Structure of a corystosperm fossil forest from the Late Triassic of Argentina

A palaeoecological study of a standing Late Triassic forest containing 150 silicified stumps from the Río Blanco Formation of Mendoza province, Argentina is described. A mapped portion of the forest floor provides quantitative data — tree density, mean separation of trees and basal area per stump — which, along with taxonomic and sedimentologic information, allowed the reconstruction of a plant community that grew along river banks and within proximal floodplain environments. Analysis of architectural and phenological data from monotypic forest indicates an evergreen community composed of a corystosperm genus with a canopy height of c. 13–21 m. The corystosperm taxon: Elchaxylon, like Rhexoxylon, has polyxylic axes with centripetal secondary xylem but does not generate perimedullar bundles and the centrifugal secondary xylem produces an undivided solid pycnoxylic cylinder. Vegetation analysis shows that the forest has a clustered distribution pattern with high density. Forest density ranges between 727 and 1504 trees/ha but there are first order clusters with elevated density (mean nearest neighbour distance of 1.85 m). The histogram of diameter classes based on 131 stumps suggests an earlier colonization by few older pioneers (the largest ones) followed by establishment of a large younger cohort of coeval trees. Based on 9 series and 139 rings, the mean ring width and mean sensitivity (MS) were 3.47 mm and 0.31 respectively. MS values and the presence of false rings indicate the forest community responded to stressed ecosystems. The growth rings are very erratic and range from 0.27 to 8.94 mm. For fossil growth analysis it was assumed that wider rings would suggest a warmer climate and the considerable range in growth rates would indicate variability in the limiting factors among subsequent cycles.     

Composition of the walls of pollen grains of the seagrass Amphibolis antarctica

The composition of walls isolated from pollen grains of the seagrass Amphibolis antarctica was determined. Glucose, galactose, and rhamnose were the major neutral monosaccharides in the wall polysaccharides, and fucose, arabinose, xylose, and mannose were present in minor proportions. No apiose, a monosaccharide present in the wall polysaccharides of the vegetative parts of the seagrass Heterozostera tasmanica, was found. Large amounts of uronic acid (mainly as galacturonic acid) were found in the walls. The monosaccharides were probably present in cellulose and pectic polysaccharides, the latter comprising neutral pectic galactans, and rhamnogalacturonans containing high proportions of rhamnose. The walls contained a small amount of protein; glycine and lysine were the amino acids present in the highest proportions. Histochemical examination of isolated walls confirmed the presence of polyanionic components (pectic polysaccharides), -glucans (cellulose), and protein. The composition of the walls is discussed in relation to analyses of the walls of pollen grains and vegetative organs of other plants.     

Melissiotheca: a new pteridosperm pollen organ from the Lower Carboniferous of Scotland

Melissiotheca is based on fusainized pollen organs of pteridospermous affinities which occur abundantly in an Upper Visean limestone at Kingswood, near Pettycur (Scotland). The new species is a pedicellate synangium composed of 50–150 sporangia each of which is embedded at its base in a parenchymatous cushion divided into lobes. The sporangia are fused along their proximal half but are free distally. Dehiscence is longitudinal. Each sporangium is supplied at its base by a single vascular strand. Prepollen is small, spherical and trilete with a rugulate exine. In ultrastructure, the nexine appears homogeneous; the sexine shows internal sculpture of granae and rod elements. Melissiotheca has not been assigned to any family, but it shows many affinities with pollen organs attributed to the Lyginopteridaceae.     

Melissiotheca: a new pteridosperm pollen organ from the Lower Carboniferous of Scotland

Melissiotheca is based on fusainized pollen organs of pteridospermous affinities which occur abundantly in an Upper Visean limestone at Kingswood, near Pettycur (Scotland). The new species is a pedicellate synangium composed of 50–150 sporangia each of which is embedded at its base in a parenchymatous cushion divided into lobes. The sporangia are fused along their proximal half but are free distally. Dehiscence is longitudinal. Each sporangium is supplied at its base by a single vascular strand. Prepollen is small, spherical and trilete with a rugulate exine. In ultrastructure, the nexine appears homogeneous; the sexine shows internal sculpture of granae and rod elements. Melissiotheca has not been assigned to any family, but it shows many affinities with pollen organs attributed to the Lyginopteridaceae.     

Apiosordaria antarctica and Thielavia antarctica, two new ascomycetes from Antarctica

Two new species of ascomycetes, Apiosordaria antarctica, isolated from soil, and Thielavia antarctica, isolated from a sample of the lichen Usnea cf. aurantio-atra, both collected on King George Island (Antarctica), are described and illustrated. Apiosordaria antarctica is characterized by ostiolate ascomata with agglutinated hairs, eight-spored, uniseriate and cylindrical asci, and two-celled, irregularly navicular ascospores, with an upper cell ornamented with very small warts and with an apical germ pore. Thielavia antarctica is characterized by nonostiolate ascomata, with a thick peridium, eight-spored, cylindrical asci, uniseriate, oblate, ovoid ascospores, a slightly protruding apical germ pore, and a phialidic anamorph.     

The oldest nautiloid recorded from the Triassic Germanic Basin and the first ammonoid from the Aegean (Middle Triassic) of Poland

During the Triassic in Europe, the Germanic Basin extended from England in the west to the eastern border of Poland in the east. Although cephalopods are common in some Middle Triassic (Muschelkalk) horizons, there still persists a gap in the palaeontological record of the eastern part of the Germanic Basin, notably in the lowermost parts of the Lower Muschelkalk, spanning the latest Olenekian-Aegean interval. The present contribution attempts to fill this gap by presenting the first ammonoid (ceratitid Beneckeia sp.) and nautiloids (Germanonautilus cf. dolomiticus and G. cf. salinarius) from the Lower Gogolin Beds (Upper Silesia, Poland). These Germanonautilus are the oldest nautiloids found in the entire Germanic Basin.     

The temnospondyl amphibian Cyclotosaurus from the Upper Triassic of Poland

Abstract:  A gap in the Late Triassic fossil record of the capitosaur amphibian Cyclotosaurus is filled by new material from lacustrine deposits at Krasiejów, Poland, corresponding in age to the Lehrberg Beds (late Carnian) of Germany. The skull of the Polish cyclotosaur is intermediate in several respects between that of Cyclotosaurus robustus from the middle Carnian Schilfsandstein of Germany and the younger C. mordax from the early Norian Stubensandstein. It shows a decrease in the width of the skull and in the degree of concavity of the posterior margin of the skull roof. The differences are significant enough to warrant erection of a novel species, the name Cyclotosaurus intermedius sp. nov. being proposed. The pectoral girdle, identified for the first time in Cyclotosaurus , suggests the genus was more fully adapted to an aquatic mode of life than was Paracyclotosaurus .     

The marine diapsid reptile Endennasaurus from the Upper Triassic of Italy

Abstract:  The marine reptile Endennasaurus from the Upper Triassic Zorzino Limestone of northern Italy is redescribed and reassessed. New details of the skull and postcranial skeleton are revealed, confirming the attribution of this genus to the diapsid reptile clade Thalattosauriformes. Phylogenetic analysis suggests that Endennasaurus was related to the European genus Askeptosaurus and the Chinese Anshunsaurus . Despite a rather conservative postcranial morphology, Endennasaurus clearly occupied a highly specialized dietary niche as it combined a slender tapering premaxillary rostrum with a complete absence of either marginal or palatal teeth.     

The role of iron in the bacterial degradation of organic matter derived from Phaeocystis antarctica

In high-nutrient low-chlorophyll areas, bacterial degradation of organic matter may be iron-limited. The response of heterotrophic bacteria to Fe addition may be directly controlled by Fe availability and/or indirectly controlled through the effect of enhanced phytoplankton productivity and the subsequent supply of organic matter suitable for bacteria. In the present study, the role of Fe on bacterial carbon degradation was investigated through regrowth experiments by monitoring bacterial response to organic substrates derived from Phaeocystis antarctica cultures set up in <1 nM Fe (LFe) and in Fe-amended (HFe) Antarctic seawater. Results showed an impact of Fe addition on the morphotype dominance (colonies vs. single cells) of P. antarctica and on the quality of Phaeocystis-derived organic matter. Fe addition leaded to a decrease of C/N ratio of Phaeocystis material. The bacterial community composition was modified as observed from denaturing gradient gel electrophoresis (DGGE) profiles in LFe as compared to HFe bioassays. The percentage of active bacteria as well as their specific metabolic activities (ectoenzymatic hydrolysis, growth rates and bacterial growth efficiency) were enhanced in HFe bioassays. As a consequence, the lability of Phaeocystis-derived organic matter was altered, i.e., after seven days more than 90% was degraded in HFe and only 9% (dissolved) and 55% (total) organic carbon were degraded in LFe bioassays. By inducing increased bacterial degradation and preventing the accumulation of dissolved organic carbon, the positive effect of Fe supply on the carbon biological pump may partly be counteracted.     

Reproduction in seagrasses: pollen wall morphogenesis in Amphibolis antarctica and wall structure in filiform grains

The pre–meiotic anther of the marine angiosperm Amphibolis antarctica contains microsporocytes and sterile cells. The microsporocytes divide conventionally to produce tetrads, but the sterile cells degenerate and contribute to the future pe–riplasmodium. Each tetrad of young microspores is contained within a vesicle defined by a membrane. After release from the tetrad, the microspores increase in length and rapidly become filiform. The microspore nucleus soon divides and partitioning of the cytoplasm delimits the generative cell from the vegetative cell of the binucleate pollen grain. The division and the early pollen growth occurs while the grains are segregated within vesicles in the periplasmodium. These compartments, established at microspore release, remain structurally intact throughout the vacuolate period of pollen development, when pollen wall assembly begins. This process is initiated as particles migrate from the inner face of the vesicle membrane into the lumen of the vesicle and microfibrillar elements form between adjacent particles. The particles and microfibrils form a loose, three–dimensional network. The vesicle membrane then disappears and the binuclate grains become immersed in the tapetal residuum. Additional wall components are now deposited upon the primary fibrillar stratum. Short lamellae, resembling fragments of membrane, frequently associated with electron–opaque globuli, are found intermixed with the surface microfibrils. Apparently, granular material originating in the degenerating periplasmodium may be the precursor of the globuli, and contact with the lamellae brings about an alteration in state. At this stage the pollen wall is resolved as two distinct fibrillar strata and the lamellae and globuli are incorporated as inclusions into the superficial zone of the outer stratum. The mature pollen wall exhibits faint stratification and the presence of the subsurface inclusions is readily demonstrated in germinating grains by section staining with phosphotungstic acid. The pollen wall in A. antarctica is compared with that in filiform grains of other seagrasses.     

Chlorophycean algae from the Triassic of Australia

Among living green algae assigned to the order Chlorococcales and order Zygnematales certain species develop resistant outer organic walls and/or cysts during their life cycles; as such they have the potential to become fossils. Based on morphology, comparison between living algae and microfossil remains are made with varying degrees of confidence, and a possible evolutionary pathway for certain chlorococcalean coenobial families is suggested. Twelve genera are reviewed from earliest to latest Triassic palynological assemblages from northwestern Australia; and the following taxa are described as new: Plaesiodictyon mosellanum ssp. symmetricum ssp. nov.; Plaesiodictyon mosellanum ssp. variabile ssp. nov.; Plaesiodictyon decussatus sp. nov.; Plaesiodictyon decussatus ssp. decussatus ssp. nov.; Plaesiodictyon decussatus ssp. tetracornuta ssp. nov.; Tetraporina protrusa sp. nov.; Crucigeniella? torques sp. nov.; and Paleoraphidia akestra gen. et sp. nov. (type). Their suggested natural affinities are useful in palaeoenvironmental interpretations of mostly freshwater or low-salinity habitats.     

The mixosaurid ichthyosaur Contectopalatus from the Middle Triassic of the German Basin

The skull of the mixosaurid species Contectopalatus atavus (Quenstedt, 1851-52) is the most bizarre of any known ichthyosaur. It possesses a very high sagittal crest formed by the nasal, frontal and parietal bones which grows higher during ontogeny. This skull structure - found to a lesser extent in the other mixosaurid genera Mixosaurus and Phalarodon - is a synapomorphy of the family Mixosauridae. It is here interpreted as correlated with a unique arrangement of the jaw adductor musculature among tetrapods, with the internal jaw adductors extending over most of the skull roof up to the external narial opening. This reconstruction would increase the biting force considerably and the hypothesis is supported by peculiarities of the dentition and jaws of Contectopalatus. Contectopalatus probably reached a length of about 5 meters. It is therefore the largest known mixosaurid and one of the largest Triassic ichthyosaurs. The general text-book picture of mixosaurs as small, rather unspecialized, primitive ichthyosaurs is incorrect. Mixosaurs were a highly specialized, uniquely adapted and very diverse ichthyosaur family, some members of which rank among the marine top predators of their time.     

The oldest Mesozoic nearshore Zoophycos: evidence from the German Triassic

The trace fossil Zoophycos has been described from the Middle Triassic carbonates of the German Basin for the first time. It occurs in a calcilutite bed at the top of a shallowing-upward cycle (parasequence) in the transgressive systems tract of the Middle to Upper Muschelkalk sequence of Thuringia (Germany). Based on sedimentological and palaeontological features, the studied interval is interpreted as deposited in a marine nearshore environment with proximal storm deposits (tempestites). Zoophycos occurs in a very simple planar form with lobate spreiten, which were most likely produced by a worm-like animal by strip mining. The upper tier of the ichnofabric consists of Zoophycos, whereas the lower tier is occupied by cylindrical trace fossils of unknown taxonomic affiliation and with decreasing size towards the bottom. Associated trace fossils such as Rhizocorallium, Balanoglossites and Trypanites indicate a partly firm to hard substrate. No mixed layer is developed at the top of the trace fossil bearing succession. The ichnofabric together with the sedimentological features (disseminated pyrite, blue-grey colour) and palaeontological circumstances (poor benthic fauna, meiofauna with a small body size) support an interpretation of a dysaerobic environment. In the view of evolutionary change, Palaeozoic Zoophycos occurs in both deep and shallow marine deposits, whereas Mesozoic and Cenozoic Zoophycos is only common in shelfal and deeper-marine deposits. The new finding from the shallow-marine Middle Triassic represents the first reliable occurrence of Zoophycos after the end-Permian mass extinction and shows close similarities to its Palaeozoic precursors. It demonstrates that the producer survived the end-Permian mass extinction, became re-established in the nearshore realm and progressively colonized deeper-marine environments during the Mesozoic and Cenozoic.     

Draft genome sequences of bacteria isolated from the Deschampsia antarctica phyllosphere

Extremophiles - Genome analyses are being used to characterize plant growth-promoting (PGP) bacteria living in different plant compartiments. In this context, we have recently isolated bacteria...     

Floral organ growth and carbohydrate content during pollen development in Lilium

In order to understand floral sugar physiology, we correlated the growth of the organs with carbohydrate content in the flower of Lilium cv. “enchantment” during pollen development. In a previous work, we distinguished two phases in pollen ontogenesis: the anther growth phase, from the microspore mother cell until the vacuolated microspore, and the anther maturation phase, from the vacuolated microspore until anthesis. In the present work, we showed that during the growth phase, the anther underwent most of its size and dry weight growth, whereas the growth rate of nonanther organs was reduced. Anther and filament possessed the highest amounts of carbohydrates, which decreased progressively until the vacuolated microspore stage. During the maturation phase, sucrose and starch increased in all floral organs. Anther growth was completed at the Mi stage, whereas the nonanther organs began exponential growth. From these observations, we concluded that hierarchic nutritional correlations exist between the flower organs, in which the anther is the main actor: during the anther growth phase, the anther represents the highest sink strength floral organ, and mainly attracts assimilates through the filament. During the anther maturation phase, anther growth is achieved, its needs decrease, and assimilates are thus available for neighboring organs, which undergo intense growth until anthesis.     

Diverse bryophyte mesofossils from the Triassic of Antarctica

Compared with the fossil record of vascular plants, bryophyte fossils are rare; this circumstance is probably related to a lower preservation potential compared with that of vascular plants. We searched for bryophyte remains in extensive collections of plant‐fossil assemblages from the Triassic of Antarctica and identified three assemblages with surprisingly well‐preserved bryophyte fossils. Although most bryophyte remains are too fragmented to conclusively place them in a detailed systematic context, they exhibit features sufficient to suggest the presence of at least four types of leafy bryophytes and two orders of thallose liverworts (Pallaviciniales and Metzgeriales) in the high‐latitude Triassic ecosystems of Antarctica. The leafy bryophytes exhibit combinations of morphological features (e.g. keeled and entire‐margined, ecostate leaves with elongated cells) that today occur in only a few small, systematically isolated groups, but were common among Palaeozoic and especially Mesozoic bryophytes. The diverse morphologies of the bryophyte fossils add further support to previous hypotheses that during warmer periods in the Earth's history, bryophyte vegetation may have been particularly rich and diverse in high‐latitude regions. Through analysis of the sedimentology and taphonomy of these assemblages, we identify a combination of key factors that may explain the preservation of bryophyte fossils in these deposits: (1) punctuated, high‐energetic sedimentary events causing traumatic removal and incorporation of bryophytes into sediment‐laden flood waters; (2) limited transport distance, and short period of suspension, followed by rapid settling and burial as a result of a rapidly decelerating flow discharging into a floodplain environment; and (3) early‐diagenetic cementation with iron hydroxides in locally anoxic zones of the organic‐rich, muddy substrate.     

A crocodile from the Upper Triassic of Lesotho

In 1963, a specimen of a small, armoured reptile was discovered in the Red Beds formation in the Qacha's Nek Province of Lesotho, southern Africa. Unfortunately, the matrix in which the specimen is embedded is particularly hard and resistant to chemical action. Preparation must therefore be by mechanical means and is not yet complete. However, certain features of the osteology of the skull and postcranial skeleton of the specimen are clear and are described below.
In both skull and postcranial material, features indicating that this is a relatively advanced crocodilian form are present. It will be shown that on the basis of these characters, this form must be included within the order Crocodilia. It is proposed to name this specimen Ortho-suchus stormbergi.
The discovery of a specimen possessing many diagnostic crocodilian characteristics in Upper Triassic beds is remarkable since hitherto it has been considered that these forms did not appear before the Jurassic. Indeed, our knowledge of Jurassic crocodiles is mainly limited to the more aquatic members owing to the dearth of continental deposits.