Les ostracodes plio-pléistocènes de la côte orientale de la Péninsule du Cap Bon (Tunisie)

This article concerns the study of the ostracods of the Upper Pliocene-Lower Pleistocene sedimentary deposits cropping out along the south-eastern coast of the Cape Bon Peninsula (Tunisia, Hammamet region, Sidi Khelas section). Fourteen samples were taken along a thirty-two-meters thick sedimentary silico-clastic series. Seventy species of ostracods belonging to twenty-four genera were found. The autochthonous association, which originally lived in an environment located in the infralittoral and upper circalittoral stages of the benthic marine domain, is cyclically affected by inputs from the more superficial environments due to the presence of relatively well-developed lagoon and/or estuary environments in the surrounding coastal areas. Within the ostracod association, the presence of Bythocythere turgida – a true “northern guest” – is particularly significant. This species indicates that these sediments were deposited during the cold phases of the Early Pleistocene. Among the ostracods found, those belonging to the families Trachyleberididae, Hemicytheridae and Bythocytheridae, which are dominant and include particularly significant species from the environmental and paleoclimatic point of view, are systematically recorded and commented on. Some species that are probably new have been described and photographed, but are currently left in open nomenclature because of how few specimens have been found.     

Les ostracodes et foraminifères associés des dépôts de l’Éocène moyen et supérieur de la coupe de Jebel Serj (Tunisie centrale). Intérêt biostratigraphique,paléoécologique et paléobiogéographique

The ostracod fauna collected from the Cherahil formation that crops out at the Jebel Serj section (central Tunisia) contains 24 species belonging to 12 genera. These ostracods are associated with 9 genera of benthic Foraminifera (including 4 Nummulites species) and 7 genera of planktonic Foraminifera. The biostratigraphic study of ostracod assemblages results to the recognition of 6 biozones which are correlated with Lutetian-Priabonian. The Shannon Weaver, Margalef and equitability indices point to internal platform netritic conditions, with minor fluctuations in depth and oxygenation. The palaeobiogeographic distribution of ostracod species found in the study area of Central of Tunisia establishes a good connexion with the basins developed in Northern Africa (Tunisia, Algeria, Libya and Mauritania) and the Middle East (Egypt and Jordan).     

L'origine et l'évolution du xylème chez les Trachéophytes

Abstract

Xylem origin and evolution in the Tracheophyta. - The research on the xylem origin and evolution leads to investigate three features - guides:

—Passage from homoxyly to heteroxyly.

—Reduction of the importance of primary centripetal xylem in geological time.

—Progressive decrease of initial cambial cells lenght in the main groups of plants.

In this connection, one should recall the phloem-xylem evolution laws instituted by Chauveaud (1931).

From this well defined estimations on fossil vascular plants with secondary xylem, a clear evaluation of phylogenic significance of wood pattern by means of correlation with a wide range of various anatomical features is reached.

Salient evolutionnary trends of secondary xylem are illustrated with significative pattern examples related more particulary to fossil homoxylous structures of Sphenophyta, Gymnosperms and homoxylous or heteroxylous Dicotyledons.

Furthermore, unusual and rare structure of Pentoxylales and Rhexoxylales, particularly with regard to the cambium functionning must be recalled.     

Signification paléoécologique et paléogéographique des bivalves du Carbonifère inférieur du bassin d’Ancenis (Massif armoricain)

Palaeoecological and palaeogeographical inferences from Early Carboniferous bivalves of the Ancenis Basin (Variscan belt, France). In the basal part of the Ancenis Formation, of Dinantian age, greenish to purple mudstones display a few bivalves, assigned to the genera Lithophaga, Modiolus, and Naiadites. Because Naiadites is considered to be a non-marine bivalve, and is only previously reported in Scotland in Dinantian rocks, a brackish environment can be assumed for the Ancenis Basin during the Early Carboniferous. To cite this article: M. Ballèvre, H. Lardeux, C. R. Palevol 4 (2005).     

Interprétation paléogéographique des données palynologiques du site du Paléolithique supérieur de Mezhyrich (Ukraine)

The results of palynological study of the Upper Paleolithic Mezhyrich site in central Ukraine are presented. Four local pollen zones were identified. The results of the palynological investigations allow us to hypothesize that the plant cover during Upper Paleolithic had a mosaic structure. The pollen record shows the presence of a few tree species with the predominance of herbaceous plants. We suggest that the river valleys and other local favorable sites were natural refugia where forest elements could survive even during the Last Glacial Maximum. These favorable landscapes to the existence of prehistoric hunters may have persisted during the Last Pleniglacial.     

Les premiers vertébrés et les premières étapes de l’évolution du crâne

The earliest vertebrates and the first steps of the evolution of the skull. Vertebrates are one of the few metazoan taxa, which display a well-corroborated phylogenetic pattern, a good and anatomically informative fossil record, and a relatively slow ontogenetic development. They are thus a favourite taxon for illustrating evolution as a historical process, although the stem of the vertebrate tree remains poorly documented by fossils, except for some Early Cambrian forms. Therefore, the characterization of the vertebrates now rests essentially on a small number of developmental characters, mostly involved in the rise of the skull, and whose precursors may occur in other chordates. The tree of the crown-group vertebrates also shows some major morphological gaps due to early extinctions, but a number of Palaeozoic stem gnathostome taxa helps in documenting the agnathan-gnathostome evolutionary transition. However, stem cyclostomes remain elusive.     

Nouvelles données paléontologiques,paléoécologiques et sédimentologiques sur le Berriasien de la région de Lamoricière (ouled Mimoun et E1 Rhoraf,Monts de Tlemcen,Algérie)

In the Western Algerian area, the Ouled Mimoun and El Rhoraf sections are particularly appropriate for the study concerning the berriasian formations.From tha lithostratigraphical point of view, the upper section of the carbonated platform corresponds to the lower Berriasian and a part of the middle Berriasian. The «Argiles de Lamoricière which dominate it belong to the middle and upper Berriasian. The subjacent detritic formation known as «Grès de Berthelot probably begins with the lower Valanginian. The stratigraphical results are based on an abundant fauna (ammonites, ostracods) collected in situ, the main species of which have been the subject of a paleontological review and abondantly illustrated.The studied series offer a good example of the evolution of sedimentary conditions which accompany the temporary opening of a carbonated platform towards the open sea.The variations in fauna composition are closely related to changes in environment. In particular, the presence of ammonites in the Boissieri zone can be connected to the highest point of marine advance, although the depth remained relatively shallow (an upper infratidal zone being likely). It is to note that during this period the low level of sedimentary activity favored the settling of some remarkable epilithic fauna.Above the «Argiles de Lamoricière, the massive detritic sedimentation (grès de Berthelot) could indicate an important paleogeographical change in the interior. In the area studied, the ostracods encountered in the basal section of the last formation still mean a shallow marine environment.     

Contribution à la stratigraphie du site paléolithique de Mezhyrich (Ukraine)

This paper deals with a geoarchaeological study developed at the Epigravettian settlement of Mezhyrich (Ukraine) in the frame of the French ANR project “Mammouths”. Based on a microstratigraphic analysis of a complex loess sequence, this approach has provided a large set of complementary data focusing on archaeology, environment and chronology, which document the activities of the Epigravettian hunters at the site between ca 18,300 and 17,400 before present, during a cold period characterized by strong climatic and environmental contrast.     

L'évolution des gastéropodes lacustres et la paléoéologie des diatomées dans le Néogène de Kos (Dodécanèse,Grèce)

Evolutionary lineages of several limnic gastropod genera (Viviparus, Melanopsis, Theodoxus) from the Neogene of Kos island (Dodecanese, Greece) are described and interpreted. The attempt is made to analyse the paleoecological development of a limnic sedimentary basin in the eastern portion of Kos by means of Diatoms. Obviously, there is no relation between the chemical parameters of the water of the former lake and the morphological development of the gastropods. The lineages of Viviparus brevis, Theodoxus doricus and Melanopsis gorceixi are suggested to be caused by phyletic transformations and not by changing environmental conditions. It is, thus, possible to establish a local biostratigraphy based on subspecies, and moreover, a more regional one based on longer ranging species.     

Etude cytochimique et ultrastructurale de l'évolution ovocytaire de Nereis pelagica L. (Annélide Polychète)

Résumé Les ovocytes de N. pelagica d'un diamètre inférieur à 100 ne renferment dans leur cytoplasme que des inclusions lipidiques et vitellines. Les lobules vitellins s'accroissent par l'adjonction de vésicules golgiennes.L'approche de la maturité sexuelle est caractérisée par l'apparition de mucopolysaccharides acides. Corrélativement à l'élaboration de ce matériel, l'appareil de Golgi présente, à ce stade, de profondes modifications morphologiques: dilatation des saccules distaux et libération dans le cytoplasme de vacuoles golgiennes. Les processus de vitellogenèse cependant ne sont pas entièrement stoppés.Dans les ovocytes matures, les lobules mucopolysaccharidiques forment une gangue corticale. Les dictyosomes sont refoulés vers l'intérieur du cytoplasme et présentent des figures d'involution.La présence de lamelles annelées intra-nucléaires a été observée de façon constante dans tous les ovocytes matures examinés.

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Cytochemical and ultrastructural study of oocyte development in Nereis pelagica L.I. Normal ovogenesis

Summary The oocytes of N. pelagica, the diameter of which is smaller than 100 , contains only lipid and yolk inclusions in their cytoplasm. The yolk bodies grow by confluence of Golgi vesicles.The advent of the sexual maturity is marked by the appearance of acid mucopolysaccharides. Concomitantly with the production of this material, the Golgi apparatus shows typical morphological modifications: dilatation of the distal saccules and release of Golgi vacuoles into the cytoplasm. However vitellogenesis is not completely terminated at this point.In the mature oocytes the mucopolysaccharid material forms a cortical layer. The dictyosomes are pushed toward the center of the cytoplasm and show signs of degeneration.The presence of intranuclear annulate lamellae is a constant feature in all mature oocytes examined.

     

Flore du Jurassique basal de la ville de Mende (Lozère) : synthèse des gisements historiques,nouvelles données sédimentologiques,paléontologiques et paléoenvironnementales

During the 20th century, because of urbanization, most palaeontological sites yielding plants (Hettangian–Sinemurian in age) from the city of Mende have disappeared, or they have been forgotten. This article presents a synthesis of sites yielding plants, from their discoveries in the 19th century to recent prospecting. New lithostratigraphic and palaeobotanical data are brought for two historic sites (Ravin del Pouset and Petit Séminaire), as well as two new localities (Causse d’Auge road and Gardès road). This study reveals the diversity of plant-containing lithofacies (dolomudstone, marl, limestone/calcarenite and oo-bioclastic limestone) and the diversity of plant preservations (charcoalified compressions with or without cuticle, isolated cuticle, external casts/impressions). Microfaciological study of plant beds demonstrates the diversity of depositional environments. Protected, restricted and shallow environments with low wave exposure and probable euryhaline conditions are clearly the most favourable to the accumulation and the preservation of fossil plants. These early Liassic palaeofloras, among the southernmost yet reported for Laurasia, are of significance for the plant geography and global paleoecology at that time.     

Fonctions histoenzymatiques lors de l'évolution et de la lutéolyse du corps jaune de la lapine

Résumé Trente cinq enzymes sont recherchées lors de l'étude comparative de la lutéinisation et la lutéolyse. Vingt six sont histochimiquement décelables dans les corps jaunes gestatifs leur permettant de stocker et métaboliser glucides, corps gras, nucléotides, amines, phosphates, sulfates et d'autres métabolites. Les activités importantes des enzymes de la voie des pentoses, des diaphorases et de la stéroïde 3 ol DH témoigneraient d'une stéroïdogenèse active. Les cellules lutéiniques thécales semblent histoenzymatiquement mieux pourvues au début de la luteinisation; les cellules lutéiniques granuleuses le sont pendant les stades ultérieurs.La lutéolyse est marquée par une diminution de la plupart des activités enzymatiques. Les activités tant qu'elles existent, sont topographiquement limitées (ilôts actifs extra lutéaux) et surtout métaboliquement restreintes. L'équipement enzymatique des structures lutéales très involuées suggère plutôt qu'une stéroïdogenèse même résiduelle des processus typiques et une activité des éléments conjonctifs (fibrillogenèse).

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Histoenzymatic functions of the evolution and the luteolysis of the corpus luteum of the rabbit

Summary 35 enzymes were investigated in the course of a comparative study on the luteinisation and luteolysis. 26 of them were found in the corpora lutea during gestation. They were able as a consequence to stock and the metabolize glucides, lipides, nucleotides, amines, phosphates, sulphates as well as other metabolites. The strong activities of the pentose shunt's enzymes, of the tetrazolium reductases and ⁵ 3 OH-steroide DH indicated most probably an active steroidogenesis. The theca-luteinic cells appeared having a stronger histoenzymatic activity in the beginning of the luteinisation; the granuloso-luteinic cells showed a stronger activity in the later stades.The luteolysis is characterized by a decrease of the activity of the preponderant number of the enzymes mainly in the degenerated luteal cells. The enzymes activities as far as such existed were topographically limited (active extraluteal islands) and restricted mainly in their metabolizing possibilities. The author's results suggested as more probable the existence of a process of lysis and an activity of the connective tissue elements (fibrillogenesis) than a steroidogenesis, even though in a residual or terminal form.

     

Figures sédimentaireset traces d'origine biologique du Trias moyen de la bordure orientale du Massif Central signification sédimentologique et paléoécologique

The sandstones with foot-prints of reptiles and saltcasts from the Middle Triassic of the eastern border of the Massif Central (France) show a striking reptilian ichnofauna. The numerous sedimentary figures and trace fossils which are described here allow to deduce the following characteristics of the depositional environment: shallow water, lower flow regime, periodical increase of salinity. The reptiles used to pass through that environment where numerous stretches of water alternated with emerged, plant overgrown areas.     

Faunes d'oiseaux du pléistocène de France: Systématique, évolution et adaptation,interprétation paléoclimatique

Statistical comparison between bird populations from Lower and Middle Pleistocene and present ones makes it possible to demonstrate evolutionnary shifts such as increase in size or, on the contrary, decrease in size in some lineages and to discover some species or subspecies already found in Central Europe, in layers of the same epoch. In some other lineages the observed variations seem to be regarded as possible adaptations to local geographical conditions.Moreover the study of the birds contributes richly to the reconstitution of climates and biotops. The percentage variations of «cold birds in a given site makes it possible to confirm climatic fluctuations already discovered by other methods of study.     

Les formations de la limite Jurassique-Crétacé en Tunisie septentrionale (Djebel Oust). Série lithologique; résultats biostratigraphiques et paléogéographiques d'après les Ammonites,les Calpionelles et les Ostracodes

A stratigraphic research concerning Tithonic-Berriasian beds in northern Tunisia (Djebel Oust) points out that here, as in some parts of Algeria, the Inferior Cretaceous detritic phase begins in the Berriasian. A gradually deepening of the sea is noted from Inferior Tithonic till Middle Berriasian, with bathyal to hemipelagic facies, and submarine slidings. There are close similarities in ostracodal associations with Monts de Batna in Algeria, and some affinities are observed with the central Apennines in Italy.     

Les Pachyerymnoceras (Pachyceratidés,Périsphinctacés,Ammonites) du Callovien moyen et supérieur de la région de Saida (Algérie occidentale). Origine phylétique et biogéographie des Pachyceratidés

The genus Pachyerymnoceras, with four new species,is described for the first time in Western Algeria. The genus first appears in the Middle Callovia (Coronatum Zone) as in Saudi Arabia. It is represented in the Saida region by uncommon P. praecox nov. sp. followed during the Upper Callovian (Athleta Zone) by specimens belonging to P. flamandi sp. nov., P. kmerense nov. sp. and P. saidense nov. sp. Every species is represented by a dimorphic pair.Pachyceratidae are put into Perisphinctaceae. If Pachyerymnoceras arises from Erymnoceras, a genus suddenly appearing during the Middle Callovian on northern and southern Tethyan borders, the origin of Erymnoceras is still unknown. Three phylogenetic hypothesis are considered here. Erymnoceras may have evolved during Lower Callovian: 1) from serpenticonic Tethyan Pseudoperisphinctinae like Choffatia (Subgrossouvria); 2) from Tulitids via ellipticoncic Bullatimorphites (Kheraiceras); 3) through a double lineage arisen in Subboreal and Tethyan platyconic Proplanulitids.Pachyceratids have a wide paleobiogeographic distribution in NW Europe and on the Tethyan margins. The genus Pachyerymnoceras evolves in Ethiopian Province of the Tethyan Realm. Some species migrate into Indo-Malagasian Province and others, through the south Tethyan border came to Europe were they are found restricted to Upper Callovian (Athleta and Lamberti Zones). Therefore this migration has a duration of two or even three zones.