Letteratura scientifica selezionata sul tema "Palaeophytogeography"

The present paper deals with spatial and temporal distribution of pteridophytic megafossils within Palaeozoic plant bearing horizons of India. An attempt has been made to describe the pteridophytic assemblages in various strata of different ages, dynamism of the relative dominance pattern of various types of pteridophytes within each assemblage vis-Ã -vis the environment they lived in. Critical discussion has been done regarding increasing diversity of Palaeozoic pteridophytic taxa, taxonomic riddles, plant architecture, ecological analysis and phylogenetic implications. Special attention has been given to the floristic regionalism of Lower Carboniferous flora of India in reference to the world palaeophytogeography and occurrence of admixture of Cathaysian, Euramerian and Gondwana pteridophytic elements in palaeoecotone zone near the northwestern boundary of Indian Gondwana Plate.

The remarkably preserved Rhynie chert plants remain pivotal to our understanding of early land plants. The extraordinary anatomical detail they preserve is a consequence of exceptional preservation, by silicification, in the hot-springs environment they inhabited. However, this has prompted questions as to just how typical of early land plants the Rhynie chert plants really are. Some have suggested that they were highly adapted to the unusual hot-springs environment and are unrepresentative of ‘normal’ plants of the regional flora. New quantitative analysis of dispersed spore assemblages from the stratigraphical sequence of the Rhynie outlier, coupled with characterization of the in situ spores of the Rhynie chert plants, permits investigation of their palaeoecology and palaeophytogeography. It is shown that the Rhynie inland intermontane basin harboured a relatively diverse flora with only a small proportion of these plants actually inhabiting the hot-springs environment. However, the flora of the Rhynie basin differed from coeval lowland floodplain deposits on the same continent, as it was less diverse, lacked some important spore groups and contained some unique elements. At least some of the Rhynie plants (e.g. Horneophyton lignieri ) existed outside the hot-springs environment, inhabiting the wider basin, and were indeed palaeogeographically widespread. They probably existed in the hot-springs environment because they were preadapted to this unstable and harsh setting. This article is part of a discussion meeting issue ‘The Rhynie cherts: our earliest terrestrial ecosystem revisited’.

Les plantes ont connu une période de diversification intense pendant le Silurien-Dévonien, correspondant à la colonisation progressive des milieux terrestres (440-360 Ma). Néanmoins, le tempo et le mode de cette radiation restent controversés, et les facteurs contrôlant la diversité n'ont pas encore été clairement identifiés. Cette thèse, à travers plusieurs jeux de données de macrofossiles de plantes et via un large éventail de méthodes quantitatives, a permis de caractériser leurs dynamiques spatiales et temporelles. Ce travail évalue également les biais qui peuvent altérer notre perception de cette radiation. Tout d'abord, un modèle à quatre facteurs s'est avéré adéquat pour décrire la structure sous-jacente de la dynamique de diversification des premières plantes. Le modèle suggère des basculements écologiques pendant les phases de transition, corroboré à travers une caractérisation approfondie des patrons globaux de diversité végétale. Cependant, les fluctuations de diversité durant le Silurien-Dévonien dépendent fortement de l'effort d'échantillonnage, bien que plusieurs signaux de diversification et d'extinction semblent en être dissociés. Une étude subséquente à l'échelle continentale a démontré que les lacunes géologiques demeuraient également un élément important expliquant l'allure des patrons apparents de diversité des premières plantes terrestres. Ce biais est difficilement corrigeable même en ayant recours aux méthodes de normalisation de l'échantillonnage les plus avancées. Les divergences paléogéographiques ont ensuite été évaluées afin de mettre en évidence une éventuelle composante spatiale dans la radiation des premières plantes terrestres. Cette analyse a permis de mettre en évidence l'influence du climat sur la distribution et la dispersion de la végétation, notamment lors des périodes les plus froides. Enfin, cette thèse comprend une révision d'un assemblage de plantes fossiles du Dévonien inférieur du nord de la France, fournissant des occurrences taxonomiquement à jour et bien datées qui pourront être intégrées dans des études ultérieures
Plants underwent an extensive Silurian-Devonian diversification during their progressive colonization of terrestrial surfaces (440-360 Ma). Nonetheless, the tempo and mode of this radiation remains controversial, and drivers of diversity have yet to be clearly identified. This thesis, through a series of newly-compiled datasets of plant macrofossils, and via a wide array of quantitative methods, characterizes temporal and spatial dynamics. It further evaluates the biases that may alter our perception of this landmark event. Firstly, a four-factor model was found adequate to describe the underlying structure of early vegetation dynamics. The pattern suggests ecological shifts during transitions phases, further corroborated through an in-depth characterization of global plant diversity patterns. Nevertheless, the general pattern of Silurian-Devonian plant diversity was found to heavily depend on sampling effort, although several signals of diversification and extinction seemed to be dissociated from it, implying real underlying biological signals. A subsequent continental-scale study further demonstrated that, in addition to sampling heterogeneity, geological incompleteness remained an important element in driving apparent early land plant diversity patterns. This bias is not easily corrected even with the most advanced sampling-standardization methods. Furthermore, paleogeographical discrepancies were assessed to uncover a possible spatial component into early land plant radiation. This led to the discovery of a climatologically-driven plant distribution and dispersion, further enhanced during colder periods. Lastly, this thesis includes a review of an Early Devonian plant fossil assemblage from northern France, providing taxonomically up to date and well-dated occurrences to integrate in future studies