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.     

The Ordovician Biodiversification: revolution in the oceanic trophic chain

The Early Palaeozoic phytoplankton (acritarch) radiation paralleled a long-term increase in sea level between the Early Cambrian and the Late Ordovician. In the Late Cambrian, after the SPICE δ¹³C_carb excursion, acritarchs underwent a major change in morphological disparity and their taxonomical diversity increased to reach highest values during the Middle Ordovician (Darriwilian). This highest phytoplankton diversity of the Palaeozoic was possibly the result of palaeogeography (greatest continental dispersal) and major orogenic and volcanic activity, which provided maximum ecospace and large amounts of nutrients. With its warm climate and high atmospheric CO₂ levels, the Ordovician was similar to the Cretaceous: a period when phytoplankton diversity was at its maximum during the Mesozoic. With increased phytoplankton availability in the Late Cambrian and Ordovician a radiation of zooplanktonic organisms took place at the same time as a major diversification of suspension feeders. In addition, planktotrophy originated in invertebrate larvae during the Late Cambrian–Early Ordovician. These important changes in the trophic chain can be considered as a major palaeoecological revolution (part of the rise of the Palaeozoic Evolutionary Fauna of Sepkoski). There is now sufficient evidence that this trophic chain revolution was related to the diversification of the phytoplankton, of which the organic-walled fraction is partly preserved.     

Evolution of ecospace occupancy by Mesozoic marine tetrapods

Ecology and morphology are different, and yet in comparative studies of fossil vertebrates the two are often conflated. The macroevolution of Mesozoic marine tetrapods has been explored in terms of morphological disparity, but less commonly using ecological‐functional categories. Here we use ecospace modelling to quantify ecological disparity across all Mesozoic marine tetrapods. We document the explosive radiation of marine tetrapod groups in the Triassic and their rapid attainment of high ecological disparity. Late Triassic extinctions led to a marked decline in ecological disparity, and the recovery of ecospace and ecological disparity was sluggish in the Early Jurassic. High levels of ecological disparity were again achieved by the Late Jurassic and maintained during the Cretaceous, when the ecospace became saturated by the Late Cretaceous. Sauropterygians, turtles and ichthyosauromorphs were the largest contributors to ecological disparity. Throughout the Mesozoic, we find that established groups remained ecologically conservative and did not explore occupied or vacant niches. Several parts of the ecospace remained vacant for long spans of time. Newly evolved, radiating taxa almost exclusively explored unoccupied ecospace, suggesting that abiotic releases are needed to empty niches and initiate diversification. In the balance of evolutionary drivers in Mesozoic marine tetrapods, abiotic factors were key to initiating diversification events, but biotic factors dominated the subsequent generation of ecological diversity.     

The relation of Late Ordovician glaciation to the Ordovician-Silurian changeover in North American brachiopod faunas

Sheehan, P. M.: The relation of Late Ordovician glaciation to the Ordovician-Silurian changeover in North American brachiopod faunas.
The Ordovician-Silurian changeover of brachiopod faunas in North American epicontinental seas involved the abrupt extinction of endemic Late Ordovician stocks and subsequent repopulation of North American seas by Old World taxa. The Late Ordovician Gondwanaland glaciation may have lowered sea levels sufficiently to place severe stress on the widespread shallow marine faunas in North America, resulting in their eventual extinction. The Late Ordovician depositional history in North America is not well enough known to establish the presence of a latest Ordovician regression, but the earliest Silurian was an interval of off-lap in North America. Therefore, the glacial lowering of sea level is considered to be the most likely cause of the faunal changeover.     

Facies distribution patterns of some marine benthic faunas in early paleozoic platform environments

Worldwide Late Cambrian—Silurian lithofacies patterns indicate that the platforms of that time were sites of accumulation of two essentially different rocks suites: the platform carbonate rocks and the platform terrigenous rocks. Most of the platform rocks accumulated as sediments in shallow marine environments similar to those of the present but far more widely spread.Present-day marine benthic faunas are distributed in depth zones which are primarily controlled by temperature. Faunas tend to occur in substrate-related discrete clusters (communities) within each life zone; similar substrates in different depth zones commonly have different faunal associations. Individual phyletic stocks may encounter environmental optimum or near-optimum conditions in certain areas, that commonly are revealed by an abundance of species and individuals within species in each stock. Environmental optimum conditions depend upon availability of food that may be utilized, modes of feeding of the animals present, water motion, and substrate, among other factors. Organisms in past seas were distributed in patterns similar to those of the present.Carbonate platforms were particularly widespread during the latest Cambrian—Early Ordovician. Intertidal environments spread widely across those platforms during that time and characteristic faunal associations developed in them. Saukiid and related tribolites dominated latest Cambrian carbonate platform intertidal faunas. The Early Ordovician carbonate platform intertidal was dominated by archeogastropod-nautiloid cephalopod faunas. These animals were joined by tabulate corals and certain brachiopods during the latter part of the Ordovician and Silurian as prominent faunal elements in the carbonate platform intertidal—shallow subtidal. Cruziana and related trace fossils, bivalves, and certain tribolites (notably homalonotids and dalmanitids) dominated most terrigenous platform intertidal—shallow subtidal faunas of the Ordovician and Silurian.Articulate brachiopods (primarily orthoids, strophomenoids, and rhynchonelloids) appear to have been relatively prominent during the Early Ordovician in shallow subtidal environments on both carbonate and terrigenous platforms and to have spread down the bathymetric gradient into increasingly deeper subtidal areas of both platforms during the latter part of the Ordovician. Tribolites dominated faunas in relatively moderate to deep subtidal environments on both platforms during the early part of the Ordovician. They were gradually replaced by brachiopods in first the shallower, and later the deeper subtidal as dominant members of the faunas. Brachiopods (primarily pentameroids and spiriferoids) dominated nearly all Silurian warm-water subtidal environments from the shallow subtidal to the edges of the platforms.Platform uplifts in the Middle Ordovician and glacio-eustatic sea-level fluctuations in the Late Ordovician caused environmental changes across the platforms that were accompanied by marked replacements among marine benthic faunas in all environments. The distribution of Ordovician carbonate platforms and glacial deposits suggests that an Ordovician polar region may have been close to present-day equatorial Africa and that Ordovician warm temperate-tropical regions lay close to the present-day North Pole.     

New information on the morphology and skeletal ultrastructure of the Ordovician cyclostome bryozoanKukersella Toots, 1952

PalZ - Well preserved specimens ofKukersella from the Late Ordovician (Ashgill Series) of South Wales have enabled a re-evaluation of the morphology and skeletal ultrastructure of the genus. They...     

Palaeoecology and diversity of endosymbionts in Palaeozoic marine invertebrates: Trace fossil evidence

Endosymbionts are organisms that live within the growing skeleton of a live host organism, producing a cavity called a bioclaustration. The endosymbiont lives inside the bioclaustration, which it forms by locally inhibiting the normal skeletal growth of the host, a behaviour given the new ethological category, impedichnia. As trace fossils, bioclaustrations are direct evidence of past symbioses and are first recognized from the Late Ordovician (Caradoc). Bioclaustrations have a wide geographic distribution and occur in various skeletal marine invertebrates, including tabulate and rugose corals, calcareous sponges, bryozoans, brachiopods, and crinoids. Ten bioclaustration ichnogenera are recognized and occur preferentially in particular host taxa, suggesting host-specificity among Palaeozoic endosymbionts. The diversity of bioclaustrations increased during the Silurian and reached a climax by the late Middle Devonian (Givetian). A collapse in bioclaustration diversity and abundance during the Late Devonian is most significant among endosymbionts of host coral and calcareous sponge taxa that were in decline leading up to the Frasnian-Famennian mass extinction.     

Symbiotic interactions in the Silurian of Baltica

Thirteen symbiotic associations occur in the Silurian of Baltica. Symbiosis was especially prominent among colonial animals, most commonly with stromatoporoids. These sponges hosted the most diverse fauna of endobiotic symbionts (including rugosans, Syringopora, ‘polychaetes’, cornulitids and lingulids). This pattern can be explained by the abundance of stromatoporoids in the Silurian of Baltica and their large skeletal volume, making them attractive hosts for smaller invertebrates. There is an evolutionary trend of an increasing number of different pairs of symbiotic taxa from the Llandovery to the Ludlow, with a remarkable increase in the Ludlow. This is likely related to an increase in the number of mutualistic taxa that could have had evolutionary advantages over organisms less amenable to symbiosis. The number of different pairs of symbiotic taxa also increased in the Wenlock, which may be linked to delayed recovery from the end‐Ordovician mass extinction.     

The effects of the final stages of the Late Ordovician glaciation on marine palynomorphs (chitinozoans, acritarchs, leiospheres) in well Nl-2 (NE Algerian Sahara)

Palynomorph assemblages, especially chitinozoans and acritarchs, from the Upper Ordovician of well Nl-2 (north-east of the Algerian Sahara) are studied in order to precisely date the ultimate effects of the Late Ordovician glaciation and to document the impact of this major climatic stress on the diversity of the palynoplankton. References are made to stable isotope excursions and to global eustatic sea level variations in order to improve the local age determination. The Hassi el Hadjar Formation, i.e. glacio-marine diamictites, is interpreted as a transgressive event resulting from the melting of the northern Gondwana ice cap. It yields poorly preserved and moderately diverse chitinozoans of late Hirnantian age. Acritarchs are more abundant in the lower part of these "microconglomeratic clays", but display a low diversity and are badly preserved throughout the whole formation. Reworked individuals are recorded in both groups. The marine sediments of the M'Kratta Formation of latest Hirnantian age contain better preserved, more abundant and more diverse palynomorph assemblages, especially in the Upper Member. The composition of this palynoplankton indicates a fairly good faunal and phytoplankton recovery after the early Hirnantian climatic stress.The extinction of the Ordovician forms, and the appearance of Silurian type taxa occur only in the uppermost Hirnantian, i.e. following with a slight delay the glacial event. The overlying black shales of Wenlock age (lower part of the Oued Mehaiguène Formation) are indicative of marine anoxic environments. They yield a virtually exclusive, but enormous number of Tasmanacea. The very peculiar composition of this palynoplankton seems to be independent of the Late Ordovician glaciation and is most likely related to the factors that, later, generated and maintained anoxic conditions in this area.A new species of chitinozoan, Spinachitina oulebsiri sp. nov. from the latest Hirnantian M'Kratta Formation, is described and illustrated.     

The oldest bryozoan reefs: a unique Early Ordovician skeletal framework construction

Adachi, N., Ezaki, Y. & Liu, J. 2011: The oldest bryozoan reefs: a unique Early Ordovician skeletal framework construction. Lethaia, Vol. 45, pp. 14–23. The oldest bryozoan reefs occur in the Lower Ordovician (late Tremadocian) Fenhsiang Formation of the Three Gorges area, South China. These reefs show a unique type of bryozoan (Nekhorosheviella) framework, and were constructed as follows: the first stage involved colonization by lithistid sponges, which acted as a baffler to trap sediments, providing bryozoans with a stable substrate for attachment. The bryozoans then grew as an encruser on the surfaces of sponges, showing a preferential downwards and lateral growth within the sponge scaffolding to avoid biological and physical disturbance. Finally, these biotic combinations among skeletal organisms formed a rigid, three‐dimensional skeletal framework. This mode of bryozoan growth in association with lithistid sponges is remarkable and unique in its growth direction, and the appearance of such reefs, just prior to the widespread development of skeletal‐dominated reefs as part of the Great Ordovician Biodiversification Event, provides an excellent example of the earliest attempts by skeletal organisms to form frameworks by themselves. This find significantly enhances our understanding of the initial stages of skeletal‐dominated reef evolution and the ensuing development of reefs during the Middle–Late Ordovician. □Bryozoa, Early Ordovician, lithistid sponge, Ordovician radiation, reef.     

The Devonian nekton revolution

Klug, C., Kröger, B., Kiessling, W., Mullins, G.L., Servais, T., Frýda, J., Korn, D. & Turner, S. 2009: The Devonian nekton revolution. Lethaia, 10.1111/j.1502‐3931.2009.00206.x Traditional analyses of Early Phanerozoic marine diversity at the genus level show an explosive radiation of marine life until the Late Ordovician, followed by a phase of erratic decline continuing until the end of the Palaeozoic, whereas a more recent analysis extends the duration of this early radiation into the Devonian. This catch‐all approach hides an evolutionary and ecological key event long after the Ordovician radiation: the rapid occupation of the free water column by animals during the Devonian. Here, we explore the timing of the occupation of the water column in the Palaeozoic and test the hypothesis that ecological escalation led to fundamental evolutionary changes in the mid‐Palaeozoic marine water column. According to our analyses, demersal and nektonic modes of life were probably initially driven by competition in the diversity‐saturated benthic habitats together with the availability of abundant planktonic food. Escalatory feedback then promoted the rapid rise of nekton in the Devonian as suggested by the sequence and tempo of water‐column occupation. □Devonian, diversity, ecology, food webs, nekton, plankton, radiation.     

Late Jurassic soft-bodied wood epibionts preserved by bioimmuration

While the encrustation of floating driftwood by pseudoplankton has attracted much debate, the utilization of benthic xylic substrata by sessile organisms has received scant attention. Here we record a benthic woodground fauna, including weakly mineralized and entirely soft-bodied taxa, which have been preserved within the cement of an overgrowing oyster. This process, bioimmuration, is ubiquitous in marine hard-substrate communities but is recorded here on a xylic substrate for the first time. Comparison of bioimmured communities will allow investigation of changes in woodground fauna through time and offers the potential for a fuller understanding of the effect of substrate texture on community composition.     

Middle–Late Ordovician brachiopods from Ningnan,southern Sichuan Province,Southwest China: Implications for macroevolution and palaeogeography

Middle to Late Ordovician brachiopods from the Huadan Formation (upper Darriwilian–Sandbian) of Ningnan County, southern Sichuan Province, are systematically documented here for the first time. The locality belongs to the western margin of the Upper Yangtze Platform, South China palaeoplate, and the brachiopod fauna includes one new genus and three new species as well as five other constituents: Hingganoleptaena sp., Acculina zhongliangziensis n. sp., Ningnanmena longisepta n. gen. n. sp., Kassinella (Trimurellina) minuta n. sp., Lepidorthis typicalis Wang, 1955, Protoskenidioides weixinensis Zhan and Jin, 2005, Porambonites transversus Xu, Rong and Liu, 1974, and Psilocamerella sp. Taxonomically it is a typical representative of a Middle to early Late Ordovician brachiopod fauna, and, together with some other evidence from other fossil groups like trilobites, conodonts, chitinozoans, a late Darriwilian–Sandbian age could be inferred for the horizon yielding this fauna. According to the richness of each constituent, this fauna is suggested to be called the Acculina-Ningnanmena fauna (ANF). Numerical palaeogeographical analysis shows that two broad palaeobiogeographic provinces could be recognized during this particular time interval, and, although the ANF is grouped into the South China cluster, it shares very little similarity with other representatives of that group except for two cosmopolitans. It further confirms that the Great Ordovician Biodiversification Event (GOBE), in other words the Ordovician radiation, was actually manifested by the strong localization of major marine organisms such as brachiopods, trilobites, graptolites, etc.     

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。     

Palaeoenvironmental aspects of Late Ordovician Sericoidea shell concentrations in an impact crater,Tvären,Sweden

Frisk, Å.M. & Harper, D.A.T. 2010: Palaeoenvironmental aspects of Late Ordovician Sericoidea shell concentrations in an impact crater, Tvären, Sweden. Lethaia, Vol. 44, pp. 383–396. Numerous studies have reported the presence of the small, thin‐shelled cosmopolitan rhynchonelliformean Sericoidea as being environmentally controlled and, together with its close relatives, characteristic of deep‐water, distal, clastic Ordovician and Silurian settings. Assemblages of Sericoidea have been analysed from post‐impact strata in a newly formed Late Ordovician impact crater. In the crater succession, colonization of benthic faunas can be monitored through the post‐impact limestone, demonstrating a number of environmental preferences. Consequently, the crater, as a result of its restricted area, provides an experimental arena for faunal distributions to be correlated with specific environments. The continuous infilling of the crater following its formation reveals a transition from argillaceous mudstones to carbonates deposited in deeper‐water environments to shallower regimes. Rhynchonelliformean brachiopods inhabited the crater depression very late after the impact and are entirely represented by the genus Sericoidea, occurring abundantly in the upper third of the existing crater infill. The deep‐water regime that existed in the depression during the initial interval of crater formation had been substantially reduced. Clearly Sericoidea‐bearing associations associated with shaly substrates did not merely favour and occupy deep‐water environments as previously suggested. The unfavourable conditions triggered by the impact and the inhospitable aftermath allowed Sericoidea to exploit a less‐crowded ecospace. This reorganization, following the catastrophe, from a deep‐water related ecological niche to considerable shallower settings suggests that Sericoidea was a pioneer colonist displaying an opportunist r‐strategy. The shell beds analysed are related to shallower water and this may, moreover, help unravel the dilemma of the general absence of Sericoidea in the deeper‐water Foliomena fauna. □Dalby Limestone, impact crater, Late Ordovician, opportunists, Sericoidea, Tvären.     

Biotic diachroneity during the Ordovician Radiation: evidence from South China

The Ordovician radiation was one of the most marked and sustained increases in Phanerozoic biodiversification; nevertheless it occurred against a background of minimal global climatic and environmental perturbations. Detailed investigations of the Ordovician successions on the Yangtze Platform of the South China palaeoplate indicate that: (1) the brachiopod α- and β-diversity changes are diachronous; (2) macroevolutionary patterns were different across the South China palaeoplate, with the Early Ordovician brachiopod radiation first occurring in normal marine, shallow-water environments and then moving gradually to both nearer-shore and offshore locations; (3) the main contributors to the initial Ordovician brachiopod radiation were the Orthida and Pentamerida; the typical Ordovician brachiopod fauna, dominated by the Orthida and Strophomenida, did not appear until the late Mid Ordovician (Undulograptus austrodentatus Biozone) when the Strophomenida apparently replaced the dominant position of the Pentamerida within the fauna; (4) different ecotypes (e.g., sessile benthos, mobile benthos together with pelagic and planktonic organisms) demonstrate substantially different macroevolutionary patterns. The Ordovician brachiopod radiation of South China was apparently earlier than that suggested by global trends together with the data available from other palaeoplates or terranes, which may be related to its unique palaeogeographic position (peri-Gondwanan terrane gradually moving to equatorial latitudes).     

THE SKELETON SPACE: A FINITE SET OF ORGANIC DESIGNS

The structures of animal skeletons converge repeatedly on a limited number of architectural designs that can be constructed by growing organisms and that are functionally viable, although often not optimal. Properties of materials, construction rules that determine patterns of development, and physical constraints exerted by the requirements of function suggest that organic structure must necessarily approach these recurrent elements of design. A set of potential designs for the elements of animal skeletons is derived in terms of geometric and construction rules and the properties of materials. Skeletons of actual living and extinct organisms are matched with the possibilities defined within this theoretical morphospace. This provides a metric of skeletal complexity and of the extent to which various groups of animals have been able to exploit the range of possibilities of organic structure. These analyses show that the most evolutionarily advanced animals within a given phylum do not have the most complex skeletons; that arthropods are less morphologically diverse than vertebrates and molluscs; that the physical constraints of life on land and in the air substantially limit the variety of skeletal structures suitable for life in these environments; and that overall the range of possible skeletal designs has been very fully exploited by living and extinct organisms. These results strongly support the hypothesis that the essential elements of organic design are inherent in the material properties of the universe. The organizational properties of animal skeletons suggest that their design elements are fixed point attractors, structures that we characterize as topological attractors that evolution cannot avoid.     

Controls on marine animal biomass through geological time

Total animal biomass depends on four factors: (1) food supply, (2) the efficiency with which animals consume available food, (3) the efficiency with which animals convert consumed food into biomass, and (4) the rate at which animals lose biomass to the environment through respiration or death. Each of these factors may change through geological time because each is a function of animal ecology and physiology. Animal ecology and physiology, in turn, are products of interacting evolutionary and environmental factors. The direction of change in animal biomass through time may be predicted given knowledge of environmental and ecological change. At a finer level, physiological differences among phyla or other higher taxa suggest that they would have had differential responses to specific environmental changes. Physiological features shared by all of life, such as the dependence of metabolic rate on ambient temperature, suggest that even a coarse time‐series of relative changes in animal biomass may enrich understanding of biogeochemical cycling among all organisms, including phytoplankton and microbes. Changes in the abundance of skeletal material in shallow marine deposits through geological time indicate that the biomass of benthic skeletal invertebrates has fluctuated significantly on timescales from millions to hundreds of millions of years. During the Ordovician radiation, increase in the complexity of animal food webs and increase in the efficiency of animal communities in removing available food from the water column and sediment appear most likely to account for a secular increase in animal biomass. Decrease in animal biomass after the end‐Permian extinction appears to have been driven by a combination of factors but particularly decreased aggregate growth efficiency and consumption efficiency. Comparing biomass and diversity trends through other major transitions in the history of animal life has the potential to shed light on the relationship between physical environmental change and ecosystems evolution.     

Ordovician and Silurian brachiopods from graptolitic shales and related deep-water argillaceous rocks

Ordovician and Silurian graptolitic shales and deep-water mudstones contain a sparse fauna of clustered, minute shells which are commonly believed to have been epiplankton attached to seaweed. Modern deep-water organisms may preferentially attach to local firm areas on the soft sediment. It is suggested that the Ordovician and Silurian shells may also have been benthic animals attached to local firm regions of the sea floor. These substrates might have included algal fronds which had fallen to the bottom.