滇东曲靖上志留统关底组若干腕足动物居群的生态特征

依据居群生态学的理论，采用大小－频率直方图和生存曲线，对采自滇东曲靖上志留统关底组的４种１４个腕足动物居群进行分析对比，尝试性地阐述了居群结构与沉积环境、居群形态变异与沉积环境之间的关系。     

Silurian reef-dwelling pentamerid brachiopods, Wisconsin and Illinois, USA

Eight species of pentamerid brachiopods, assigned toApopentamerus, Capelliniella, Kirkidium, Lissocoelina, Rhipidium, Supertrilobus andStenopentamerus, occur in stromatoporoid-coral reefs of the Silurian (Wenlockian) Racine Formation, Wisconsin and Illinois, USA. One new taxon,Rhipidium kuglitschi n.sp., is described. In contrast to level-bottom communities, where single pentamerid species occur in great numbers over large areas, pentamerids were generally rare members of the Racine reef fauna, and most species have localized distributions. An increase in diversity from one pentamerid species in the north to six species in the south correlates with a southward increase in reef size. Four morphologic groups of pentamerid species differed in the shape of the mantle cavity, which suggests different dynamics of suspension-feeding. Where two or more species are present in single reefs, co-occurrence of these groups represents a partitioning of the pentamerid niche. The relatively high diversity, local distributions, and morphologic distinctions among the Racine pentamerid fauna represent an evolutionary radiation and functional specialization of pentamerids in Wenlock reefs.     

The first report of epipunctae in non-plaesiomyid brachiopods from the lowest Silurian of southeastern China

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.     

Diversity,speciation, endemism and extinction in Devonian reef and level-bottom communities,eastern North America

Lower Devonian late Emsian (Bois Blanc and Clear Creek Limestones; Schoharie Formation) level-bottom communities in New York, Michigan and Illinois were moderately cosmopolitan and diverse and dominated by brachiopods and solitary rugose corals. Subsequently (Early Eifelian?), there was an important episode of cratonal patch reef building in New York (Edgecliff Member, Onondaga Limestone), southwestern Ontario (Formosa Reef Limestone, lower Detroit River Group), and the Hudson Bay Lowland (Kwataboahegan Formation) by highly diverse endemic communities. The Edgecliff reefs were built by corals whereas the Formosa and Kwataboahegan reefs were built primarily by stromatoporoids. The strong correlation between high diversity and high endemism during the reef-building episode suggests that these communities contained numberous, small species populations belonging to several major taxa — an example of rapid speciation by geographic isolation and genetic drift.     

Early Cambrian organophosphatic brachiopods from the Xinji Formation,at Shuiyu section,Shanxi Province,North China

Abundant and diverse small shelly fossils have been reported from Cambrian Series 2 in North China, but the co-occurring brachiopods are still poorly known. Herein, we describe seven genera, five species and two undetermined species of organophosphatic brachiopods including one new genus and new species from the lower Cambrian Xinji Formation at Shuiyu section, located on the southern margin of North China Platform. The brachiopod assemblage comprises one mickwitziid (stem group brachiopoda), Paramickwitzia boreussinaensis n. gen. n. sp., a paterinide, Askepasma toddense Laurie, 1986, an acrotretoid, Eohadrotreta cf. zhenbaensis Li and Holmer, 2004, a botsfordiid, Schizopholis yorkensis (Holmer and Ushatinskaya in Gravestock et al., 2001) and three linguloids, Spinobolus sp., Eodicellomus cf. elkaniiformis Holmer and Ushatinskaya in Gravestock et al., 2001 and Eoobolus sp. This brachiopod assemblage suggests a late Age 3 to early Age 4 for the Xinji Formation and reveals a remarkably strong connection with coeval faunas from East Gondwana, particularly the Hawker Group in South Australia. The high degree of similarity (even at species level) further supports a close palaeogeographic position between the North China Platform and Australian East Gondwana during the early Cambrian as indicated by small shelly fossil data.     

EARLY SILURIAN SULCIPENTAMERUS AND RELATED PENTAMERID BRACHIOPODS FROM SOUTH CHINA

Abstract:  Sixteen species from the Lower Silurian (mostly Aeronian and rarely Telychian) of South China have been assigned previously to the brachiopod family Pentameridae, mainly to the genus Pentamerus . Study of intrapopulation variation suggests that 13 species from the upper Aeronian Lojoping Formation of the Yichang area, western Hubei Province, can be synonymized with Sulcipentamerus dorsoplanus , the most abundant pentamerid species of South China but confined to the Yichang area. The conspicuously high and obtuse ventral umbo, strong ventribiconvexity and a sulcate anterior commissure warrant genus status for Sulcipentamerus , independent of Pentamerus . True Pentamerus is rare in South China, known only from upper Aeronian rocks of Guizhou Province. Multivariate analyses indicate that Aeronian pentameride brachiopods of South China are characterized by a high level of provincialism, distinct from those of Laurentia. Also, the Aeronian pentamerides of South China or Laurentia have a low degree of similarity to those of Baltica, Siberia, Avalonia, Kazakhstan and other palaeotropically located plates or terranes. Besides South China and Laurentia, the pentamerides of other palaeotropical regions constituted a relatively tight cluster. This suggests that the palaeogeographical positions of South China and Laurentia only allowed limited or periodic faunal exchange of these generally large-shelled brachiopods adapted to living in relatively shallow, warm waters.     

泥质对志留系礁滩生长的抑制作用:黔北桐梓韩家店组的例证

黔北桐梓的戴家沟剖面和狮溪剖面志留系兰多维列统特列奇阶下部的韩家店组出露完好,该组泥岩、粉砂岩中夹有厚度1—3m、直径4—7m的小型点礁。礁核相多具典型的障积格架岩特征,但生长时限短暂,群落分异度低,仅见床板珊瑚、单体四射珊瑚、苔藓虫和海百合茎,礁间为珊瑚、苔藓虫和海百合茎碎片堆积的滩相,伴生丰富的遗迹化石。在陆源碎屑快速沉积的背景下,浑浊海水频繁的富营养化过程限制了礁体纵横向生长和朝高分异度群落发展的可能性。     

Brachiopods from cryptic coral reef habitats in the northern Red Sea

In contrast to the Palaeozoic to Jurassic fossil record, modern tropical and subtropical shallow-water brachiopods are typically small-sized and mostly restricted to cryptic habitats in coral reefs, but information on microhabitat-composition is scant. At Dahab, northern Red Sea, living brachiopods of the genus Argyrotheca were only detected on massively encrusted coral colonies attached to encrusting foraminifers and coralline red algae. Three samples from autochthonous sediments underneath coral colonies are comparatively rich in the brachiopod genera Megerlia and Argyrotheca, and additionally show low numbers of Novocrania and Thecidellina. Based on a coarse-grain analysis including more than 16,000 components >1 mm, these brachiopod shells co-occur with skeletal components of 11 higher taxa. Decapods, fixosessile foraminifers, molluscs, scleractinians, and coralline red algae clearly dominate the assemblages. Brachiopods in this study always contribute less than 2% to the sediment composition. This confirms previous results that even in brachiopod habitats the contribution of brachiopod shells to the total sediment composition is almost negligible. Our study indicates that brachiopods co-occur with pteriomorph bivalves and other epifauna in the cryptic habitats with limited space for encrusters or epibionts on the undersides of scleractinians and it tentatively supports the hypothesis of brachiopods preferring habitats with low grazing pressure, because shelly components of grazers (polyplacophorans and regular echinoids) are rare in our samples.     

A new family of inarticulate brachiopods from the Lower Cambrian of northwestern Mongolia

A new genus of calcareous-shelled brachiopods, Egyngolella, with E. lenae sp. nov. selected as the type species, is described from the upper part of the Egiin Gol Formation, Atdabanian Stage, Lower Cambrian of northwestern Mongolia and is assigned to a new family that is tentatively placed in the order Obolellida. E. lenae sp. nov. is characterized by an unusual combination of features typical for different, sometimes widely divergent brachiopod lineages.     

Oldest known Dicoelosia and Epitomyonia,deep water brachiopods from the Beiguoshan Formation (Middle Katian,Upper Ordovician), Shaanxi,north China

Abstract: A diverse brachiopod fauna from a relatively deep water carbonate facies of the Upper Ordovician Beiguoshan Formation (uppermost Caradoc – lower Ashgill, middle Katian) is characterized by small shells and contains the oldest known Dicoelosia and Epitomyonia, two diagnostic taxa of deep water brachiopod palaeocommunities during the Late Ordovician and Silurian. Three new species are recognized: Dicoelosia cordiformis sp. nov., Dicoelosia perbrevis sp. nov. and Epitomyonia fui sp. nov. These pioneer forms of the family Dicoelosiidae show a relatively high degree of morphological plasticity. The shells of Dicoelosia from the Beiguoshan Formation range from the typical slender‐lobed form with a concavoconvex profile to the strongly equibiconvex, fat‐lobed morphotype that was not known previously until the late Silurian. The Beiguoshan dicoelosiids point to an important attribute of the deep water brachiopods: small generalists with high morphological plasticity, which make them ideal candidates as progenitors for the evolution of shallow water brachiopod faunas in shelf and platform depositional environments.     

Late Silurian brachiopods from Darhan Mumingan Joint Banner, Inner Mongolia

Seven brachiopod species (including three new species) and three undetermined forms are described and figured here from an unnamed stratigraphic unit which mainly consists of argillaceous and bioclastic limestone near the stratotype of the Late Silurian Xibiehe Formation of the Xibiehe section in the Darhan Mumingan Joint Banner, north of the Bateaobao area, Inner Mongolia. Three new species, Eoschizophoria minuta, Navispira navicula and Howellella asiatica are established with transverse serial sections for their interiors. All brachiopod taxa described here show that this unnamed stratigraphic unit is higher than the Late Silurian Xibiehe Formation in the Xibiehe section and is possibly transitional between the Late Silurian and the Early Devonian. Authors temporarily regard this unit as the upper part of the Xibiehe Formation in this paper.     

Paleoecologic,temporal, and spatial analysis of early Silurian Reefs of the Chicotte Formation,Anticosti Island,Quebec, Canada

Summary Reefs of the Lower Silurian Chicotte Formation are the largest and most faunally diverse known on Anticosti Island, Quebec. They reach up to 25 m in thickness and 250 m in diameter and are present predominantly at two intervals, forming a lower and upper reef cluster. Remnants of bioherms are represented on the present-day wave-cut terrace as 60 to 100 m diameter, subcircular erosional depressions known as Philip structures or as outcrop. The bioherms were relatively low structures, with approximately 3 to 5 m maximum synoptic relief, some of which developed on hardgrounds and possible paleokarst surfaces of crinoidal wackestone and packstone. Dominant skeletal framework builders and sediment producers within all of the reefs are laminar to low domical stromatoporoids, colonial cerioid and fasciculate rugose corals, colonial tabulate corals, and cryptostome bryozoans. Vertical zonation of reef biota is evident within well-exposed reefs of the lower reef cluster. Three to four stages are recognizable:1) a low-diversity tabulate coral-dominatedpioneering community including large tabulate coral colonies (halysitids and favositids), and few stromatoporoids (clathrodictyids, ecclimadictyids), fasciculate rugosans, large generally monotypic stalked crinoids, and shelly benthos (brachiopods, few ostracodes and trilobites);2) an intermediate- to high-diversity, mixed tabulate coral-stromatoporoid-dominatedreef-core community;3) a slightly lower diversity stromatoporoid-tabulate coral-dominatedclimax community with laminar coenitids and alveolitids; and,4) in a few localities, a capping, low-diversity tabulatecoral-dominated (alveolitid and coenitid), and stromatoporoid-bearing community comprising laminar forms. Amelioration of Early Silurian climates, following Late Ordovician glaciation, allowed gradual reestablishment of extensive shallow-water reef growth, by mainly new and increasingly diverse genera and species of metazoans. Reef development within the Chicotte Formation coincided with global, widespread development of latest Llandovery and earliest Wenlock reefs in subtropical to tropical areas. Chicotte reefs have broad characteristics, in terms of overall biotic composition, vertical successions recognized, and paleogeographic setting, similar to those of equivalent and slightly younger age from intracratonic settings in Baltica (Gotland, Sweden and Estonia) and central and northern Laurentia (Midcontinent, U.S.A.; Hudson Bay, Canada; and North Greenland, Denmark).     

Late Ordovician-Early Silurian fluctuations in sea level from eastern Anticosti Island, Quebec

Over 1,000 m of Upper Ordovician to Lower Silurian mixed carbonate and clastic strata on Anticosti Island are nearly tectonically undisturbed, despite their proximity to the Northern Appalachians fronting Quebec's Gulf of St. Lawrence. Natural cliffs exposed along the coast and rivers in the eastern part of the island make a relatively conformable sequence belonging to the Ashgill and Llandovery Series. Fossil communities interpreted as depth-associated in life are especially repetitious in the Becscie, Gun River, Jupiter, and Chicotte Formations (Llandovery Series), and to a lesser degree in the Upper Vaureal and Ellis Bay Formations (Ashgill Series). Preliminary study of the pattern of changeovers in Eocoelia, Pentamerus and Stricklandia communities suggests that Anticosti seas deepened and shallowed three and a half times during the Early Silurian. High water peaks were reached during B₁-B₂, C₁-C₂ and C₄-C₅ times, with a final deepening trend beginning in late C₅ time. Age determinations of these events are based on the occurrence of graptolites (with some new records from Anticosti) keyed to the standard graptolite zones, and species of the Eocoelia lineage are also useful for correlation. The profile of the Anticosti sea-level curve compares well with other curves reconstructed from the Lower Silurian of New York, Michigan, and Iowa. Widespread synchronism in sea-level changes on the North American platform is thus corroborated.     

Regional integration of evidence for evolution in the Silurian Pentamerus-Pentameroides lineage

Under ideal conditions, the stratophenetic test for phyletic gradualism in fossil lineages requires nearly continuous samples of time-specific populations through rock sequences representing geologically significant periods of time. Shifting environments account for one source of 'imperfection' in the local rock record. Few species are sufficiently eurytopic to survive changing environments in a given region over a long time span. Where marine fossils are involved, independently correlated sea-level curves may be used to patch together segments of stratigraphic sections from different regions that collectively encompass the uninterrupted environment of the target species. In the Lower Silurian of Iowa, stratigraphic gaps among test samples for phyletic gradualism in pentamerid brachiopods occur wherever pentamerid communities are succeeded by deeper water stricklandiid communities or by shallower-water coral-algal communities. Correlation of sea-level curves indicates that water depth was consistently shallower in the northern Great Lakes area. Usually when stricklandiid communities replaced a pentamerid community in Iowan seas, contemporaneous pentamerid communities replaced a coral-algal community in Michigan or Ontario seas. Temporal meshing of samples from Iowa and the northern Great Lakes area (based on congruent Stricklandia and Eocoelia lineage zones) supports the hypothesis that Pentamerus oblongus evolved to Pentameroides subrectus through a gradual narrowing and loss of divergence in its outer plates. A transitional morphotype between the two genera (from the Lower Silurian of Alabama) is illustrated. □ Phyletic gradualism, punctuated equilibria, Brachiopoda, Pentamerida, Silurian, North America.     

Reef reconstruction after extinction events of the latest ordovician in the Yangtze platform,South China

Summary Early Silurian reef reconstruction on the Yangtze Platform, in the northern part of the South China Block, is preceded by a combination of regional and global processes. During most of Ashgill time (Late Ordovician), the area was dominated by Wufeng Formation deep water graptolitic black shales. Reefs largely disappeard in the middle of the Ashgill Stage, from the northwestern margin of Cathaysian Land (southeastern South China Block), in advance of the Late Ordovician glaciation and mass extinction, due to regional sea-level changes and regional uplift, unrelated to the mass extinction itselt. Late Ordovician microbial mudmound occurrence is also found in the western margin of the Yangtze Platform, its age corresponding to theDicellograptus complexus graptolite biozone of pre-extinction time. On the Yangtze Platform, a thin, non-reef-bearing carbonate, the Kuanyinchiao Formation (=Nancheng Formation in some sites), thickness generally no more than 1m, occurs near several landmasses as a result of Hirnantian regression. Reappearance of the earliest Silurian carbonates consisting of rare skeletal lenses in the upper part of Lungmachi Formation, are correlated to theacensus graptolite biozone, early Rhuddanian of Shiqian, northeastern Guizhou, near Qianzhong Land. Carbonate sediments gradually developed into beds rich in brachiopods and crinoids in the lower part of Xiangshuyuan Formation, middle Rhuddanian. In the middle part of Xiangshuyan Formation, biostromes, containing abundant and high diversity benthic faunas such as corals, crinoids and brachiopods, show beginnings of reconstruction of reef facies. Substantial reef recovery occurred in the upper part of Xiangshuyuan Formation, lower Aeronian, as small patch reefs and biostromes. During the late Aeronian, carbonate sediments, especially reefs and reef-related facies, expanded on the upper Yangtze Platform, and radiation of reefs occurred in Ningqiang Formation, upper Telychian. The long period of reef recovery, taking several million years, remains difficult to explain, because redistribution of any refugia faunas would be expected to take place soon after the extinction. Reefs and reef-related facies subsequently declined after Telychian time due to regional uplift of the major portion of the Yangtze Platform. Carbonate facies are therefore uncommon in South China during the rest of Silurian time.     

Biotic structure and morphology of patch reefs from South China (Ningqiang Formation, Telychian, Llandovery, Silurian)

Summary Ningqiang Formation (late Telychian, Llandovery, Silurian), characterized by nearly 3000 m of shales in tercalated with carbonates, is situated between Ningqiang (S. Shaanxi Province) to Guangyuan (N. Sichuan Province) adjacent to the northwest margin of the Yangtze Platform. The high diversity “Xiushan Fauna”, and abundant reef development, illustrate a relatively warm and persistent shallo marine environment in these early Silurian sediments. The sequence shows reef radiation after recovery from the end Ordovician mass extinction envents. Multiple horizons of reef-building occurred within a relatively short geological interval and resulted in more than 30patch reefs up to 200 m in diameter and 1–50 m vertically, composed of abundant fossils. Reef biota include frame-building corals, stromatoporoids, bryozoans, and microbialites, and reef-associated oranisms such as crinoids, brachiopods, trilobites, gastropods, nautiloids and ostracods. Three reefrelated biotic associations are recognised: a) reefs dominated by framework with crinoids and microbia; b) reefs dominated by only crinoids and microbia; and c) crinoiddomainated facies. Seven representative reef examples illustrate different morphologies and growth styles. A high terrigenous debris input and shallow epicontinental ramp, which lacked obvious topographic variation, were major controls which resulted in rather simple reefs; sedimentation was apparently the main constraint on lateral and vertical extension of reefs, and prevented large-scale reef complexes developing.     

Restudy of some Ordovician–Silurian boundary graptolites from Anticosti Island, Canada, and their biostratigraphic significance

The Ellis Bay Formation on Anticosti Island has long been recognized for the biostratigraphic importance of its latest Ordovician conodont, palynomorph, and shelly fossil assemblages. However, a sparse record of graptolites has made it difficult to correlate these assemblages with the graptolite biozonation. Restudy of some previously described and examination of newly collected normalograptid specimens from the Ellis Bay and lower Becscie formations, however, shows that biostratigraphically important taxa are present and these species provide important constraints on the age of the strata. Normalograptus parvulus and N. minor have been identified in the upper half of the Ellis Bay Formation, suggesting that these strata are late Hirnantian in age ( N. persculptus Biozone). Normalograptus imperfectus and Normalograptus sp. aff. N. acceptus occur in the basal beds of the Becscie Formation, indicating that these strata are earliest Silurian. These graptolite data support the hypothesis that the positive carbon isotope excursion seen in the uppermost strata of the Ellis Bay Formation is isochronous with that seen in the Hirnantian strata at Dob's Linn, Scotland, and does not span much of the lower to mid-Hirnantian, as is the case in Arctic Canada and Nevada, USA.     Anticosti Island , Hirnantian, graptolites, Ordovician, Silurian.     

Euryhalinity of Palaeozoic articulate brachiopods

OMonotypic and very low diversity virgianid shell beds from the Upper Ordovician to Lower Silurian dolomites of North Greenland were formed in marginal marine quiet-water hypersaline environments. In the light of this evidence the salinity tolerances of other Palaeozoic articulate brachiopods is evaluated. There are only a small number of species apparently invading hypersaline or brackish environments, but it is significant considering that previously all articulate brachiopods were thought to be fully marine. Two types of occurrence are noted, those species specifically related to marginally marine environments, disappearing with the introduction of fully marine faunas, and the majority of species which extend their normal marine range into marginal conditions. No brachiopod species appears to have invaded very hypersaline or truly brackish conditions. No single group of articulate brachiopods specifically specialised in colonising marginal marine environments, apart from possibly the virgianid pentamerids. Palaeozoic, Upper Ordovician, Lower Silurian, Brachiopoda. Pentamerida, Virgianidae, Greenland, palaeoecology. hypersaline environments, brackish environments .     

THE COMPOSITION AND STRUCTURE OF LOWER SILURIAN MARINE COMMUNITIES

Five benthic communities occupied the shelf regions of the British Isles, Norway, and North America in Upper Llandovery times. The communities are listed below in order of increasing distance from shore.

• 1 The Lingula Community is the least diverse; it has both infaunal elements, including a protobranch, and two lingulids, and epifaunal elements, including a rhynchonellid, a pterioid, and a cornulitid. A restricted and protected near-shore environment, such as a bay or estuary, is postulated.
• 2 The Eocoelia Community shares elements in common with the former community, but is more diverse and is dominated by epifaunal forms; the many small pedunculate brachiopods probably lived attached to the large leptostrophiid brachiopod.
• 3 The Pentamerus Community is dominated by this genus which lived free and upright on the bottom; smaller pedunculate brachiopods probably attached to this large neighbor.
• 4 The Costistricklandia Community was similar in structure to the former community with the many small pedunculate brachiopods being attached to the large Costistricklandia.
• 5 The Clorinda Community is the most diverse, with a great variety of small brachiopods which were probably able to attach to small objects in this quiet off-shore environment, or to some moderately sized brachiopods, such as Clorinda and Cyrtia, which apparently lived free on the bottom.

The brachiopod dominated communities of the Silurian clearly inhabited the ‘level bottom’, an area now occupied mainly by infaunal forms. The main attachment surfaces for the epifaunal elements of the Silurian communities were disarticulated, convex-upward shells.     

Evolutionary and biogeographical shifts in response to the Late Ordovician mass extinction

The Late Ordovician mass extinction was an interval of high extinction with inferred low ecological selectivity, resulting in little change in community structure after the event. In contrast, the mass extinction may have fundamentally changed evolutionary dynamics in the surviving groups. We investigated the phylogenetic relationships among strophomenoid brachiopods, a diverse brachiopod superfamily that was a primary component of Ordovician ecosystems. Four Ordovician families/subfamilies sampled in the analysis (Rafinesquinidae, Strophomeninae, Glyptomenidae and Furcitellinae) were reconstructed as monophyletic groups, and the base of the strophomenoid clade that dominated the Silurian recovery was reconstructed as diversifying alongside these families during the Middle Ordovician. We time‐calibrated the phylogeny and used geographical occurrences to investigate biogeographical changes in the strophomenoids through time with the R package BiogeoBEARS . Our results indicate that extinction was higher in taxa whose ranges were constrained to tropical or subtropical regions. Furthermore, our results suggest important shifts in the diversification patterns of these brachiopods after the mass extinction. While most of the strophomenoid families survived the Late Ordovician event, ecologically abundant taxonomic groups during the Ordovician were either driven to extinction, reduced in diversity, or slowly died off during the Silurian. The new abundant strophomenoid taxa derived from one clade (consisting of Silurian–Devonian groups such as Douvillinidae, Strophodontidae and Amphistrophiidae) that diversified during the post‐extinction radiation. Our results suggest the selective diversification during the Silurian radiation, rather than selective extinction in the Late Ordovician, had a greater impact on the evolutionary history of strophomenoid brachiopods.