Taphonomie des plantes et interprétations paléoécologiques. Une synthèse

The taphonomy is a powerful and requisite tool for environmental reconstructions of ancient plant communities. Necrobiotic processes, which lead to the production of plant fragments, inform us on fossil plant physiology. Among the processes that can be drawn from necrobiotic studies is the retention of leaf organs on plants, the relative quantity of pollen grains produced by different fossil species or the significance of wildfire dynamics in ancient plant communities. Biostratinomy examination is a fundamental tool for elucidating fossil plant habitats. Numerous experimental data allow paleobotanists for evaluating the role of transport in the origin of fossil assemblages. Autochthonous plant assemblages, which are characterised by the preservation of fossil rooting structures, are relatively rare in the nature. In consequence, the search for palaeoecological information from parautochthonous to allochthonous assemblages has been a priority in taphonomy. As a result, taphonomic models have been elaborated in well-known sedimentological contexts, such as small lacustrine deltas, which allow for the distinction between riparian or perideltaic plant remains. Lithospheric processes modify plant debris after burial. The differences in the degrees of transformations (or alterations) during the diagenesis provide for information about the original morphology and biochemical composition of the plant tissues, which are also paleoecologically useful. Thus, amber diagenesis modifies resin biochemistry into new molecules that are still informative from the chemotaxonomical point of view.     

La comparaison à un niveau de référence : un nouveau traitement statistique de données paléoécologiques

The successive levels of a section are compared independently with a reference level (referential) having well identified characters. The comparison is realized by means of a distance or dissimilarity index. The choice of the index as function of the nature of data is argued, as well as the choice of the referential. This new approach is applied to the study of two examples from liassic series of southern France. The treatment of micropaleontological or faciological datas reveals cycles that are coincident with 3rd order eustatic cycles.     

Découverte de charophytes de l’Albien dans la Formation Kebar (Tunisie centrale) : implications paléoécologiques et paléobiogéographiques

In Tunisia, in the platform domain, the Aptian-Albian transition is associated with a major stratigraphic gap not precisely dated, which is related to the subaerial exposure of the Aptian Orbata platform. Locally, in central Tunisia (Jebel Kebar), this gap is substituted by the sedimentary records of the Kebar Formation. This formation provided a rich association of fossil charophytes, formed by Atopochara trivolvis trivolvis, Clavator harrisii zavialensis and Sphaerochara verticillata which allows attributing it to the late Aptian–early Albian interval (most probably early Albian). In addition, a new variety, Sphaerochara verticillata var. kebariensis, is described. The charophyte assemblage shows significant biogeographic affinities with a coeval flora found in the Iberian Peninsula. The Kebar Formation was previously regarded as exclusively nonmarine, but the presence of the assemblage of charophytes and associated ostracods described rather indicates a fluctuation between margino-littoral (lagoonal) and continental environments.     

Synthèse des données archéologiques récentes sur le peuplement à l’Holocène de la réserve de faune de la Lopé, Gabon

This article summarizes the results of archaeological research led from 1995 to 1998 in the fauna reserve of Lopé (Gabon). The excavated sites were dated from the Upper Pleistocene to the Post-colonial period. It is the longest and the most complete archaeological sequence presently known in Central Africa. These results show evidence of human presence in the reserve for over 40?000 years and that this greatly contributed to the preservation of the ecotone landscape of Lopé. In addition, these results offer the first systematic analysis of the sites and the ceramic artefacts produced and used in the centre of Gabon during the last three millennia. Supported by chronological, linguistic and palaeoenvironmental data, these results allow us to refine the ceramic typology and to prove the antiquity of husbandry, agricultural practices and iron production in this part of Africa. Finally, they allow us to clarify the various phases of settlement in the reserve and to reveal an important historic phenomena in connection with the expansion of the bantu languages and/or the bantu speaking peoples, who populate a third of the African continent.     

Signification paléoécologique des assemblages de diatomées du Messinien dans le bassin de Melilla-Nador (Rif Nord-Oriental, Maroc)

In the Melilla-Nador basin, the diatomites represent one of the main sedimentary components of the Messinian together with reefal carbonate platforms. Two vertical sections were realised in the diatomitic levels from distal platform. Diatom assemblages are for the first time described in this basin. A total of 125 diatom species were determined: 73 centrics and 52 pennates. Significant diatom assemblages defined from the statistical analysis indicate ecological variations concerning diatomitic levels or parts of diatomitic levels. Using the data sets we propose paleoenvironmental models showing the complexity of the ecological interactions. This study point the permanence of opened marine environment, the impulse of cold waters from Atlantic origin, a general decrease in bathymetry in the Messinian marls-diatomitic series, the influence of the carbonate platform progradation and the occurrence of upwelling systems.     

Nouvelles données sur 'encéphalisation des Reptiles Squamates

New datas on the level of encephalization of Squamate Reptiles This study carried out on 32 species of Lizards, 15 species of Snakes and one Amphisbaenian, the measure of the brain-weight (Brw) and the body-weight (Bdw) of which leads to the determination of the a and k parameters of the SNEL'S formula: Brw =k– Bdw^α. In a first stage we are able to demonstrate with 9 species of Saurians and 2 species of Ophidians, each species being represented by a sample the size of which variing between 30 to 80, that the intrinsic variability of the brain gives a mean value of 6.4% (isoponderal variability) or 7.5% (isometric variability). The intraspecific α coefficients (allometric coefficients of growth or of size) remain between.383 and.500; the mean value of which, .43 will be considered as a characteristic of the order Squamata. The interspecific α. coefficient (filiation coefficient of BAUCHOT and PLATEL) given by the 32 species of Lizards is .669, quite close to those previously calculated from a sample of 23 species (.686). The former values of the indices of encephalization belonging to these 23 species are meanwhile different. Six Lacertidae, selected as referrence Saurians (α= 627) lead to new indices of encephalization, the value of which will not be henceforth altered by the addition of new species to our present sample of Saurians. The various adaptative peculiarities roughly expressed by these indices of encephalization will be shortly studied in detail by the way of the volumetric analysis of the nuclear components of the brain. Amongst the 15 Snakes, the discrimination of 3 Henophidians and 12 Caenophidians leads for the last ones to an a filiation coefficient of .664; the value found for the Henophidians (.750) must be considered with suspicion because it get from only 3 species. We find with Anguis, the Amphisbaenian, some Scincidae and all the Snakes a low level of encephalization linked to the legless condition, which masks perhaps another peculiarities related to the evolutive processus which leads from Lizards to Snakes. The analyses of the K/Bdw relationship leads to results which differ from those found by BAUCHOT with the Insectivores-Primates. Separately Saurians and Ophidians do not show any correlation between the coefficient of encephalization and the body-weight; in compensation the Squamata in a whole show characteristics which express a negative rate of encephalization.     

Recherches sur les microorganismes de type mycoplasme dans les cicadelles vectrices et dans les vegetaux atteints de jaunisses

Résumé La phyllodie du trèfle, le Stolbur C et le Stolbur SM ont été étudiés chez la cicadelle Euscelis plebejus, les plantes Trifolium repens, Cuscuta subinclusa, Datura stramonium et Solanum lycopersicum en microscopie électronique, sur coupes ultrafines et après purification des agents infectieux.Dans les différents hôtes infectés, on distingue des éléments de grande taille, de forme ovoïde, amiboïde ou allongée, des corpuscules très contrastés, isolés ou en chaînettes, de fins filaments et des élements dégénérescents.Chez les cicadelles, la dégénérescence de ces microorganismes est probablement due à une réaction immunologique qui expliquerait la perte régulière du pouvoir infectieux de ces vecteurs.Chez les plantes, cette dégénérescence peut en partie rendre compte des phénomènes de rétablissements définitifs ou temporaires que manifestent parfois certains végétaux atteints de ces maladies.

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Summary The microorganisms causing the diseases Clover phyllody, Stolbur C and Stolbur SM were studied in the leafhopper Euscelis plebejus, and in the plants Trifolium repens, Cuscuta subinclusa, Datura stramonium and Solanum lycopersicum, by electron microscope examination of ultrathin sections and purified suspensions.In infected host plants and insects the following components were distinguished: large, ovoid, amoeboid or elongated bodies, well-contrasted isolated or chained microbodies, minute filaments, and degenerate elements. Some of these bodies resemble mycoplasma.In the leafhoppers it is possible that the degeneration of these mycoplasma-like microorganisms is due to an immunological reaction, which may explain why aged vectors do not transmit the diseases.In plants, the degeneration of the microorganisms was also observed. This loss may partly account for the occasional complete, or temporary, recovery of diseased plants.

     

Ressources complémentaires et mobilité dans le Magdalénien cantabrique. Nouvelles données sur les mammifères marins, les crustacés, les mollusques et les roches organogènes de la Grotte de Las Caldas (Asturies, Espagne)

Some animal and mineral resources, rarely identified in the levels of the Cantabrian Magdalenian, were exploited by the Paleolithic populations of the Nalón Valley (western Asturias) at the end of the Pleistocene. In this research, we present some of them, preserved in the Las Caldas Cave: dental remains and representations of marine mammals, marine crustaceans and molluscs, and diverse remains of amber and jet. These were selected, collected in ecosystems far away from the cave and, finally, transformed by the groups. These remains seem to complement the common resources exploited in Magdalenian paleoeconomy (e.g., ungulates, birds, fish, small carnivores, vegetables, flint, quartzite, quartz) recovered and exploited biotopes closest to the site. Our aim is thus to confirm a certain mobility of these communities towards the specific sources of raw material in search of subsistence resources potentially used in the activities of these communities (e.g., food, technology, social and symbolic expression, exchange).     

Isotopes stables (C,N) du collagène des mammouths de Mezhyrich (Epigravettien,Ukraine) : implications paléoécologiques

The mammoth steppe ecosystem was characterized by a high diversity in large mammals species distributed on a vast geographical range. The isotopic analyses of the collagen of the faunal remains from this context testified the niche partitioning among large herbivores with a specialization in the types of consumed plants. In the case of the mammoth (Mammuthus primigenius), systematic higher abundances in ¹⁵N are found for this species compared to those of other grazers in Eurasia and Alaska during the Upper Palaeolithic. This distinct isotopic signature reflects a specific ecological niche. The analyses of mammoth remains at the Epigravettian site of Mezhyrich (15,000–14,300 conv BP) reveal low abundances in ¹⁵N that are equivalent to those of the associated horses. Thus, the mammoth of Mezhyrich experienced a significant change in their environment and diet that probably led to the loss of their ecological niche. A likely direct competition with other large herbivores and the possible predation by wolves and human populations should be considered for the mammoth of the Ukrainian plains, long before their extirpation from the region.     

Le rôle de l'olfaction dans l'attraction exercée par les pousses et les fruits de pêcher sur les larves néonées de tordeuse orientale Cydia molesta

Summary The behaviour of newly hatched Cydia molesta larvae was studied in Petri dishes, at 23°C, in darkness. The trials of varying duration, each consisted of 50 larvae (ten replicates of five larvae). The larvae were strongly attracted by either a recently cut piece of growing peach twig or a piece of a fresh peach skin. These were clearly preferred to equivalent wet papers. One hundred percent relative humidity was provided by covering the bottom of the dishes with wet paper. The proportion of larval attracted by the plant material reached or exceeded 84% inside 50–60 minutes.In other trials, the larvae were also attracted by concentrated extracts of peach twigs and fruits prepared with chloroform. The bottom of the dishes was covered with dry paper and the larvae continually observed with a video camera under a dim red light (10 lux). The extracts from growing peach twigs were more attractive than those of fruits and physiologically old twigs.The role of olfaction in the behaviour of larvae and the diffusion of semio-chemicals by the plant are demonstrated.

     

Données paléoenvironnementales sur le Vraconnien/Cénomanien de la région de Tébessa (Atlas Saharien,nord-est Algérie). Caractérisation de l’OAE2

The micropalaeontological content of five sections, located in Northeastern Algeria (Saharan Atlas) was investigated by means of washing/counting of microfossils in marly levels, and microfacies analyses of calcareous levels. In these levels of Upper Cretaceous age, hundred species of foraminifera were identified but only about 15 species of ostracoda and about ten of radiolaria. This work allows, first of all, to establish a rather precise stratigraphic frame, in particular by means of studying planktonic foraminifera. Two to five biozones were defined, between the Vraconnian (Th. Appenninica biozone) and the early Turonian (Whiteinella archaeocretacea biozone, then Helvetoglobotruncana Helvetica biozone for certain sections). Secondly, the quantitative analyses led on foraminifera allowed the definition of palaeoenvironment. The ratio P/P+B, generally very high, coupled with a little diversified benthonic microfauna, indicates a calm and deep environment, of external platform or slope type. Furthermore, at numerous levels, various indications give evidence of the existence of a strong surface productivity (presence of upwellings), responsible for the proliferation of radiolaria (late Vraconnian/early Cenomanian especially) or of globular planktonic foraminifera (hedbergellids/heterohelicids); being both associated with low-oxygen deep waters. Two anoxic events were also revealed, the first one at the end of Vraconnian (OAE1d) and the second at the end of Cenomanian (OAE2). This last event in particular was characterized on all the sections, in a more or less detailed way, thanks to the identification of certain indicator: Heterohelix “bloom”, “filament” event, disappearance of rotaliporids, presence of “blackshales” strongly enriched in organic matter (Bahloul levels).     

Effet de l'enrichissement continu en nitrates sur les populations de Diatomées isolées à l'aide d'enceintes expérimentales placées dans un étang oligotrophe

The influence of nitrates (NH₄NO₃ KNO₃ and Ca(NO₃₎₂) on Diatom populations has been studied. These populations were isolated by enclosures with transparent walls, without bottom or lid, placed in an oligotrophic pond. The addition of NH₄NO₃ generally resulted in a decrease in the number of Diatoms and the disappearance of some species. The addition of KNO₃ and Ca(NO₃₎₂ was followed, during some periods, by a very important increase of Achnanthes minutissima, Fragilaria construens and Gomphonema parvulum.     

Les récentes découvertes à Baerya dans le district de Bijie, au nord de la province de Guizhou (Chine)

Fauna associated with stone artifacts have recently been uncovered, in the course of a survey from a cave site named Baerya, town land of Bijie, Guizhou province. The first observations suggest a human occupation. In the absence of chrono-stratigraphic data, it is not possible to assess the age of the site. Nevertheless the presence of lower Pleistocene fauna suggests a very ancient age for this human occupation. Further field research will be necessary to determinate the age and nature of the site.     

Influence de la 6-benzylaminopurine sur la différenciation plastidiale dans les cotylédons de concombre

Treatment with 6-benzylaminopurine (6-BAP; 10⁻⁵ g/ml) accelerates the growth of detached cucumber cotyledons (Cucumis sativas L.), primarily through an increased water uptake by the tissues. A comparative study of pigment composition and ultrastructure in 6-BAP treated and untreated cotyledons shows that cytokinin, in the presence of light, accelerates the transformation of etioplasts into chloroplasts. 6-BAP also enhances the synthesis of membrane precursors as indicated by the formation of a dense prolamellar body and by the persistence of a pseudo-cristalline structure in 6-BAP treated material. Stimulation of biosynthetic activity by cytokinin leads simultaneously to an increase in the rate of the pigment synthesis and to an acceleration in the building of the lamellar system. Furthermore, chloroplasts of 6-BAP treated cotyledons show abnormal features such as a striking increase in the number of thylacoids per granum and a poor development of the intergranal system.     

Stratigraphie, paléoécologie et foraminifères du paléogène des Alpes Maritimes et des Alpes de Haute-Provence (Sud-Est de la France)

Paleogene sedimentation in the Alpes Maritimes and Alpes de Haute Provence regions is composed of one complete sedimentary sequence. This sequence begins with the continental Formation from Microcodium and continues with the Cerithium layers, the Calcaires Nummulitiques and the Marnes Bleues, which are overlaid by the turbidites of the Grès d’Annot Formation. Sedimentation starts in the Nummulites perforatus zone close to the base of ‘the Truncorotaloides rohri zone (P 14) and ends in the Cassigerinella chipolensis-Pseudohastigerina micra zone (P 18) and the NP21 zone in the upper part of the Grès d’Annot. More biomarkers were used in order to define a more detailed local biozonation (biozones AMP 1 to AMP 7). Four local zones were also defined by the last occurrence of Nummulites millecaput and N. perforatus-N. ptukhiani and then by the first appearance of N. retiatus (AMGF 1-4). The evolution of benthic foraminiferal assemblages shows an increase in bathymetry from the internal platform in the Cerithium layers to the calcareous platform with large foraminifers, then to the external platform and the deep offshore environment of the Marnes Bleues and Grès d’Annot. Low faunal diversity in the Grès d’Annot together with the predominance of agglutinated species indicates a poorly oxygenated, organic rich and turbidite environment. Seven steps (SD 1 to SD 7) in the Eocene marine transgression are shown from East to West by detailed local biozonation and sequence analysis. Grès d’Annot sedimentation is also diachronous, beginning within the Truncorotaloides rohri zone (P 14, AMP 1) in the East and ending within the Pararotalia opima opima zone (P 20, middle Rupelian) in the West (Barrême). Small foraminifer Paleogene fauna from the Alpes Maritimes and Alpes de Haute Provence was studied from 400 samples. It is composed of 378 species. Two new taxa are proposed: Fissurina niceana n. sp. and Globocassidulina alpina n. sp. The species from the Escarène and Gorbio neighborhood described by M. von Hantken (1884) were re-examined.