Miospore evolution from the Ordovician to the Silurian

The definition of the term cryptospore is amended to include only spores thought to be produced by embryophytes and to exclude all enigmatic palynomorphs. Cryptospores are included here in the miospore group.The oldest published assemblage of typical cryptospores is Llanvirn in age. The evolution of cryptospore assemblages is very slow from the Llanvirn to the early Llandovery. The Telychian and Sheinwoodian stages are periods of drastic impoverishment in cryptospore biodiversity, followed by an important modification in miospore assemblages. This step in the evolution of the vegetation is correlated with the rapid transgression of seas on the continent during the early Llandovery. On the other hand, the Hirnantian glaciation does not affect diversity of the miospore assemblages.     

Taxonomy and palaeoecology of the mollusc Pterotheca from the Ordovician and Silurian of Scotland

A large sample of the bizarre bellerophontiform mollusc Pterotheca from the Upper Llandovery Wether Law Linn Formation in the Scottish Pentland Hills shows marked polymorphic asymmetry. A survival strategy that presents to a predator a mosaic of different search images is suggested to account for the marked variability of the Pterotheca morphology. Multivariate comparisons with Pterotheca mullochensis from the Llandovery of Girvan, P. simplex from the Caradoc of Girvan, P. cf. simplex from the Caradoc of the Northern Belt of the Southern Uplands and P. aff. mullochensis from the Llandovery in the Pentland Hills have helped clarify the morphological differences between these groups. A new species, Pterotheca trimerelloides , is established for the specimens from the Pterotheca beds in the Wether Law Linn Formation. □ Mollusca, Silurian, Ordovician , Pterotheca, taxonomy, palaeoecology.     

Absolute depths of Silurian benthic assemblages

A variety of evidence can be used to estimate the absolute depth of the well-established depth gradient of Silurian onshore-to-offshore benthic assemblages (BA 1–5); this evidence is reviewed herein. There is a fair degree of consistency between fossil benthic assemblages and the occurrence of certain primary sedimentary structures, particularly those involved in storm deposition. A second, probably stronger, line of evidence for absolute depth of Silurian benthic assemblages involves the distribution of fossils of light-sensitive organisms and of reefs. Among these, the most important are the calcified dasycladacean algae, to which the cyclocrinitids of the Middle Ordovician - Early Silurian may belong. The modem dasycladaceans have a narrowly restricted bathymetric range. Maximum depth for modern calcified dasycladaceans is about 90 m, but the vast majority occur at 30 m or less. Some Silurian occurrences of these algae are abundant, particularly in BA 3 and 4; rarely, small specimens of cyclocrinitids and receptaculitids are found in the lower, outer portions of BA 4 and even into 5. This evidence constrains much of the spectrum (BA 1–5) of Silurian fossil communities to a rather narrow depth range, within the photic zone. Based on taxonomic uniformitarianism, we would place the depth of Silurian BA 1 through 4 between 0 and about 40–60 m. The common coincidence of the lower end of storm wave base and the lower end of the photic zone near the BA 4–5 boundary also suggests that this position may represent water depths on the order of 50 m. Several other lines of evidence -including algal borings, widths of facies belts, separation of communities by basalt flows whose thicknesses are known - also support a relatively shallow depth range for BA 14. The absence of storm-disturbed beds over large parts of several major platforms below about the BA 3–4 boundary region suggests that major storms of the Silurian may have been far weaker than those of the present, possibly owing to a different climatic regime. □Absolute depth, Silurian, photic zone, calcareous algae, Benthic Assemblage, storms.     

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.     

New species of stromatoporoidea from the Upper Ordovician and Silurian of the Subpolar Urals

Stromatoporoidea are widespread in the Upper Ordovician and Silurian beds of the Kozhim River (western slope of the Subpolar Urals). Five new species Cystostroma prodigiosum sp. nov., Stylostroma flabellatum sp. nov., Labechiina arguta sp. nov., Ecclimadictyon faveolatum sp. nov., and Araneosustroma astroplexum sp. nov. are described.     

The Ordovician acritarch genera Tranvikium and Ampullula: their relationship and taxonomy

A restudy of the Ordovician (Arenig-Llanvirn) acritarch taxa Tranvikium polygonale Tynni, 1982, and Ampullula suetica Righi, 1991, indicates that they represent extremes in a single morphological plexus. At one extreme are forms with a polar 'excystment' aperture (closed by an operculum or two opercular pieces) and a smaller opening (plugged or open) at the opposite pole; at the other are forms lacking a polar aperture but having, at the opposite pole, a tube open distally and plugged or open basally. New morphological terms for these structures are proposed. The genera and species are treated as synonyms and an emended diagnosis is given for Tranvikium polygonale, incorporating this whole morphological plexus. The possible purposes of the structures exhibited and the likely affinity of T. polygonale to various groups of algae are discussed. The emendation of Ampullula by Brocke (1997) is rejected and the genus Stelomorpha Yin, 1994 retained, with an emended diagnosis. The new combination Stelomorpha princeps (Brocke, 1997) Uutela and Sarjeant is proposed.     

Upper Ordovician and Lower Silurian chitinozoans from central Nevada and Arctic Canada

Late Ordovician and Early Silurian chitinozoans from the uppermost Vinini Formation, and the Hanson Creek Formation in central Nevada and the lower Cape Phillips Formation, Cape Manning section, in Arctic Canada have been re-investigated and a new chitinozoan biozonation is proposed. The Upper Ordovician of central Nevada can easily be correlated to that of Arctic Canada through the common occurrence of the Ordochitina nevadensis biozone in both regions. No such correlation, however, is possible with the Late Ordovician of Anticosti Island in eastern Canada because of the absence of the index Upper Ordovician chitinozoan zonal species of central Nevada such as Belonechitina tenuispinata sp. nov, Ordochitina nevadensis sp. nov. and Nevadachitina vininica gen. nov., sp. nov. in the former area.One new genus, Nevadachitina, and nine new species, Eisenackitina ripae, Belonechitina martinica, Nevadachitina vininica, Nevadachitina praevininica, Ordochitina nevadensis, Belonechitina tenuispinata, Belonechitina parvispinata, Tanuchitina laurentiana, Angochitina hansonica are described and illustrated in this paper and four species are left in open nomenclature.     

Epithelial moulds from some Upper Ordovician acrotretide brachiopods of Ireland

Three new genera of acrotretid brachiopods are of general morphological interest in that they display polygonal mosaics on the internal shell surfaces, features which are believed to be moulds of the outer epithelial cells. The mosaic is further noted in a specimen of Eoconulus , a form which may also belong to the Acrotretacea. Such mosaics have not previously been recorded from the Acrotretacea. Polygonal mosaics, epithelial moulds, outer epithelium , Eoconulus, Acrotretacea, Ordovician.     

Island benthic assemblages: With examples from the Late Ordovician of Eastern Australia

The Benthic Assemblage (B.A.) concept, developed by A.J. Boucot two decades ago principally for continental marine margins, is extended to offshore island settings. Characteristics of modern island biotas, including ecological displacement, and the effects of r and K selection, can be identified in Late Ordovician volcanic islands of central New South Wales. Two variants of B.A.1 are represented, a quiet‐water lingulide biofacies, and a rough‐water rhynchonellide biofacies. The quiet‐water Eodinobolus biofacies occupied a B.A.1–2 position, onshore of and sheltered by a Tetradium wave‐baffle (B.A.2). The offshore shelfal high diversity strophomenide biofacies is equivalent to B.A.3. Remnants of periplatformal B.A.4–5 communities are recognised in allochthonous limestone breccias which were displaced downslope into graptolitic B.A.6 sediments. Steeper offshore gradients, typical of islands, laterally compress the B.A. profiles, and also contribute to downslope slumping. Ecological displacement in island environments results in extension of the habitat range of species into adjacent B.A.s. Reefs complicate the usual B.A. profile by introducing distinct sheltered and turbulent water environments. These characteristics may have applicability in interpretation of islands throughout the Palaeozoic record.     

A nearshore–offshore trend in acritarch distribution from the Early–Middle Ordovician of the Yangtze Platform, South China

The stratigraphical interval of the late Early Ordovician Didymograptus deflexus and the early Middle Ordovician Azygograptus suecicus graptolite Biozones was investigated from seven sections from the upper Yangtze Platform, southern China. These are located on different parts of the platform, between the nearshore environments of the Kunming area, Yunnan Province, and the offshore carbonate shelf of the Yichang area, Hubei Province. The assemblages recovered from the different parts of the platform vary both in terms of diversity and composition. The nearshore environments show low diversity assemblages with about 10 acritarch species, whereas the offshore shelf environments reflect higher diversities with about 40 species. The composition of the assemblages also changes from simple morphologies (micrhystrids, leiosphaerids, fusiform acritarchs) in nearshore environments to specimens with longer and more complexly branched processes on the shelf. The polygonomorph acritarchs are common over all the upper Yantze Platform, while the acanthomorph genera Baltisphaeridium and Peteinosphaeridium are the most abundant taxa on the offshore carbonate shelf area. Phylogenetic or sea-level changes are probably not responsible for the compositional and diversity changes that occurred during the investigated interval. This study confirms previous interpretations that poorly diversified Palaeozoic acritarch assemblages occur in neritic environments and more complex, highly diversified assemblages are found on the shelf.     

Agars of Gelidiella acerosa of west and southeast coasts of India

Seventeen agar samples were extracted from Gelidiella acerosa (Forsskal) Feldmann and Hamel (Rhodophyta, Gelidiales) specimens collected from nine different sites on the Indian coast-five from southeast coast and four from the west coast. The agar samples were analysed. The stability characteristics of the gels of selected agar samples were studied by rheometry under applied stress conditions, i.e. variation of the storage (G') and loss moduli (G') were studied under varying frequency and duration (time) of the stress applied. Yield, apparent and dynamic viscosities, gelling and melting temperatures, 3,6-anhydrogalactose (3,6-AG), sulphate contents and TGA (Thermogravimetric Analysis) measurements of the products were done. It was observed that the best quality agar was produced by G. acerosa occurring in the Gulf of Mannar region in the southeast coast. The gel strengths and the viscosities of agars extracted from Gelidiella acerosa occurring in the Gulf of Mannar ranged from 500 to 700gcm(-2) and 33 to 45cP for 2001 collections and for 2002 collections the corresponding values were 450 to 845gcm(-2) and 55 to 67cP respectively. On the other hand, for the agar samples extracted from the west coast of India, the gel strength and viscosities values ranged from 225 to 400gcm(-2) and from 15 to 30cP, respectively. The agars obtained from G. acerosa collected from southeast coast have been found to be suitable for bacterial culture and molecular biology. This is the first report of superior quality of agar from the Indian agarophytes.     

Gradient versus cluster analysis of fossil assemblages: a comparison from the Ordovician of southwestern Virginia

Studies in modern ecology indicate that most species are distributed independently along environmental gradients according to their individual requirements. Steep gradients often produce species associations separated by discontinuities; gradual gradients produce broadly-overlapping distributions. Approaching the distribution of species populations as a continuum, using gradient analysis, avoids artificial subdivision of totally intergrading distributions, yet permits discontinuities to emerge where present. Faunas of the Martinsburg Formation (Ordovician) in southwestern Virginia offer an excellent opportunity to test the applicability of gradient analysis in a paleoecological setting. A broad spectrum of environments, from nearshore to open-marine, clastic to carbonate-dominated facies, provide both temporal and geographic variation against which to evaluate changes in species distributions. Variations of five classical, Petersen-type communities were recognized in the Martinsburg using cluster analysis: (1) Lingula, (2) bivalve, (3) Rafinesquina, (4) Onniella, and (5) Sowerbyella-dominated communities. Two gradient analysis techniques, ordination and Markov analysis, revealed the same basic associations. However, ordination and Markov analysis permit arrangement of these associations along one or more interpreted environmental gradients. Factors related to water depth and distance from clastic source areas, particularly bottom stability and disturbance frequency, appear to have been the most important of a complex of interrelated physical parameters. The high-stress, nearshore end of the Martinsburg gradient complex was occupied by a Lingula association, followed seaward by an association of bivalves adapted to less-stressed environments. Low-stress, open-shelf environments were occupied by Rafines-quina, Onniella, or Sowerbyella-dominated associations. Broad overlaps among these articulate brachio-pod associations reflect variations in the open-shelf habitat.     

Zoosporic true fungi and heterotrophic straminipiles assemblages from soil of Brazilian Cerrado areas

The influence of seasonal fluctuations and environmental factors on the occurrence and distribution of zoosporic true fungi and heterotrophic straminipiles in terrestrial ecosystems is poorly understood. This contribution analyses the species composition, frequency, abundance and diversity of zoosporic true fungi and heterotrophic straminipiles assemblages from two areas of Cerrado in the State of São Paulo, Brazil. Samples of soil were collected at four dates during the rainy and dry seasons. Twenty-one abiotic factors were measured. The assemblages showed a high diversity and evenness and were represented by 30 taxa of Chytridiomycota and Oomycota. Some abiotic factors appeared to have influenced the patterns of distribution and occurrence of the taxa in different areas and/or seasons. Even so, the biotic factors (richness, diversity indices and evenness) and the Sorensen index showed high similarity between the assemblages.     

Microtopography and the organization of two assemblages of coral reef fishes in the west indies

Two walls of Salt River Canyon, St. Croix, U.S. Virgin Islands are at the same depth in the fore reef environment and are separated by only 100 m, but they differ in microtopography. Replicate visual censuses of the fish assemblages on these two walls, by four saturation divers, gave consistent estimates of the species assemblages on the two walls. Significant faunal differences between the two walls are best understood in terms of combined features of coloration, predator avoidance, and feeding habit displayed regularly by individuals occupying a given microhabitat. It appears that characteristic sets of environmental circumstances occur within a habitat with sufficient frequency to give a consistent direction to natural selection, producing the patterns we have observed. Thus, form and function is predictable in relation to microhabitat, although species occurrence is not. The “order” and “chaos” concepts of community structure in coral reef fish, with their narrow focus on the predictability of species occurrence, underemphasize the possibility for a simple and direct role for natural selection in shaping the functional characteristics of an assemblage on a small scale     

Fish assemblages on sunken vessels and natural reefs in southeast Florida,USA

Derelict ships are commonly deployed as artificial reefs in the United States, mainly for recreational fishers and divers. Despite their popularity, few studies have rigorously examined fish assemblages on these structures and compared them to natural reefs. Six vessel-reefs off the coast of southeast Florida were censused quarterly (two ships per month) to characterize their associated fish assemblages. SCUBA divers used a non-destructive point-count method to visually assess the fish assemblages over 13- and 12-month intervals (March 2000 to March 2001 and March 2002 to February 2003). During the same intervals, fish assemblages at neighboring natural reefs were also censused. A total of 114,252 fishes of 177 species was counted on natural and vessel-reefs combined. Mean fish abundance and biomass were significantly greater on vessel-reefs in comparison to surrounding natural reef areas. Haemulidae was the most abundant family on vessel-reefs, where it represented 46% of total fish abundance. The most abundant family on natural reefs was Labridae, where it accounted for 24% of total fish abundance. Mean species richness was significantly greater on vessel-reefs than neighboring natural reefs and also differed among vessel-reefs. Both mean fish abundance and mean species richness were not significantly different between natural reefs neighboring vessel-reefs and natural reefs with no artificial structures nearby. This suggests the vessel-reefs are not, in general, attracting fish away from neighboring natural reefs in our area. Additionally, economically important fish species seem to prefer vessel-reefs, as there was a greater abundance of these species on vessel-reefs than surrounding natural reef areas. Fish assemblage structure on natural versus artificial reefs exhibited a low similarity (25.8%). Although no one species was responsible for more than 6% of the total dissimilarity, fish assemblage trophic structure differed strikingly between the two reef types. Planktivores dominated on vessel-reefs, accounting for 54% of the total abundance. Conversely, planktivores only made up 27% of total abundance on natural reefs. The results of this study indicate vessel-reef fish assemblages are unique and that these fishes may be utilizing food resources and habitat characteristics not accessible from or found at natural reefs in our area. Production may also be occurring at vessel-reefs as the attraction of fish species from nearby natural reefs seems to be minimal. Electronic supplementary material Supplementary material is available for this article at and accessible for authorised users     

Crinoid holdfasts from the Silurian of Gotland

Crinoid holdfasts occur throughout the Silurian sequence of Gotland, with a marked concentration to reefs and immediate reef surroundings. Four morphological groups are recognized: (1) Discoid holdfasts. (2) Cirriferous holdfasts, represented by (a) Rhizocrinus -like holdfasts, (b) large radices with stout, often branching cirri, and (c) rhizoid holdfasts, formed by a complicated net of pseudocirri. (3) Creeping stems attached to the substrate by thin strands of stereome. (4) Coiling stems. Discoid attachments, cirriferous holdfasts (types b and c) and coiling stems show little preference to substrate and adapt morphologically to conditions at hand. Rhizoid holdfasts display the greatest variation and apparently occur within many different groups of crinoids. Rhizocrinusttke holdfasts have been found only in quiet-water deposits, while creeping stems were concentrated to more turbulent environments. Coiling stems were epizoic, attached to rugose corals, bryozoans, crinoid stems and similar supports. Growth, mode of life (attached or free), settling and fixation of larvae, and relation to substrate and other organisms ate discussed.     

Potassium accretion byPinus contorta on oligotrophic peat in the west of Ireland

Summary A 22-year-old crop ofPinus contorta on oligotrophic peat was found to contain 85 kg ha^–1 more K than adjacent unplanted areas. It is suggested that the forest cover aids in conserving rainfall derived K which in the natural (unplanted) state is lost to drainage.     

Wall ultrastructure of an Ediacaran acritarch from the Officer Basin, Australia

Well-preserved organic-walled microfossils referred to as acritarchs occur abundantly in Ediacaran deposits in the Officer Basin in Australia. The assemblages are taxonomically diverse, change over short stratigraphical intervals and are largely facies independent across marine basins. Affinities of this informal group of fossils to modern biota are poorly recognized or unknown, with the exception of only a few taxa. Morphological studies by use of transmitted light microscopy, geochemical analyses and other lines of evidence, suggest that some Precambrian acritarchs are related to algae (including prasinophytes, chlorophytes, and perhaps also dinoflagellates). Limitations in magnification and resolution using transmitted light microscopy may be relevant when assessing relationships to modern taxa. Scanning electron microscopy reveals details of morphology, microstructure and wall surface microelements, whereas transmission electron microscopy provides high-resolution images of the cell wall ultrastructure. In the light of previous ultrastructural studies it can be concluded that the division of acritarchs into leiospheres (unornamented) and acanthomorphs (ornamented) is entirely artificial and has no phylogenetic meaning. Examination of Gyalosphaeridium pulchrum using transmission electron microscopy reveals a vesicle wall with four distinct layers. This multilayered wall ultrastructure is broadly shared by a range of morphologically diverse acritarchs as well as some extant microalgae. The chemically resistant biopolymers forming the comparatively thick cell, together with the overall morphology support the interpretation of the microfossil as being in the resting stage in the life cycle. The set of features, morphological and ultrastructural, suggests closer relationship to green algae than dinoflagellates.