Evolution and relationships of the conifer seed cone telemachus: Evidence from the triassic of antarctica

The seed cone Telemachus is known from several Triassic localities in Gondwana. New specimens from two localities in Antarctica provide additional information about the type species, Telemachus elongatus, based on details of morphology and anatomy revealed by using a modified transfer technique on the compressed plants. Seed cones of T. elongatus are up to 6.0 cm long and characterized by conspicuous, elongate bracts. A second Antarctic species, described here as Telemachus antarcticus, is segregated, based on a shorter bract and differences in cone size. Newly recognized features of the genus include the shape, size, and disposition of the ovules; vascularization of the ovuliferous complex; and scale and bract histology. As a result of this new information, it is now possible to compare Telemachus with the permineralized Middle Triassic conifer seed cone Parasciadopitys from the Central Transantarctic Mountains. The similarities between the two genera make it possible to relate organs in different preservational modes and to develop a more complete concept for this widely distributed Gondwana conifer. Placing the Telemachus plant within a phylogenetic context makes it possible to evaluate the relationship with other so-called transitional conifers, an informal group that has been interpreted as intermediate between Paleozoic and modern conifers.Fil: Escapa, Ignacio Hernán. University of Kansas; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Decombeix, Anne-Laure. University of Kansas; Estados UnidosFil: Taylor, Edith L.. University of Kansas; Estados UnidosFil: Taylor, Thomas N.. University of Kansas; Estados Unido

Epicormic Schoots in a Permian Gymnosperm from Antarctica

This is the publisher's version. Shared with permission, it is also available electronically from: http://dx.doi.org/10.1086/654849Two anatomically preserved gymnosperm trunks with clusters of epicormic shoots are described from the Late Permian of Antarctica. The best-preserved trunk is 14 cm long. It has a small circular parenchymatous pith and 9 cm of secondary xylem that contains at least 50 growth rings. The second specimen is slightly smaller (11 3 8 cm) and has 20 growth rings. Both specimens have pycnoxylic wood and produced more than 50 small shoots in a delimited zone on the surface of the trunk. Shoots have a wide parenchymatous pith that may be solid to septate with endarch primary xylem forming 8–10 sympodia and a small amount of secondary xylem similar to that of the parent trunk. The shoots branch and increase in number toward the outside of the trunk. Evidence based on anatomical comparisons and association at the site indicates that the specimens probably represent trunks of some glossopterid, the dominant group of seed ferns during the Permian in Gondwana. This is the first report of clusters of epicormic shoots in a Paleozoic gymnosperm. The ability to produce a large number of young shoots that were capable of developing into new branches indicates that these high-latitude trees possessed an architectural plasticity that allowed them to respond quickly to short- or longterm environmental stress

Secondary Growth in Vertebraria Roots from the Late Permian of Antarctica: A Change in Developmental Timing

This is the publisher's version, also available electronically from http://www.jstor.org/stable/10.1086/597784.Permineralized Vertebraria roots from the late Permian of the Central Transantarctic Mountains, Antarctica, are investigated to understand the unusual vascular anatomy of the genus. The specimens range from ∼1 mm to several centimeters in diameter and illustrate all the stages of secondary growth. Our observations confirm previous hypotheses on the development of these roots and suggest that their unique anatomy is the result of a change in developmental timing. Vertebraria is characterized by a vascular cambium that remains discontinuous through several growth seasons, leading to the formation of lacunae alternating in cross section with wedges of secondary vascular tissues. The bifacial nature of the cambium is confirmed by the presence of well‐developed secondary phloem composed of longitudinally elongated cells and uniseriate parenchymatous rays. In some of the largest specimens, a continuous vascular cylinder is formed by the differentiation of cambium from parenchymatous cells bordering the lacunae. The new specimens provide additional information on the secondary xylem anatomy and vascular connection to lateral roots

Diversity of large woody lignophytes preceding the extinction of Archaeopteris: new data from the middle Tournaisian of Thuringia (Germany)

International audienceAnatomically preserved axes representing three lignophyte species occur in the middle Tournaisian deposit of Kahlleite in Thuringia. One is characterized by a small oval eustele, short uniseriate rays, and alternate distichous phyllotaxy. It is assigned to the progymnosperm genus Protopitys. The two others share a eustelic primary vascular system comprising a parenchymatous pith and numerous xylem strands in a peripheral position. The secondary xylem comprises rays that are mostly uniseriate and rarely exceed 20 cells in height. One is referred to as Eristophyton sp.; the second, characterized by ray cells showing a wide range of sizes and shapes is assigned to Aporoxylon primigenium. These records extend the stratigraphical range of Protopitys and Eristophyton down to the middle Tournaisian and confirm their great longevity through most of the Mississippian. They suggest that the diversity of putative arborescent lignophytes co-occurring with Archaeopteris around the D/C boundary but surviving successfully above this limit has been underestimated

Evolution and Relationships of the Conifer Seed Cone Telemachus: Evidence from the Triassic of Antarctica

This is the publisher's version, also available electronically from http://www.jstor.org/stable/10.1086/651948The seed cone Telemachus is known from several Triassic localities in Gondwana. New specimens from two localities in Antarctica provide additional information about the type species, Telemachus elongatus, based on details of morphology and anatomy revealed by using a modified transfer technique on the compressed plants. Seed cones of T. elongatus are up to 6.0 cm long and characterized by conspicuous, elongate bracts. A second Antarctic species, described here as Telemachus antarcticus, is segregated, based on a shorter bract and differences in cone size. Newly recognized features of the genus include the shape, size, and disposition of the ovules; vascularization of the ovuliferous complex; and scale and bract histology. As a result of this new information, it is now possible to compare Telemachus with the permineralized Middle Triassic conifer seed cone Parasciadopitys from the Central Transantarctic Mountains. The similarities between the two genera make it possible to relate organs in different preservational modes and to develop a more complete concept for this widely distributed Gondwana conifer. Placing the Telemachus plant within a phylogenetic context makes it possible to evaluate the relationship with other so‐called transitional conifers, an informal group that has been interpreted as intermediate between Paleozoic and modern conifers

Early Jurassic silicified woods from Carapace Nunatak, South Victoria Land, Antarctica

The Jurassic vegetation of Antarctica remains poorly known and, while there have been several reports of large fossil trees from that time period across the continent, detailed anatomical studies of their wood are extremely scarce. Here we describe new silicified woods of Early Jurassic (probably Toarcian) age from Carapace Nunatak, South Victoria Land. The genera Agathoxylon and Brachyoxylon are formally recognized for the first time in the Jurassic of Antarctica. The preservation of the woods is imperfect, which is likely explained by the presence in some of the specimens of fungi, whose anatomical structures are described in detail. Combined with previous reports of pollen, leaves, and cones from South and North Victoria Land, these new specimens support the presence of several conifer families in the Early Jurassic floras of the region

A tree without leaves

The puzzle presented by the famous stumps of Gilboa, New York, finds a solution in the discovery of two fossil specimens that allow the entire structure of these early trees to be reconstructed

Origine et diversification des arbres chez les lignophytes du Paléozoïque.

The lignophyte clade includes the free-sporing progymnosperms (Devonian-Carboniferous) and the seed plants, or spermatophytes, that dominate most of present ecosystems. In the context of our studies on the evolution of the arborescent habit in the Palaeozoic, we focussed on the first lignophytes trees. The oldest arborescent lignophytes are the archaeopteridalean progymnosperms that evolved at the end of the Middle Devonian (385 Ma) and became extinct around the Devonian-Carboniferous boundary. Following their extinction, about twenty new taxa interpreted as arborescent members of the protopitylean progymnosperms and of the spermatophytes are recorded in Europe and North America during the Early Carboniferous (Mississippian). Due to incomplete data, particularly concerning their reproduction, the taxonomic relationships of these plants remain doubtful and their importance has often been underestimated. This thesis first documents anatomically preserved specimens of Mississippian age from Montagne Noire (France), Central Sahara (Algeria) and from four basins of Queensland (Australia). These specimens, some of which represent new taxa, illustrate the anatomical diversity of the arborescent lignophytes succeeding to the archaeopteridalean progymnosperms. They document for the first time with confidence, the occurrence of these trees in Gondwana, since the basalmost Mississippian. More generally, these results support a progressive transition between the Devonian Archaeopteridales and the new arborescent lignophytes of the Mississippian. In the second part of the study, we compare the morpho- natomical disparity of the arborescent and non-arborescent lignophytes of the Devonian and Mississippian. An important diversification of the vegetative system is demonstrated among the Mississippian arborescent taxa; this concerns particularly the anatomy of the primary and secondary vascular system and the pattern of lateral organs emission. Finally, a phylogenetic analysis based on a set of mostly vegetative characters is used to test the relationships of some Mississippian taxa whose mode of reproduction is unknown. Arborescent taxa a priori assigned to spermatophytes are effectively included in this clade. They constitute one para- or polyphyletic group and show affinities with some non-arborescent spermatophytes and with the Cordaitales.Le clade des lignophytes comprend d'une part les progymnospermes (Dévonien-Carbonifère) à reproduction par spores, et d'autre part les plantes à graines ou spermatophytes (Dévonien-actuel) qui dominent la majorité des écosystèmes actuels. Dans le cadre de recherches sur l'évolution du port arborescent au Paléozoïque, nous nous sommes intéressés aux premiers arbres apparus dans ce clade. Les plus anciennes lignophytes arborescentes sont les progymnospermes Archaeopteridales qui apparaissent à la fin du Dévonien moyen (385 Ma) et s'éteignent autour de la limite Dévonien-Carbonifère. Après leur disparition, on connait au Carbonifère inférieur (Mississippien) une vingtaine de nouveaux taxons d'Europe et d'Amérique du nord considérés comme arborescents et attribuées aux progymnospermes Protopityales et aux spermatophytes. En raison de l'insuffisance de données, particulièrement sur leur mode de reproduction, les affinités de ces taxons sont incertaines et leur importance a souvent été sous-estimée. Ce travail de thèse documente dans un premier temps des spécimens anatomiquement conservés d'âge Mississippien provenant de la Montagne Noire (France), du Sahara central (Algérie) et de quatre bassins de l'état du Queensland (Australie). Ces spécimens, dont certains représentent de nouveaux taxons, illustrent la diversité taxonomique des lignophytes arborescentes qui succèdent aux Archaeopteridales. Ils documentent pour la première fois avec certitude leur présence en Gondwana, et ce dès le Mississippien inférieur. Plus généralement, ces résultats plaident en faveur d'une transition progressive entre les Archaeopteridales du Dévonien et les nouvelles formes arborescentes du Mississippien. Dans un second temps nous comparons la disparité morpho-anatomique des lignophytes arborescentes et non-arborescentes du Dévonien et du Mississippien. Les résultats mettent notamment en évidence une diversification importante de l'appareil végétatif chez les formes arborescentes du Mississippien ; ceci concerne en particulier l'anatomie du système vasculaire primaire et secondaire et le mode d'émission des organes latéraux. Enfin, une analyse phylogénétique basée sur un jeu de caractères essentiellement végétatifs a permis de tester les affinités de taxons mississippiens dont le mode de reproduction est inconnu. Les formes arborescentes attribuées a priori aux spermatophytes, se placent effectivement dans ce clade. Elles forment un groupe para- ou polyphylétique et présentent des affinités avec des spermatophytes non-arborescentes et avec les Cordaitales

Diversité et biologie des plantes au Paléozoïque et début du Mésozoïque : des premiers arbres aux forêts polaires.

Je présente ici une synthèse des travaux que j’ai mené ces 11 dernières années sur des plantes du Paléozoique et début du Mésozoique (environ -400 à -200 Ma) avec pour objectifs d’identifier la diversité végétale dans le registre fossile et de comprendre comment se structure cette diversité. Ce travail se base sur l’étude de spécimens de collections ainsi que sur du matériel inédit collecté lors de plusieurs missions en particulier en Australie et en Antarctique.Une partie de ce travail se fait à travers des approches classiques en paléontologie qui visent à documenter la diversité taxonomique et la distribution paléogéographique et stratigraphique des plantes fossiles. La 1ère grande thématique qui m’intéresse depuis ma thèse est celle de la diversité et la distribution des flores du Dévonien et du Carbonifère. Mes travaux ont permis de mieux comprendre les flores de ces deux périodes à travers la description de fossiles inédits, en particulier de régions peu étudiées du Gondwana comme l’Australie. Ces nouvelles données sont aussi utilisées pour évaluer l’existence possible d’une crise en milieu terrestre à la limite Dévonien-Carbonifère. Nous avons ainsi pu proposer un nouveau scénario de transition entre lignophytes arborescentes du Dévonien et du Carbonifère. Depuis 2008 je travaille aussi sur la composition des flores d’Antarctique au Permien, Trias et Jurassique, quand le climat global chaud permettait la présence de forêts dans les zones de très haute latitude (>70°S). Ces travaux ont notamment permis de documenter la présence en Antarctique de plusieurs nouveaux taxons et de reconstruire deux plantes entières.Parallèlement à cette documentation de la diversité systématique, j’utilise les informations morpho-anatomiques présentes dans les plantes fossiles pour étudier leur biologie. Ce travail se fait par inférence à partir de nos connaissances des plantes actuelles, soit directement par l’observation des structures, soit dans certains cas en passant par des méthodes de modélisation. J’ai ainsi travaillé sur l’évolution du port arborescent et des tissus vasculaires secondaires, l’anatomie des racines, le potentiel de régénération de l’appareil végétatif, ou encore les interactions plantes-champignon

Trees at the pole: the Permian forests of Antarctica

International audienceDuring the Permian, the warming of the global climate from icehouse to hothouse conditions allowed forests to gradually colonize higher latitudes and to extend well beyond the polar circle. Antarctica (then part of the supercontinent Gondwana) was located at approximately the same latitudes than today and sediments document a rapid arrival of plants as the climate warmed. I will present ongoing work on polar forests from the Transantarctic Mountains that were growing at 75°–85°S during the Late Permian. These forests were largely dominated by one extinct group of trees, the Glossopteridales, with an understory of mosses, ferns, lycophytes and sphenophytes (horsetails). Growth ring analysis indicate that the trees were growing much faster than those of boreal forests today, with a productivity more comparable to that found in extant temperate forests. They also had the ability to regenerate their crown by producing adventitious branches, and had a very unique root system. Antarctic fossils also provide information on various types of interactions in these polar ecosystems, with evidence of fungal wood decay, mycorrhizal associations, arthropod activity, and plant-plant facilitation. Together, all this information provides a better of understanding of Late Permian forests in general and raises questions about plant adaptation to high latitude environments on a warmer planet