A major climatic shift, from a glasshouse world to a colder climate with well-developed ice sheets, occurred during the Cenozoic. Such a transition is recorded in both marine and terrestrial records. The latter is more fragmentary and thus comparatively less well known from a climatic point of view. Leaves are abundant fossil remains, which can be used as terrestrial climatic proxies. In this study, several historical collections from France and Belgium were re-investigated. We applied the Climate Leaf Analysis Multivariate Program in order to document the regional past climate from middle Paleocene to middle Miocene in Western Europe. Our analysis suggest relatively cooler conditions during middle Paleocene, followed by a gradual increase of mean annual temperature and precipitation seasonality during late Paleocene; increased temperature seasonality rather than a global cooling at the Eocene-Oligocene transition; an increase of temperature between early and late Oligocene and warm temperate climate in Western Europe similar to other parts of Europe during middle Miocene. These results are broadly consistent with the global trends observed through the Cenozoic era in the marine record. This study provides new quantitative paleoclimatic estimates for various key periods of the Cenozoic era in Western Europe. The consistency of our results with previous studies based on multiples proxies is in favor of the use of historical collections to reconstruct past climates, as long as sufficient sampling is provided. RÉSUMÉ Évolution du climat en Europe occidentale durant le Cénozoïque : apports des collections historiques à travers l'utilisation de la morphologie foliaire. Durant le Cénozoïque, une transition majeure d'un climat chaud et humide vers un climat plus froid avec des calottes glaciaires bien développées, est observée. Cette transition est documentée dans les registres fossiles marin et continental. En raison de la nature plus fragmentaire de ce dernier, les conditions climatiques continentales sont comparativement moins bien connues. Parmi les restes de plantes conservées dans les sédiments, les feuilles sont particulièrement abondantes et peuvent être utilisées comme proxy climatique terrestre. Dans cette étude, plusieurs collections historiques de France et de Belgique ont été réétudiées. La méthode Climate Leaf Analysis Multivariate Program a été appliquée, afin de documenter le climat régional du Paléocène moyen au Miocène moyen en Europe occidentale. Notre analyse suggère des conditions climatiques relativement fraîches pendant le Paléocène moyen, suivies d'une augmentation graduelle de la MAT et de la saisonnalité des précipitations au cours du Paléocène supérieur, une saisonnalité accrue plutôt qu'une baisse de la MAT à la transition Eocène-Oligocène, une augmentation des températures au cours de l'Oligocène et un climat tempéré chaud semblable au reste de l'Europe durant le Miocène moyen. Dans l'ensemble, ces résultats sont cohérents avec les tendances globales observées au cours du Cénozoïque dans le ...

Archaeopterid trees were the main components of most Late Devonian forests. Their aerial axes characterised by a eustele with mesarch primary xylem strands, leaf traces departing radially from cauline bundles and secondary xylem tracheids with radial pits arranged in groups, are referred to the genus Callixylon Zalessky. The nineteen species of Callixylon described to date from North America, North Africa, Europe, Xinjiang and several parts of Russia range from the late Givetian to the Mississippian. In this paper, we describe a new species of Callixylon from two specimens collected in the Famennian locality of Mader el Mrakib in eastern Anti-Atlas. Callixylon wendtii sp. nov. is characterised by the presence of sclerotic nests in the pith, a new character for the genus. Its wood shows narrow rays of variable height, with unevenly distributed ray tracheids. Small vascular traces crossing the wood within the two innermost growth rings are interpreted as evidence for short-lived leaves. This discovery adds to the diversity of the genus Callixylon in an area of northern Gondwana that may have been favourable to the establishment of a diverse community of archaeopterid trees.

The origin of xylem in the Silurian was a major step in plant evolution, leading to diverse growth forms with various mechanical and hydraulic properties. In the fossil record, these properties can only be investigated using models based on extant plant physiology. Regarding hydraulics, previous studies have considered either the properties of a single tracheid or of a set of independent tubes. Here, we use the analogy between the flow of water under tension in a plant and an electrical circuit to develop an extension of Wilson’s single tracheid model to the tissue scale. Upscaling to the tissue-level allows considering wood as a heterogeneous tissue by taking into account differences in tracheid density and the presence of rays. The new model provides a more biologically accurate representation of fossil wood hydraulic properties. The single tracheid and new tissue models are applied to two conspecific specimens of Callixylon (Progymnospermopsida, Archeopteridales) from the Late Devonian of Morocco. Differences are shown at the tissue level that cannot be suspected at the single tracheid level. Callixylon represents the first trees with a conifer-like wood and is a major component of Late Devonian floras world-wide. Our results show that the anatomical disparity of its wood might have led to hydraulic plasticity, allowing growth in various environmental conditions. More generally, the new tissue-model suggests that the various combinations of tracheid and ray sizes present in Palaeozoic plants might have led to a higher variety of ecophysiologies than suspected based solely on the properties of individual tracheids.

Premise of research. Fossil leaves are commonly used as proxies for continental paleoclimate reconstruction. In particular, temperature and precipitation variables are derived from taxon-free methods using only fossil leaf morphology. Although there is a general relationship between leaf form and climate at a global scale, possible differences between and within angiosperm families remain little explored.Methodology. In this article, we analyzed the influence of phylogenetic relatedness and climate on leaf architecture in 30 species of Cinnamomum (Lauraceae). Nineteen morphological features were selected and documented on the basis of digitized herbarium specimens. Repeatability was measured for all traits. Phylogenetic signal was measured using Blomberg's K. The relationship between morphological variables and climatic variables was investigated using univariate and multivariate statistical approaches.Pivotal results. Our analysis revealed that phylogenetic signal was mainly observed in traits linked to the venation pattern. Size-and shape-related variables are more influenced by climatic parameters than by historical constraints. Cinnamomum leaf morphology is significantly correlated with mean annual temperature and temperature seasonality.Conclusions. Shape and size are representative of convergent temperature-related characters in this genus. Our analysis validates the use of this genus for taxon-free paleoclimatic reconstruction methods relying on such data. The absence of phylogenetic signal in size-and shape-related traits contrasts with earlier studies on distantly related taxa and confirms that historical constraint on leaf morphology is variable among families.

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