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New information pertaining to the biostratinomy of Uintacrinus assemblages has been derived from re-examination of museum collections and analysis of in situ material. Individuals are preserved as thin lenses in dense aggregations with articulated calyces and arms only on the lower surface, in contrast to disarticulated material on the upper surface. Calyces may be imbricated within a lens and are mostly compressed laterally. Specimens also may be preserved oral side up or down. Some specimens displaying the oral side retain soft-part preservation of the tegmen, anal tube, and ambulacra. A thin, jet black organic lamination is visible beneath calyx plates. SEM analysis reveals the presence of possible microbial spherules and filaments on this lamination. Dense aggregations reveal a number of new preservational features, including marginal indentations and lacunae that suggest cohesive behavior of the layer prior to burial. SEM also reveals well-preserved stereom in articulated crinoids on the lower surface, in contrast to the upper surface in which the stereom is apparently infilled with calcium carbonate. Some specimens retain a black, organic lamination within the crinoidal layer itself that may represent remnants of a microbial mat. It is proposed that a microbial mat of necrolytic origin provided cohesion and that microbial sealing during decay may help to explain other instances of similar crinoid preservation, including both benthic and pelagic forms, in which articulation is confined to lower surfaces.
The Cretaceous Two Medicine Formation of northwestern Montana has yielded blocky, calcareous coprolites that contain abundant fragments of conifer wood and were produced by large herbivorous dinosaurs. The coprolites are generally dark gray to black in color due to a dark substance confined chiefly within what originally were the capillaries of tracheid and ray cells of xylem. This substance is a kerogen that consists in part of thin-walled vesicles 0.1–1.3 μm in diameter. Pyrolysis products of this kerogen are diagnostic of a bacterial origin with a possible contribution from terrestrial plants. The vesicular component is interpreted as the residue of bacterial cells, whereas a second filamentous component, closely associated with the vesicles, may be the residue of an extracellular binding material, such as glycocalyx.
At least two episodes of calcification of the coprolite are recognized by manganous cathodoluminescence. The earlier of these infilled the capillary channels of the conifer fragments. Wood cell walls, voids, cracks, and small burrows were filled during the later episode. Microprobe data confirm these results and show that phosphate is sequestered in the capillaries. These observations suggest that bacteria within the capillaries induced initial mineralization of the coprolite, and, in so doing, created barriers that protected organic residues from subsequent destruction. Early onset of mineralization is consistent with the degree of preservation of woody xylem found in the coprolites.
Drilling predation presents a rare opportunity to quantify ecological interactions in the fossil record. Most large-scale studies have focused on temporal rather than spatial patterns. However, spatial variability patterns may both mask secular trends and provide important insights into geographic and environmental gradients in predation. To explore spatial patterns in predation, bulk samples of mollusks were collected from middle Miocene (Burdigalian and Langhian) marine deposits of Europe, including multiple sites from two adjacent bioprovinces: the Boreal Province and Paratethys. Two facies were sampled: fine-grained and coarse-grained siliciclastics. The sampling scheme allows for a comparison of drilling predation at the local scale (within provinces), regional scale (between provinces), and between facies (within and between provinces).
In the Miocene of Europe, statistically significant spatial variations in drilling-predation patterns occur locally, regionally, and among facies (these variations can be either masked or exaggerated when the samples are pooled into coarser analytical groupings). Regardless of the taxonomic resolution of the analysis, inter-regional and facies variation between samples is significant and on occasions exceeds 20%. The sample-level pattern of variation in drilling intensity is notably consistent for pooled data and for each mollusk class, but major differences exist at finer taxonomic scales of families and genera. Escalation parameters (proportion of failed and multiple predatory attacks) also vary significantly between the provinces. In contrast, drill-hole size and site distributions display remarkably consistent patterns across samples regardless of the region, environment, composition of potential prey and predator, observed drilling intensity, and levels of escalation parameters. This suggests that stereotypy in predatory behavior can be displayed by higher taxa and may be independent of the environment, geography, and prey type. The dramatic differences between intensity patterns and stereotypy patterns indicate that the scale and nature of spatial variability may vary notably among different predation parameters. Thus, whereas behavioral stereotypy appears to be stable, the drilling intensity and escalation parameters display variability levels that are comparable to the temporal variations observed among samples collected over evolutionary time scales. The spatial variation in the fossil record of all relevant predation parameters should be evaluated independently, and controlled for, before any large-scale temporal trends are inferred.
Silicified microbes found on the discharge aprons around modern geysers and hot springs commonly appear to be preserved superbly. This can be attributed to their rapid silicification, which often begins while they are alive. In geological terms, therefore, they are silicified instantaneously. Thus, it might be expected that these microbes should be good replicas of the living organisms and, therefore, easy to identify in terms of extant taxa.
Silicified microbes found on the discharge aprons around geysers and hot springs of North Island, New Zealand, are preserved through replacement and/or encrustation. Organic matter is typically absent, and examples of sheaths being partly replaced or coated by other minerals, such as iron oxide, have not yet been recognized. Accordingly, the cellular-level information needed for microbe identification must be gleaned from features preserved in the silica. Unfortunately, the silicification processes commonly destroy and/or disguise most of the taxonomic features that are necessary for reliable identification in terms of extant taxa. Silicification may, for example, obscure the presence of a sheath and/or significantly alter the size of the microbes. The loss and/or modification of such important taxonomic features means that the identification of silicified microbes is fraught with problems and must be approached with caution.
This paper documents a difference in isotopic compositions between Upper Cambrian microbial and non-microbial micritic deposits and proposes implications for diagenesis of calcimicrobial deposits. The δ18O values (−10.98 to −8.71; average −9.88 ‰ VPDB) of calcimicrite comprising shallow subtidal microbialites from the southern Appalachians are more negative than: (1) the calcimicrite from associated subtidal non-microbial deposits (−8.98 to −7.16; average −7.82), suggesting a different diagenetic history; and (2) estimates of Late Cambrian marine calcite values (−5 to −3 ‰), indicating postdepositional modifications. Early diagenetic calcification of microbial deposits promoted the formation of growth cavities and borings rimmed with marine fibrous and prismatic calcite cement. Some of the voids remained open and provided pathways for fluids during later diagenesis. The microbial deposits, therefore, experienced more pronounced diagenetic alteration than the less porous non-microbial micritic deposits. The δ18O compositions provided invaluable insights into the influence of early lithification on the later diagenesis of microbialites and into the processes that can result in poor preservation of syndepositional marine isotope signatures in these deposits.
Polystrata alba (Pfender) Denizot, 1968 (Peyssonneliaceae, Rhodophyta) in Late Eocene algal limestones of the Upper Austrian Alpine Foreland Basin forms (1) horizontal crusts, (2) subspherical and irregular, unilayered rhodoliths with sediment-filled inner cavities, and (3) rhodoliths. Most of the described growth forms are unique and previously have not been described from fossil material. Comparisons with present-day analogues, however, reveal that most growth features can be explained by the interplay between sediment input and bottom stability. This actualistic approach allows the reconstruction of paleoecologic and taphonomic processes that influenced both growth forms of P. alba and the resulting sedimentary facies. The model described in this study provides a useful tool for the reconstruction of paleoenvironmental conditions.
Fossil Marsiliaceae, referable to Marsilea (also known as water clover or pepperwort), were found as impressions in baked claystone (clinker) of the Eocene Wasatch Formation near Buffalo, Wyoming. This is the first documented evidence of Marsilea foliage in Tertiary strata. The fossil is in the Bureau of Land Management's Petrified Tree Environmental Education Area where strata are associated with the Healy and Walters coal beds. Previous palynological analyses, the presence of the ferns Salvinia preauriculata and Lygodium kaulfussi, and the stratigraphic position of the deposits indicate an Early Eocene age for the fossils. Leaf impressions of a variety of pteridophytes and spermatophytes, in conjunction with more than 100 pollen and spore taxa, indicate deposition on a tropical to subtropical fluvial floodplain. Leaf morphology, including leaf size, shape, and venation, are very similar to living species of Marsilea. The preservation in thermally altered sedimentary rock that was derived from claystone is consistent with the plants' current preference for moist clay soils. The conservative morphology and environmental preferences of Marsilea indicate that it is an ecologically conservative genus that can be a reliable indicator of quiet freshwater habitats with clay substrata.