Paleophysiology of Permian and Triassic Seed Plants

This study utilized both anatomically and morphologically preserved fossil plants to investigate plant paleophysiology using known form/function relationships. The fossils examined in this project come from fossil localities ideal for studying various paleophysiological relationships. At the beginning of the Permian Period (~299 Ma), atmospheric CO2 and O2 concentrations were comparable to current day values. By the end of the Permian (~251 Ma), atmospheric CO2 concentration and temperature had risen sharply as the Earth underwent a time of rapid global warming. The distinctive leaf of Glossopteris plants can be found at southern high paleolatitude localities throughout the Permian, allowing for changes in plant physiology to be tracked through a drastically shifting climate. The environmental conditions at the beginning of the Permian are also the same as those that are thought to have favored the evolution of the C4 photosynthetic pathway in the Oligocene (~25 Ma). Using known relationships between leaf anatomy and the C4 pathway, along with stable carbon isotope analysis, the presence or absence of this pathway was tested. The combination of both approaches demonstrated the C3-C4 intermediate photosynthetic pathway was present in Glossopteris during the Late Permian. In the ancient past, plants existed in warm environments at high paleolatitudes where they were subjected to light regimes not experienced by plants today (4 months of continuous light and 4 months of continuous dark). A study of leaf economics of Permian Glossopteris leaves reveals that the plant possessed deciduous leaves and adaptations to continuous light environments. Analysis of Permian and Triassic leaf hydraulic conductance demonstrates that leaf venation density in Glossopteris decreases in response to increasing CO2 but does not change in response to latitude. Glossopteris leaves, which dominated the Permian landscapes of Antarctica, demonstrated a higher leaf venation density than any co-occurring leaves. Such an advantage would benefit leaf hydraulic conductance. In contrast, the Dicroidium leaf type, which dominated the Triassic, had leaf hydraulic values similar to co-occuring leaf morphotypes

Whole-plant concept and environment reconstruction of a Telemachus Conifer (Voltziales) from the triassic of Antarctica

International audienceWe present a whole-plant concept for a genus of voltzialean conifers on the basis of compression/impression and permineralized material from the Triassic of Antarctica. The reconstruction of the individual organs is based on a combination of organic connections, structural correspondences, similarities in cuticles and epidermal morphologies, co-occurrence data, and ex situ palynology. The affiliated genera of organs include trunks, branches, and roots (Notophytum); strap-shaped leaves with parallel venation (Heidiphyllum compressions and permineralized Notophytum leaves); seed cones (Telemachus and Parasciadopitys); pollen cones (Switzianthus); and bisaccate pollen of Alisporites type. Structural similarities lead us to suggest that Parasciadopitys is the permineralized state of a Telemachus cone and should be treated as a junior synonym. Biotic interactions involving the reconstructed conifer genus include plant-insect interactions (oviposition by Odonata) and not less than five different types of plant-fungal interactions, including two distinct endomycorrhizal associations, two probable seed parasites, and epiphyllous fungi. A representative whole plant is reconstructed as a 10-15-m-tall, seasonally deciduous forest tree with a vertical, narrow-conical crown shape. We interpret these Telemachus trees as the dominant components of peat-forming conifer swamps, forest bogs, and immature bottomland vegetation in the Triassic high-latitude river basins of southern Gondwana. In architecture, growth habit, and many ecological characteristics, the Telemachus conifers appear to be comparable to extant larch (Larix). Owing to the large amount and often exquisite preservation of the material, this conceptual whole-plant genus represents one of the most completely reconstructed ancient conifer taxa to dat

Habit and Ecology of the Petriellales, an Unusual Group of Seed Plants from the Triassic of Gondwana

Premise of research. Well-preserved Triassic plant fossils from Antarctica yield insights into the physiology of plant growth under the seasonal light regimes of warm polar forests, a type of ecosystem without any modern analogue. Among the many well-known Triassic plants from Antarctica is the enigmatic Petriellaea triangulata, a dispersed seedpod structure that is considered a possible homologue of the angiosperm carpel. However, the morphology and physiology of the plants that produced these seedpods have so far remained largely elusive. Methodology. Here, we describe petriellalean stems and leaves in compression and anatomical preservation that enable a detailed interpretation of the physiology and ecology of these plants. Pivotal results. Our results indicate that the Petriellales were diminutive, evergreen, shade-adapted perennial shrubs that colonized the understory of the deciduous forest biome of polar Gondwana. This life form is very unlike that of any other known seed-plant group of that time. By contrast, it fits remarkably well into the “dark and disturbed” niche that some authors considered to have sheltered the rise of the flowering plants some 100 Myr later. Conclusions. The hitherto enigmatic Petriellales are now among the most comprehensively reconstructed groups of extinct seed plants and emerge as promising candidates for elucidating the mysterious origin of the angiosperms