The influence of denitrifying seawater on graptolite extinction and diversification during the Hirnantian (latest Ordovician) mass extinction event

A continuous trench exposure within the uppermost type Vinini Formation at Vinini Creek, Roberts Mountains, Nevada, provides an unparalleled opportunity to examine the fate of graptolites, prominent Paleozoic zooplankton, during most of the Hirnantian mass extinction event. On the basis of a detailed biostratigraphic and sedimentological dataset, the relatively complete extinction record is examined in the context of ecological constraints, and it is found to reflect an ecological collapse driven by glacio-eustatic sea-level fall and associated changes in oceanic circulation. Diverse graptolite populations of the Dicranograptidae-Diplograptidae-Orthograptidae (DDO) fauna, which flourished in denitrifying waters within the oceanic oxygen-minimum zone (OMZ) during sea-level highstand, largely vanished with the loss of these conditions during glacio-eustatic sea-level fall. However, populations of one clade, the normalograptids, which inhabited the oxygenated waters of the photic zone, not only survived but diversified. These survivors gave rise to rapid recolonization and diversification with re-establishment of the oxygen-minimum and denitrifying conditions during post-Hirnantian sea-level rise. This ecological model also applies globally to other well-documented coeval stratigraphic intervals, representing both oceanic and platform sea settings.     

A refined graptolite biostratigraphy for the late Ordovician–early Silurian of central Wales

Morphometric analysis of graptolites from the persculptus and acuminatus biozones of central Wales identifies four successive morphospecies of normalograptids. These graptolites can be used for biostratigraphical subdivision of these strata as follows: (i) an early persculptus Biozone interval containing broad forms with geniculate thecae that have the morphology of Persculptograptus persculptus with an early insertion point for the full median septum (theca 1¹); (ii) a supra‐adjacent level of early persculptus Biozone age, with narrower, parallel‐sided forms, that have been referred to as Normalograptus? aff. parvulus and have a slightly later insertion point for the full median septum (theca 1²); (iii) a third interval, encompassing the later part of the persculptus Biozone to the early acuminatus Biozone, with Normalograptus? cf. parvulus, which has the full median septum delayed to the level of theca 3–7; and (iv) a younger interval, in the mid‐acuminatus Biozone with Persculptograptus cf. persculptus specimens that do not display the median septum on its reverse side. These taxa can be used for refined biostratigraphy and correlation in the late Ordovician and early Silurian of central Wales. The progressive delay in the insertion of the median septum in these taxa may have wider application for the correlation of the interval immediately after the Hirnantian glacial maximum.     

Ecological disruption close to the Ordovician‐Silurian boundary

Following a long period of stability there was substantial ecological disruption in the late Ordovician, accompanied by widespread extinction. The ecological upheaval was spread over a period of time (1 My?) and varied in intensity between different groups.

The greatest change in brachiopod faunas occurred in the tropics, where there were widespread extinctions. In temperate regions the community structure, although disrupted, was not destroyed. The deep shelf associations (Benthic Assemblages 4–5) of the Rawtheyan persisted in an attenuated form into the Hirnantian when they were supplemented by genera of the ”Hirnantia fauna” and then became strongly re‐established in the Llandovery.

Trilobites, in contrast to brachiopods, suffered a worldwide extinction in the late Ashgill. Approximately 40% of trilobite genera became extinct at, or near, the Rawtheyan‐Hirnantian boundary.

Analysis of the distribution of Rawtheyan trilobite and brachiopod genera supports a correlation between geographical distribution and survival. Global range charts for brachiopod and trilobite genera, incorporating ecological and palaeogeographical data, have been compiled for this study.     

华南与缅甸奥陶纪末赫南特贝动物群中的无铰类腕足动物

在奥陶纪末生物大灭绝的两幕之间,海洋底域繁盛着赫南特贝腕足动物群（Hirnantia Fauna）。它数量丰富,分布广泛,历程短暂。以往国内外学者研究这个动物群时,常把有铰类腕足动物作为重点,而无铰类只被简单描述或列出名单,整体面貌不明。无铰类化石尽管材料有限、研究基础薄弱,但只就属的数目而言,占据了全球赫南特贝动物群总属数的近1/5,其群落、演化和环境意义不可小觑。文中专门记述上扬子区（华南古板块）观音桥层（赫南特早中期）与缅甸曼德勒地区（滇缅马苏古地体）Hwe Mawng紫色页岩段（赫南特中期）所产赫南特贝动物群的无铰类化石,计有3目、4超科[Linguloidea（舌形贝超科）、Discinoidea（平圆贝超科）、Craniopsoidea（似髑髅贝超科）和Cranioidea（髑髅贝超科）]的10属、12种,包括5个命名属种[Plectoglossa cf. davidsoni (Barrande),Schizotretinia cf. euxina (Havlí?ek), Pseudopholidops partibilis (Rong),Petrocrania cribrum (Temple),Xenocrania haimei (Reed)]和7个未定种（Trematis sp.,Paracraniops sp.,Acanthocrania sp.,Petrocrania? sp. 1,Petrocrania? sp. 2, Pseudolingula? sp. 和Orbiculoidea sp.）,其中,Pseudolingula? sp.和Orbiculoidea sp.两个未定名种因标本不佳,未正式描述。其中,以Pseudopholidops最为常见,其次是Xenocrania和Petrocrania。前两属是华南、滇缅马苏、波罗的卡、阿瓦隆尼亚、佩鲁尼卡等古板块或地体赫南特贝动物群的常见分子。它们已知限于南、北纬30°之间的低纬度地区,这可能与化石采集和研究程度有关,但更可能反映奥陶纪末全球气候仍存在分异现象。研究识别了奥陶纪晚期无铰类腕足动物7个目,可归为3个类群：灭绝目（仅神父贝目Paterinida）、消减目（多样性与丰度大幅衰减,尤其是三分贝目Trimerellida和乳孔贝目Acrotretida在Hirnantian销声匿迹）和延续目（适应能力强、忍耐阈值高,成功穿越大灾难的首幕）。这些分类单元对研究奥陶纪-志留纪交界期腕足动物群的多样性、群落生态、生物地理及宏演化等有重要意义。     

奥陶—志留系界线地层生物全球对比

详述扬子区晚奥陶世晚期（阿什极期）至兰多维列世初期的生物带序列,修正部分的笔石带,与全球各重要地区进行对比,研究表明,全球奥陶系顶部赫南特亚阶及其上下地层在我国的扬子区发育最好,地层连续发展育并广泛出露,生物带发育齐全,不但有连续的笔石带,而且有世界广布的赫南特贝腕足动物群,有望在我国建立赫南特亚阶的全球层型剖面和点（ＧＳＳＰ）。     

Isolated Chewtonian (Lower Ordovician) graptolites from western Newfoundland

Isolated material of Chewtonian graptolites from the Cow Head Group of western Newfoundland shows some new and unexpected structural details. A high number of the two- and three-stipedPendeograptus fruticosus specimens show metasicular origin for th1¹ combined with a normal isograptid proximal development. Sigmagraptine sicular development includes a large parallel-sided prosicula and a parallel-sided metasicula. One species acquired an azygograptid-like proximal end, characterised by a loss of the initial branching, but kept the capacity to produce distal dichotomies.Maeandrograptus sinosus n. sp. andKeblograptus geminus n. sp. are described as new species.      

华南下扬子区的裂齿鱼类化石——华南二叠系—三叠系界线上下鱼类序列研究之二

重新描述了江苏句容与安徽和县的裂齿鱼类化石 ,将华南下扬子区已记述的 2属 5种裂齿鱼类化石初步修订为 1属 2种———江苏张氏鱼 (Zhanginajiangsuensis)和扬子张氏鱼(Zhanginayangtzensis)。由于目前对裂齿鱼类的系统发育关系所知甚少 ,张氏鱼属的系统位置以及相关的动物地理分布问题仍有待深入的研究。     

Quickly identifying tree species susceptible to extinction: a case study of seven tree species at Northeast China Transect

Quickly predicting which species are most susceptible to extirpation in a defined area is important for conservation and environmental monitoring. We hypothesised that the susceptibility of tree species to extinction in an area could be inferred by the spatial and temporal dynamics of its populations. Here we use change in population size, population spatial variability, spatial autocorrelation, spatial cohesion, crash rate, and recovery rate to characterise the relative susceptibility to extirpation for seven tree species along the Northeast China Transect from 1986 to 1994. Betula dahurica Pall. and Populus davidiana Dode. were found to have a higher susceptibility to loss than Pinus koraiensis Siebold et Zucc., Betula costata Trautv., and Larix olgensis A. Henry in this area during this time period. The same methods could be useful to monitor and predict the susceptibility of species extinction at a larger regional scale.     

Pattern of some Silurian bioevents

The best‐known Silurian bioevent occurred at the end of the Wenlock: the lundgreni event, together with the nassa‐ludensis crisis, was established among planktic graptolites. The East Baltic data show several peaks of high diversity (especially triangulatus, turriculatus, scanicus zones) and three levels of low diversity of graptolites (antennularius, radians, ludensis zones). These are more or less coincident with sea‐level changes. Energetic innovation of the shallow shelf corals started in the early Silurian. The late Wenlock regression seems not to affect them seriously but the late Silurian decline coincides with the aridization of the climate and a regression of the shelf seas. The Agnatha had strong radiations in the Wenlock (ludensis Zone) and Ludlow (leintwardinensis Zone), the fishes in the Pridoli. Many Silurian vertebrates were long‐ranging and extinction rate was relatively low; only at the late leintwardinensis level and in the latest Ludlow did considerable extinctions occur.     

长江三角洲麦／玉米—稻新种植制度高产稳产的生态学原理研究

为在长江三角洲地区发展麦／玉米-稻新三熟种植制度,通过大量的田间试验和生产调查,对该熟制高产稳产的生态学原理进行了系统分析结果表明．春玉米在该地生态适应性较好,麦玉米套作中的作物种间关系以互补为主,三熟制资源利用率提高20％以上,能改善土壤物理性状和农田生态环境,并有内部有机物质投入保障,以及三熟制耐连作是其高产稳产的根本所在．     

黔北晚奥陶世Hirnantian期观音桥层四射珊瑚新资料及其地质意义

报道黔北毕节、仁怀和石阡地区晚奥陶世Hirnantian期观音桥层中首次发现的四射珊瑚Axiphoria,Bodophyllum,Dalmanophyllum,Leolasma,Brachyelasmaunicum(Neuman),Grewingkiaanguinea(Scheffen),结合前人报道的该层所产的Borelasma,Kenophyllum,Streptelasma,Ullernelasma等属,进一步表明黔北观音桥层四射珊瑚动物群与斯堪的纳维亚(Scandinavia)、中亚、阿尔泰地区同期珊瑚群关系密切。该动物群对阐明晚奥陶世四射珊瑚古地理关系具有重要意义。黔北观音桥层四射珊瑚十分丰富,总计有18属39种。文中共描述10属12种,其中1新属3新种,即AmplexobrachyelasmaHeetChengen.nov.,GrewingkiadensicolumnaHeetChensp.nov.,KenophyllumfossulatumHeetChensp.nov.,LeolasmaqianbeienseHeetChensp.nov.。