Habitats and probable nature of acritarchs from the Upper Riphean Chencha Formation

Morphology and taphonomy of acritarchs from the Upper Riphean deposits of the Baikal Folded Region (eastern Siberia) are analyzed. The morphotypes of acritarchs are compared to various stages in the life cycle of modern green algae of the order Chlorococcales. The acritarchs Dictyotidium minor Stan. and the modern coenobial taxon Pediastrum boryanum (Turp). Menegh. showed the greatest similarity of structure.     

The staminal lever mechanism in Salvia L. (Lamiaceae): a key innovation for adaptive radiation?

Floral key innovations play a significant role in the discussion of adaptive radiation in plants. The paper brings together a brief review of morphological key innovations in plants, elucidating their evolutionary significance in flower–pollinator interactions, and new data on Salvia, a genus being examined as an example for presumed adaptive radiation. We hypothesize that the characteristic staminal lever mechanism functions as a key innovation. It is defined as a functional unit including the modification of stamens to lever-like structures, their reversible movement, and the organization of the remaining floral structures involved in the process of pollen transfer. We follow the assumption that structure and functioning of the staminal levers play a major role in the process of pollen deposition on the pollinator's body, and that minute changes of both their proportions and their interactions with pollinators may have significant consequences for the pollination system. The functioning of the staminal lever mechanism is tested by field investigations, biomechanical experiments and pollination simulations. First results are presented, and possible modes of allopatric and sympatric speciation are discussed, based on morphometry of Salvia flowers and pollinators as well as on the operating mode of the staminal lever mechanism. Special attention is given to species-specific patterns of pollen deposition on the pollinator's body. We assume that, depending on the precision of the lever movement, sympatric Salvia species flowering during overlapping periods and sharing the same pollinating species may be either mechanically isolated from each other or able to hybridize. The latter may result in speciation, as may spontaneous mutations influencing the flower-pollinator interaction, e.g. by significant changes in morphometry of the staminal lever system and/or other flower structures. As a consequence, Salvia individuals may deposit pollen on a different part of the pollinator's body, or even adapt to a new pollinator species, both resulting in reproductive isolation from the parental population.     

Biostratinomy and functional morphology of enrollment in two Middle Devonian trilobites

Although it is common knowledge that many trilobites enrolled, behavioral and functional aspects of enrollment are not at all well understood. Taphonomic details portrayed by enrolled trilobites in the Middle Devonian Hamilton Group (New York State) indicate that enrollment was a complex and morphologically constrained behavior. The trilobites Phacops rana (Green) and Greenops boothi (Green) are frequently enrolled in Hamilton strata; biostratinomic data indicate two very different enrollment postures. Interlocking morphologies (coaptative devices) and apodeme structure and disposition indicate that these postures reflect specific behaviors which involved interaction between tergal structures, inferred musculature, and the substratum. Phacops enrolled by burrowing forward and down into the sediment; dorsal muscles, attached to prominent articulating half-rings, imbricated the thorax such that each lappet overlapped the next posterior segment and locked into a posterior pleural facet. The pygidium was brought into place as the posterior segments of the thorax were placed into vincular notches along the lateral margin of the ventral cephalon. The pygidium locked with the cephalic vincular furrow to complete ‘perfect sphaeroidal’ closure. Greenops enrolled with the cephalon in an upright position at the sediment surface; a submarginal furrow on the ventral surface of the pygidium received the anterior rim of the cephalon. Relatively narrow articulating half-rings limited pleural rotation. Segments were loosely locked into narrow facets at the anterior margin of the next posterior lappet. In spite of rudimentary lappet and half-ring structures, Greenops displays an elaborate system of thoracopygidial muscles which involved dorsoventral and longitudinal attachments along the thorax and into the pygidium. Phacops, in contrast, displays very poorly developed apodemes which occur in the thorax only. Longitudinal muscle strength was likely less important during Phacops enrollment than is evident for the Greenops enrollment procedure. Conversely, Phacops clearly relied to a great degree upon competent closure devices which are poorly developed in Greenops. Biostratinomic data reveal different enrollment behaviors which reflect the function of different enrollment-related morphologies present in each species.     

An Early Miocene Plant Assemblage Severely Influenced By A Volcanic Eruption, Styria, Austria

Sediment and organic facies as well as leaves, pollen, and diaspores co-occurring in a tuffite exposed in Oberdorf (Ko¨flach/Voitsberg lignite area, Styria, Austria) were investigated. The tuffite is distinguishable from the under- and overlying clastic sediments and shows locally normally-graded lapilli, which is assumed to be a sign of direct airfall. The plant assemblage partly resulted from a volcanic eruption that coincided with the season in which many woody plants were flowering; deciduous ones were leafless or in the state of opening their buds; diaspores were not yet developed. Leaves of evergreen woody species, buds/bud scales, and clusters of immature pollen partly with adhering anther material were stripped off their parent plants and quickly embedded in the tuffite. The leaves of deciduous taxa and herbaceous monocotyledons, diaspores, partly also pollen, and organic facies components indicate progressive degradation. Such degraded plant debris probably accumulated in the backswamp sediments prior to the volcanic eruption. The tephra can only be correlated to the 'Lower Rhyolite Tuffs' in the Pannonian Basin (Hungary), indicating a (Late) Eggenburgian/Early Ottnangian age. The new species Ternstroemites waltheri is described. Distylium fergusonii Knobloch and Kvaček and Laurophyllum rugatum Kvaček and Bůžek are first reports from Austria.     

A reconsideration of cf. Psilophyton princeps (Croft & Lang, 1942), a zosterophyll widespread in the Lower Old Red Sandstone of South Wales

EE WARDS, D., KENRICK, P. & CARLUCCIO, L. M., 1988. A reconsideration of cf. P lophyton princeps (Croft & Lang, 1942), a zosterophyll widespread in the Lower Old Rt 1 Sandstone of South Wales. The Lower Devonian plant from Llanover Quarry, Gwent, cal ed cf. Psilophyton princeps , is shown to be a zosterophyll and placed in a new genus. It comprises an ere t planar pseudomonopodial and isotomously branching system of spiny axes with subaxillary pre ections (axillary tubercles) with circinate tips, sometimes replaced by a downwardly directed, spiring, branching axis. Its xylem, strap-shaped in cross-section and exarch, is composed of directly and ndirectly connected annular thickenings. An extended distal fertile zone consists of axes with spot ingia in two opposite or sub-opposite rows. Each sporangium comprises two equal valves, ellip'ical to reniform in face view, and is held upright on a short curved stalk. Dehiscence is around the convex margin which is bordered by a narrow strip of thickening. The Welsh plants are comp ired with other zosterophylls and appear closest to Sawdonia ornata except that they possess sub-axillay branches and lack the characteristic dark-tipped spines. Detailed analysis of coalified mater: and the distribution and fabric of pyrite in permineralizations shows that the original structure of the tracheids was similar to that in Gosslingia and most other zosterophylls, and that the taphonomic processes, with lignified walls preserved as coalified layers and softer tissues replaced by pyrite, were also broadly the same. Permineralizations in pyrite and limonite allow an evaluation of the effects of oxidation of pyrite on original cell structure.     

Patterns of bryophyte associations at different scales in a Norwegian boreal spruce forest

Abstract. Patterns of associations between 36 bryophytes and their relationships with trends in α- and β-diversity were studied at five spatial scales (from 1 m² to 1/256 m²) in a Norwegian boreal spruce forest. The range and dispersion of α-diversity values in the data were significantly higher than in comparable model data sets, indicating varation from favourable to unfavourable conditions for bryophytes at all scales, particularly with increasing cover of the upper layers. The number of positive associations was significantly higher than predicted from a random distribution, for all sample plot sizes except the smallest. For the most frequent species, this number decreased with decreasing sample plot size. The excess of positive associations was due to the presence of (1) α-diversity trends, as demonstrated by a stochastic simulation, and (2) β-diversity (variation along environmental gradients). A microscale coenocline from dominance of large forest floor mosses to small liverworts, is added to two broad-scale coenoclines demonstrated earlier. Facilitation - positive density-dependence caused by more favourable moisture conditions within dense stands - is discussed as a possible third cause of excess positive associations. The number of significant negative associations was generally low, and deviated neither from theoretical values assuming random distribution of species, nor from predicted values accounting for α-diversity trends. The low proportion of negative associations, even in the presence of β-diversity trends, suggests that interspecific competition is not important in this vegetation. Several alternatives to competition are discussed; (1) static mechanisms for avoidance of competition, (2) mobility, and (3) the importance of density-independent mortality, in particular due to fine-scale disturbance. Simulation studies for assessing the effects of α-diversity trends on species associations are emphasized.     

Affinity analysis: methodologies and statistical inference

Affinity analysis (AA) is a group of methods for the study of the variation of degrees of compositional relatedness among all of the communities in a landscape. AA cab be used with statistical inference to compare mosaic diversities (89-1) among different landscapes, identify unusual sites within a landscape, and determine when a pair of sites are significantly different from each other. These procedures were done with a set of samples from meadows in the Danube River Valley near Ulm by using random simulations to provide expectations of the summary statistics. The sampling and statistical limitations of AA were discussed.     

A mineralogical method to determine cyclicity in the taphonomic and diagenetic history of fossilized bones

The study of authigenic minerals within the voids of a fossilized bone can reveal its diagenetic history. When the order of precipitation of minerals is plotted on an Eh/pH diagram any cyclicity in the diagenetic history is revealed. If one cycle is displayed then it can be assumed that the bone has been found in its original bed of deposition; if two cycles or more are revealed then reworking or environmental change may have taken place. This is demonstrated in a case study of two bones from the Wealden Group (Lower Cretaceous) from the Isle of Wight, UK.