices, based primarily on graptolite and conodont zones and correlated to the global series and stages, are illustrated alongside a new composite δ¹³C_carb curve for the Silurian. Conodont, graptolite, isotope, New York, Ontario, series, Silurian, stage.     

Late Ordovician and early Silurian Proetida (Trilobita) from north-western and central Europe

Species belonging to genera of three families of the Proetida (Proetidae, Rorringtoniidae and Toernquistiidae) are described from the upper Ashgill of southern Sweden, and the same or related species noted from the adjacent parts of northern and central Europe. Proetidae are represented by Paraproetus brevifrons (Angelin), Ogmocnemis irregularis Kielan, Ogmocnemis jaanussoni sp. nov. and Parvigena putealis sp. nov.; it is argued that all belong to the Cornuproetinae, not Tropidocoryphinae where they were previously classified. Ogmocnemis is resurrected for some Upper Ordovician species included previously in Decoroproetus . The rorringtoniid genera Rorringtonia and Madygenia are recognised for the first time in southern Sweden, and it is argued that these are probably closely related, and both are included in the same family; both are recorded for the first time from Silurian (Llandovery) strata. Zetaproetus is claimed to be a junior subjective synonym of Rorringtonia. Solariproetus , first described from north-west China, is assigned to the Toernquistiidae as a late, derived member, and S. prosthemesos sp. nov. is described from late Rawtheyan strata in the Holy Cross Mountains, Skåne and the English Lake District. Comments are given on the stratigraphical and palaeogeographical distribution of these taxa.     

The North China Steptoean positive carbon isotope excursion and its global correlation with the base of the Paibian Stage (early Furongian Series), Cambrian

The use of carbon isotope excursion in Cambrian stratigraphical correlation is a standard practice at both the intercontinental and intracontinental scales. The Steptoean positive carbon isotope excursion (SPICE) is one of the prime examples in this regard in correlating the base of the Paibian Stage and Furongian Series. A lack of definite SPICE evidence in the North China craton has been a challenge in precision correlation between North China and other palaeo‐continents. This study provides new carbonates carbon isotope data from the type locality of the Changshan Formation in Hebei Province, North China. Our new δ13C_carb data provide new objective evidence for the presence of the SPICE in North China. The sampling section is relatively condensed, and the interval of the SPICE curve is less than one and half‐metres after analysing 64 samples (the sampling interval within the SPICE is less than 10 cm). The onset of the SPICE curve in Tangshan, Hebei, occurs in the barren interval between the Neodrepanura and Chuangia trilobite zones. Based on this study and previous work, this could imply the middle part of the Prochuangia‐Paracoosia trilobite Zone in North China and can be correlated with the base of the Paibian Stage and Furongian Series.     

Ordovician and Silurian acritarch assemblages from the west Leinster and Slievenamon areas of southeast Ireland

The Lower Palaeozoic sequences west of the Leinster Granite and in the Slievenamon Inlier of southeast Ireland have been palynologically re-investigated. Most of the productive samples yielded sufficient identifiable acritarchs for positive stratigraphical age determinations for several of the formations. The samples also include rare cryptospores, scolecodonts and tubular structures. Previous work in the area west of the Leinster Granite proposed an unbroken succession from Early Ordovician Ribband Group turbidites and volcanics passing up conformably to Early Ordovician to Late Silurian Kilcullen Group. The new palynological data clearly show that the Kilcullen Group in this area is entirely Silurian (Llandovery-early Wenlock) in age, also results obtained from the same group at Slievenamon confirm the previously reported Silurian age. Ordovician acritarchs found in the Kilcullen Group of both study areas are reworked and range in age from late Tremadoc to Llanvirn. The new data reveal a major stratigraphic break between the Ribband Group dated as Early and Middle Ordovician and the Silurian Kilcullen Group. This major break extends some hundreds of kms southwest to the Dingle Peninsula and possibly equates with a similar discontinuity in the Isle of Man to the northeast. This break would thus appear to be a major feature within the northwestern Avalonian margin sequence.