贵州安顺募役剖面晚二叠世腕足动物群落及其生态特征*

本文对贵州募役剖面长兴期腕足动物群进行了系统分类鉴定和古生态分析,发现其与前人所报道的华南同时期腕足动物群存在着显著的差别,以Spiriferellina为绝对优势属,包含少量华南长兴期的常见分子,如Fusichonetes、Araxathyris和Peltichia等。募役剖面的腕足类化石主要产自碎屑岩层位,与华南同期碎屑岩相剖面的腕足动物群落相比,该动物群中的优势分子个体较大、壳体较厚且发育较粗大的壳疹,这可能与长兴期募役剖面动物群所处的特殊栖息地环境(浅水碳酸盐岩台地与深水硅质碎屑岩盆地之间的过渡地带)有关。二叠纪末期大规模的火山作用导致水体中碎屑物质含量增加,影响腕足类的滤食效率,而募役剖面清澈、水动力弱的水体环境,为滤食性的腕足动物提供了有利的环境条件。最后,通过与华南长兴期不同沉积相区腕足动物群落(六枝剖面、稻堆山剖面、中寨剖面、新民剖面、马家山剖面和仁村坪剖面群落)的对比分析,发现募役剖面腕足动物群与毗邻的六枝剖面腕足动物群在属级组成上的相似度较高,且过渡岩相栖息地环境下的腕足动物群在生物灭绝事件前也呈现出高优势度、低均匀度的群落结构特征,指示海洋底栖生物群落已经先于二叠纪末期生物集群灭绝事件出现了早期危机信号。     

An ecologically mixed brachiopod fauna from Changhsingian deep-water basin of South China: consequence of end-Permian global warming

The Late Permian Shaiwa Group of the Ziyun area of Guizhou, South China is a deep-water facies succession characterized by deep-water assemblages of pelagic radiolarians, foraminifers, bivalves, ammonoids and brachiopods. Here we report 20 brachiopod species in 18 genera from the uppermost Shaiwa Group. This brachiopod fauna is latest Changhsingian in age and dominated by productides. The palaeoecologic and taphonomic analysis reveals that the brachiopod fauna is preserved in situ. The attachment modes and substratum preference demonstrate that the Shaiwa brachiopod fauna comprises admixed elements of deep-water and shallow-water assemblages. The presence of the shallow-water brachiopods in the Shaiwa faunas indicates the involuntary settlement of shallow-water brachiopods. The stressed ecologic pressure, triggered by warming surface waters, restricted ecospace and short food sources, may have forced some shallow-water elements to move to hospitable deep-water settings and others to modify their habiting behaviours and exploit new ecospace in deep-water environments. We infer that the end-Permian global warming and subsequent transgression event may have accounted for the stressed environmental pressure in the shallow-water communities prior to the end-Permian mass extinction.     

Diversity and extinction patterns of permian brachiopoda of South China

The stratigraphical and geographical distribution of 851 brachiopod species from 216 genera and 65 families in the Permian of South China are analysed. It is revealed that the brachiopod diversity underwent two sharp falls during the Permian. The first occurred at the end of Maokouan, accompaning the widely recognised, extensive regression across the Maokouan‐Wujiapingian boundary. Fifty‐seven species of 29 genera survived this first major extinction event. The second sharp reduction of brachiopod diversity took place in the later Changhsingian, with only 17 Permian‐type brachiopod species of 12 genera straggling into the earliest Triassic. Detailed stratigraphic analysis shows that more than 90% of the Changhsingian brachiopod species disappeared at different levels in the Changhsingian before the widely perceived end‐Permian ‘mass extinction’ occurred. It is also notable that each of the step‐wise diversity reduction events was apparently heterochronous. In view of the evidence from lithologies, faunal components and geochemical analyses, the two sharp falls of Permian brachiopod diversity in South China are considered to be closely related to multiple interactions of an environmental deterioration caused by large‐scale regressions.     

Latest Ordovician brachiopod and trilobite assemblage from Yuhang,northern Zhejiang,East China: a window on Hirnantian deep-water benthos

A moderately diverse brachiopod and trilobite assemblage, the Leangella–Dalmanitina (Songxites) Assemblage, occurs in the upper Yankou Formation (Hirnantian, probably equivalent to the Normalograptus persculptus Biozone) at Shizi Hill, Yuhang, west of Hangzhou, northern Zhejiang, E China. The brachiopods are rare, characterised by minute, thin shells with very small body cavities, preserved in mudstones as moulds. They may have inhabited quiet, deep-water and dysaerobic slope environments with low levels of nutrients, equivalent to Benthic Assemblage 5. Most genera were adapted for life in deep water and either remained there or alternatively migrated into relatively shallower habitats to evade perturbations during the first phase of the end Ordovician extinctions. The slope environments were recolonised from outer shelf and upper slope communities during the early Hirnantian, but isolated biotas may also have survived in deeper-water habitats by reducing their population size and diversity during the crisis. The Leangella–Dalmanitina (Songxites) Assemblage provides an unique Hirnantian window through which we can monitor the changes in the deep-water biofacies following the first phase of the extinctions. Significantly, parts of the deep water marine environment may have survived intact, the end Ordovician extinctions.     

华南贵州宾夕法尼亚亚纪牙形类Neognathodus动物群:演化及地层对比意义

以华南斜坡相的罗甸纳庆剖面为代表,我国石炭纪宾夕法尼亚亚纪早–中期地层建立起了基于多个属种的牙形类分带,并可与全球其他地区同期地层进行广泛对比。Neognathodus属是这一时期一类常见的浅水相牙形类分子,在北美、东欧等地的浅水相地层中被广泛用作地层划分对比标志。该属分子在我国北方地区浅水相地层中是重要的带化石分子,而在华南斜坡相剖面中占比非常低。结合现有的生物地层框架,本文厘清了华南贵州罗甸附近3条斜坡相剖面中Neognathodus属分子的延限,尝试利用牙形类P1分子齿台的对称特征将其演化过程归纳为五个阶段,并提出阶段4中对称分子(如:N. bothrops, N. colombiensis, N. nataliae等)的再次出现可作为全球莫斯科阶底界的辅助对比标志。     

Kissinella-Christiania Associations in the early Ashgill Foliomena brachiopod fauna of South China

A new ecological unit within the well-documented late Ordovician brachiopod Foliomena fauna is defined on the basis of assemblages from Northern Cuizhou and southern Sichuan. Southwest China. The Kassinella-Chrisriania Association, from the lower Ashgill Linhsiang and Chientsaokou formations, is dominated by the eponymous genera together with species of mainly Dedzetina, Sericoidea and Kozlowskites Foliomena is rare or absent. To date, the Foliomena fauna has been documented only from deep-water environments however, the new association apparently occupied shallower depths, probably in lowermost Benthic Assemblage Zone 3 and uppermost Benthic Assemblage Zone 4, presumably at the shallow end of the depth range of the Foliomere fauna. The incursion of the Foliomena fauna into relatively shallow-water environments may have been encouraged by abnormally low oxygen levels and sparse nutrients together with persistent soft substrates across this part of the Yangtze Platform during the early Ashgill. *** Ordovician, Ashgill, China, brachiopods. F oliomena fauna.     

贵州交榜留茶坡组化石组合特征及其生物地层学和演化意义*

埃迪卡拉纪—寒武纪之交见证了地球—生命系统不同圈层的重大变革, 是复杂多细胞生物演化的重要转折期。华南是开展相关研究的主要区域之一, 但前人工作主要集中在化石材料丰富的浅水台地相区, 深水区生物组成面貌尚未得到充分认识。本研究对斜坡相区贵州交榜剖面的留茶坡组进行了详细研究, 通过酸蚀和薄片观察发现了丰富的化石材料, 包括: 海绵骨针、软舌螺、可能的原牙形类(? Protohertzina sp.)和织金钉类(? Zhijinites sp.)、球形疑源类、Megathrix longus, 及不同类型的多细胞藻类, 亲缘关系未定的Poratusiramus sp.、球形化石和形态多样的丝状、片状化石等。该化石组合属于寒武纪纽芬兰世幸运期, 其中的骨骼化石以海绵骨针为主。化石组合中既有与浅水区共有分子, 也有深水区特有类群, 丰富了斜坡相区的化石记录, 具有潜在的地层对比和演化意义。     

Evolution,palaeoecology, and palaeobiogeography of the Late Ordovician–Early Silurian brachiopod Epitomyonia

Epitomyonia is characterized by various types of dorsal ridges, which may be transverse, longitudinal, or highly convoluted and probably served as skeletal supports for lophophores of various complexity. Multivariate analyses suggest that the Epitomyonia-bearing brachiopod associations lived in relatively shallow-water environment in the Late Ordovician, and inhabited mainly deep-water environments in the early Wenlock. The temporal and spatial change in the faunal distribution may be explained by three alternative scenarios: (1) Epitomyonia followed the broad evolutionary trend of the Palaeozoic Evolutionary Fauna to shift from shallow- to deeper-water settings over time; (2) the dicoelosiid communities could not compete with the large-shelled pentameride communities in continental shelf settings during the Early Silurian; or (3) only the shallow-water Epitomyonia died out in the Late Ordovician mass extinction event, whereas some poorly known deep-water Late Ordovician forms survived into the Early Silurian. Epitomyonia paucitropida n. sp. from the lower Whittaker Formation (late Katian) of the Mackenzie Mountains, northwestern Canada, is reported as the first known Ordovician species of Epitomyonia from the palaeocontinent of Laurentia, characterized by a small shell with weak, transverse dorsal ridges that are most primitive for the genus.     

Survival patterns of macrobenthic marine assemblages during the end-Permian mass extinction in the western Tethys (Dolomites, Italy)

The ecological competition between brachiopods and bivalves is analysed by means of a quantitative palaeoecologic method applied on four assemblages located within a short stratigraphic interval, approximately 2 m thick, in the lower Tesero Member of the Werfen Formation (in the Southern Alps). The assemblages originate from the Tesero, Bulla and Sass de Putia sections. The analysed stratigraphic interval, uppermost Changhsingian in age, is located between the early and heaviest phase of the end-Permian mass extinction, which occurred across the Bellerophon/Werfen formational boundary (Event Boundary), and the Permian/Triassic boundary (Chronological Boundary), when nearly all the Permian stenotopic holdovers disappeared.These assemblages are characterised by small sized skeletons (“Lilliput effect”), which represent an adaptive survival strategy in stressed and harsh habitats resulting from the climatic and palaeoceanographic changes connected with the mass extinction. The Tesero assemblages are dominated by rhynchonelliform brachiopod Orbicoelia (bed CNT10) or Streptorhynchus (bed CNT11A), which were mostly attached at the top of shallow microbialitic mounds. These assemblages are again dominated by Permian stenotopic taxa and show a Palaeozoic structure. The Tesero habitat, which again permitted the survival of brachiopods, represented one of the last refuges in the western Tethys. On the contrary, the Bulla (BU9-10) and Sass de Putia (wPK13A) assemblages are bivalve-dominated, and thus show an ecologic structure typical of Early Triassic post-extinction marine benthic communities or Palaeozoic stressed marine communities. The bivalve-dominated assemblages proliferated in prevailing muddy siliciclastic substrates, with brief episodes of microbial algal growth. The most important environmental limiting factors and leading causes of end-Permian mass extinction are discussed in terms of palaeoautecologic and palaeosynecologic analysis.The different taxonomic composition and ecologic structure of the assemblages is related to palaeogeography, including water depth and connections with the open sea. The brachiopod-dominated assemblage, exclusive of the Tesero section, proliferated in microbial carbonate habitats in near-shore environments. The bivalve-dominated assemblages, which were more widespread than the brachiopod assemblages in the Dolomites and also occurred in other western Tethys localities, occur in more open and deeper marine environments. In the western Tethys margins, the local distribution of mixed faunas suggests that the extinction of Permian stenotopic taxa was caused by the onset of poisonous water on the shelves originating from deep marine environments.This extinction pattern appears to be a regional phenomenon and does not seem be applicable on a global scale. The extinction events were controlled by a complex network of interactive factors and the survival of faunal elements was probably stochastic.     

Late Permian marine ecosystem collapse began in deeper waters: evidence from brachiopod diversity and body size changes

Analysis of Permian–Triassic brachiopod diversity and body size changes from different water depths spanning the continental shelf to basinal facies in South China provides insights into the process of environmental deterioration. Comparison of the temporal changes of brachiopod diversity between deepwater and shallow‐water facies demonstrates that deepwater brachiopods disappeared earlier than shallow‐water brachiopods. This indicates that high environmental stress commenced first in deepwater settings and later extended to shallow waters. This environmental stress is attributed to major volcanic eruptions, which first led to formation of a stratified ocean and a chemocline in the outer shelf and deeper water environments, causing the disappearance of deep marine benthos including brachiopods. The chemocline then rapidly migrated upward and extended to shallow waters, causing widespread mass extinction of shallow marine benthos. We predict that the spatial and temporal patterns of earlier onset of disappearance/extinction and ecological crisis in deeper water ecosystems will be recorded during other episodes of rapid global warming.     

Coral assemblages, biofacies, and ecological zones in the mid-Holocene reef deDosits of the Enriquillo Valley, Dominican Republic

Stemann, T. A. & Johnson, K. G. 1992 07 15: Coral assemblages, biofacies. and ecological zones in the mid-Holocene reef deposits of the Enriquillo Valley, Dominican Republic. A large, subaerially exposed mid-Holocene reef in the Enriquillo Valley (southwest Dominican Republic) provides an excellent opportunity to examine the relationship between reefal ecology and reefal deposits. Coral species richness and diversity in the Enriquillo reef are comparable to that found in the recent of the Caribbean, and ecological zonation comprised of a shallow-water branching coral zone and a deeper water mixed-coral zone is apparent. Similar zonation and diversity patterns have been recognized on living Caribbcan reefs with moderate wave exposure. Three statistically discrete biopdcies can be discriminated in the Enriquillo deposits using quadrat point-counting techniques commonly used to census modern reefs. They include a facies dominated by Acropora cervicornis, a low diversity assemblage with abundant, large colonies of Siderastrea siderea and Stephanocoenia intersepta, and a higher diversity assembbdge composed of various taxa including Montastraea spp., Colpophyllia spp., and Agaricia spp. Each facies can be recognized at scales of 1–3 m², though in some cases they extend for more than 20 m². In general, the A. cervicornis facies is spatially segregated from the other two biofacies. although neither the shallow nor the deep-water ecological zone is comprised of a single reef biofacies. Rather, the biofacies described here appear to represent distinct micro-environments resulting from ecological variation at a subzonal scale. Micro-environments of similar scale are most likely preserved in other reef deposits. Recognition of these subzonal biofacies may have important consequences for the stratigraphical and paleoccological interpretation of fossil reefs. Corals, biofacies, reef zonation, coral communities, fossil reefs.     

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.     

The Permian/Triassic mass extinction among brachiopods in the Northern Caucasus (northern Palaeo-Tethys): A tentative assessment

A palaeontological record of the Northern Caucasus provides new data to evaluate the influence of the Permian/Triassic mass extinction on brachiopod communities. The study region is currently located in the southwest of Russia; it laid on the northern margin of the Palaeo-Tethys Ocean during the late Paleozoic-early Mesozoic. A total of 168 genera and 36 superfamilies are known from the Changhsingian-Bajocian deposits of this region. The total diversity of brachiopods was very high in the Changhsingian (57 genera and 19 superfamilies), but these organisms disappeared entirely at the Permian/Triassic boundary. Three genera and three superfamilies existed in the Induan, but brachiopods perished again in the Olenekian. A recovery began in the Anisian, but the Changhsingian diversity was never reached again. No genera crossed the Permian/Triassic boundary, whereas 4 superfamilies became able to do this. Ambocoelioidea was a “dead clade walking” and went extinct in the Induan, whereas three other superfamilies (Dialasmatoidea, Rhynchonelloidea, and Wellerelloidea) were more successful. Survivors included no less than 20% of genera during the entire Induan-Bajocian time interval. The Changhsingian-Anisian interval is dominated by just one type of facies in the studied region, which may explain differences in the post-extinction diversity patterns between the Northern Caucasus, South China, and other parts of the World. Use of the alternative Triassic time scale does not change the absolute duration of the post-extinction stress (5.1 myr), whereas it highlights higher rates for the Anisian recovery (appearance of 0.9 superfamilies and 2.8 genera per myr).     

Diversity–productivity relationships in two ecologically realistic rarity–extinction scenarios

To develop a better understanding of how biodiversity loss and productivity are related, we need to consider ecologically realistic rarity (i.e. reduced evenness and increased dominance) and extinction (i.e. reduced richness) scenarios. Furthermore, we need to identify and better understand the factors that influence species and community yielding behaviors because the general conditions for overyielding are the same as those for coexistence. We established experimental tallgrass prairie plots in Iowa to determine how two ecologically realistic rarity–extinction scenarios influenced aboveground net primary productivity (ANPP) and disassembly. Equal‐mass seedlings of six tallgrass prairie species were transplanted into field plots to establish realistic declining species evenness (high, medium, low) and richness (4, 1) treatments. Across declining evenness treatments, the relative abundance of the ubiquitous tall species Andropogon gerardii increased, the relative abundance of the tall species Salvia azurea was constant, and the relative abundance of two short (dissimilar height scenario) or two tall species (tall scenario) decreased. Monocultures of Andropogon represented a continuation of this trend until there was complete dominance by Andropogon and extinction of all other species. Our treatments also allowed us to test if variation in plant height contributes to the complementarity effect. Niche partitioning in plant height was not positively related to complementarity. The effects of declining species evenness and richness on the diversity–productivity relationship were different for these two ecologically realistic rarity–extinction scenarios. Specifically, as diversity declined across treatments, ANPP and the selection effects decreased in tall communities, but not in dissimilar communities. Additionally, differences between these two scenarios revealed that decreased species yielding behavior is associated with two tallgrass prairie extinction risk factors, rarity and short height. The differences between these scenarios demonstrate the importance of incorporating the known patterns of diversity declines into future studies.     

Competition in slow motion: the unusual case of benthic marine communities in the wake of the end‐Permian mass extinction

Changes of community structure in response to competition usually take place on timescales that are much too short to be visible in the geological record. Here we report the notable exception of a benthic marine community in the wake of the end‐Permian mass extinction, which is associated with the microbial limestone facies of the earliest Triassic of South China. The newly reported fauna is well preserved and extraordinarily rich (30 benthic macroinvertebrate species, including the new species Astartella? stefaniae (Bivalvia) and Eucochlis obliquecostata (Gastropoda)) and stems from an environmentally stable setting providing favourable conditions for benthic organisms. Whereas changes in the taxonomic composition are negligible over the observed time interval of 10–100 ka, three ecological stages are identified, in which relative abundances of initially rare species continuously increased at the cost of previously dominant species. Concomitant with the changes of dominant species is an increase in faunal evenness and heterogeneity. In the absence of both environmental and taxonomic changes, we attribute this pattern to the long‐term effects of interspecific competition, which acted at an unusually slow pace because the number of competing species and potential immigrants was dramatically reduced by the end‐Permian mass extinction. We suggest that these non‐actualistic conditions led to decreased rates of niche differentiation and hence to the delayed rediversification of benthos that characterizes the aftermath of the greatest Phanerozoic mass extinction event. A hyperbolic diversification model is proposed, which accounts for the positive relationship between the intensity of interspecific competition and the rate of niche differentiation and resolves the conundrum of delayed rediversification at a time when niche space was largely vacated.     

Latest Guadalupian brachiopods from the Guadalupian/Lopingian boundary GSSP section at Penglaitan in Laibin, Guangxi, South China and implications for the timing of the pre-Lopingian crisis

A brachiopod fauna comprising nine species in eight genera from three closely spaced stratigraphic horizons of the same stratigraphic section is described for the first time from the Laibin Limestone in the uppermost part of the Maokou Formation in the Guadalupian/Lopingian (G/L) GSSP section at Penglaitan, Guangxi Autonomous Region, South China. The brachiopod assemblages are bracketed between two conodont zones: Jinogondolella xuanhanensis Zone below and Jinogondolella granti Zone above and, therefore, they can be safely assigned to the latest Capitanian in age. However, all but one of the nine brachiopod species from the Laibin Limestone carry strong early Lopingian (Wuchiapingian) aspect. Thus, the discovery of this brachiopod fauna not only suggests that some Lopingian brachiopod species had already appeared in the late Guadalupian (Capitanian); more importantly, it has also highlighted the fact that both the previously noted pre-Lopingian life crisis (or end-Guadalupian or Middle Permian mass extinction) and Lopingian recovery/radiation actually occurred in late Capitanian times, sometime before the G/L chronostratigraphic boundary. So far, the Penglaitan GSSP section provides the highest-resolution disappearance patterns of different fossil groups around the G/L boundary.     

Large extinctions of articulate brachiopods in the paleozoic and their ecological and evolutionary consequences

The largest Paleozoic extinctions of articulate brachiopods occurred at the Frasnian—Famennian boundary in the Late Devonian and at the Permian—Triassic boundary. Both extinctions affected taxa of all levels, including orders, but differed in scale, course, and ecological and evolutionary consequences. The Frasnian—Famennian extinction event was selective and evolutionary activity after the crisis varied in different orders. However, in the Early Carboniferous, the brachiopod diversity was mostly restored in comparison with the Devonian maximum. In particular groups, preadaptation played a role in changes in diversity and reconstruction of communities. The brachiopod composition at this boundary changed sharply. The extinction event at the end of Permian was global and accompanied by changes in the biota. Later, in the Meso-Cenozoic, the brachiopod diversity was not restored, and bivalves acquired primary importance in various bottom communities of different sea zones where Paleozoic brachiopods previously dominated. Extinction of brachiopods at this boundary was long and gradual. The symptoms of the ecological crisis in the development of Permian brachiopods are recognized beginning from the Roadian Age, which was probably the onset of this crisis.     

New Early Carboniferous and Bashkirian Ammonoids from the eastern slope of the South Urals

In the Early Carboniferous-Bashkirian the most diverse ammonoid assemblages were associated with deep-water settings of the outer shelf and the carbonate platform slope. At the end of the Early Bashkirian, ammonoid assemblages of basins of the eastern slope of the South Urals were associated with shallow-water settings and bioherm buildups, which probably contributed to their endemism. New species of the genera Neogoniatites, Schartymites, and Stenoglaphyrites are described from localities of the eastern slope of the South Urals.     

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.