Diversity patterns of the vascular plant group Zosterophyllopsida

International audienceZosterophylls were prominent components of the Early Devonian Eophytic flora. However, the diversity studies of early vascular plants have paid little attention to the particular dynamics of this group. To address this concern, we prepared a relational database management system at the species-level to explore the fossil record of the Zosterophyllopsida. From this, a set of diversity metrics and sampling-corrected (so-called residual diversity) curves were used to analyze the temporal and spatial dimensions of palaeodiversity. Results highlight that the diversity dynamics of the Zosterophyllopsida is characterized by a sustained increase of species diversity from the Silurian-Devonian boundary to the end-Pragian followed by a large depletion during the Emsian and a small recovery phase in the Eifelian, after which only minor fluctuations are observed until the end-Devonian. Residual diversity reveals that both the heyday and the main fall of diversity are not driven by sampling. In addition, the taxic composition of five putative palaeophytogeographic units, Laurussia, Siberia, northwestern Gondwana, Kazakhstan and northeastern Gondwana (i.e. Australia, China and the Shan-Thai block) was compared. The high level of endemicity shown by each unit confirms the phytogeographic differentiation and the occurrence of geographical barriers preventing massive floral exchanges between the corresponding regions for the Late Silurian-Early Devonian time interval. Statistical analyses were conducted on the three largest datasets, those corresponding to Laurussia, Siberia and northeastern Gondwana. New evidence indicates that the diversity dynamics of the group followed the same pattern in these regions, showing greatest diversity during the Pragian and sustained levels of extinction thereafter. By contrast, residual diversity reveals regional patterns. The radiation of the Zosterophyllopsida may have stopped earlier in northeastern Gondwana and Siberia than Laurussia. We propose that the onset of the extinctions resulted from the competitive replacement of the zosterophyllopsids by increasingly diversified lycopsids and basal euphyllophytes whose evolution would have been favoured by external factors, possibly the sea-level changes observed in the Pragian. This research was funded by Project ANR-2010-BLAN-607-02 "TERRES"

Estudio paleobotánico e implicaciones paleocimáticas de los restos fósiles vegetales hallados en el cenozoico de la zona surpirenaica central o occidental de la provincia de Huesca

Actualmente, los afloramientos documentados de macroflora cenozoica de Aragón se limitan a los yacimientos de Rubielos de Mora (Teruel), Libros (Teruel) y Épila (Zaragoza), junto a los yacimientos descritos en esta tesis. No obstante, es importante mencionar los numerosos fósiles de plantas citados en los informes de prospección de lignitos terciarios llevados a cabo en la cuenca del Ebro, Pirineo aragonés y en la provincia de Teruel realizados por el Instituto Geológico y Minero de España. Estos restos no están estudiados ni publicados, pero muestran la existencia de otras áreas potenciales para el descubrimiento de nuevosyacimientos paleobotánicos en el Cenozoico.En la paleobotánica española, el estudio de la vegetación del Cenozoico ha estado casi siempre centrado en el Neógeno (Mioceno–Plioceno) y el Cuaternario, estando el Paleógeno (Paleoceno–Eoceno–Oligoceno) poco estudiado, en comparación con las otras Épocas, y focalizado principalmente en el Oligoceno Inferior. El descubrimiento de dos nuevos yacimientos paleobotánicos (Estadilla/La Val, Arguis/Casa Migalón) con suficiente material para estudio en la zona limítrofe entre el Prepirineo y la cuenca del Ebro (provincia deHuesca), así como el interés de su edad (Eoceno Medio y Oligoceno Superior), ha llevado a larealización de esta tesis doctoral. En esta tesis se describen diversos restos de fósiles vegetales (hojas, frutos y endocarpos), incluyendo el primer estudio de las interacciones planta–insecto del OligocenoSuperior de la Península Ibérica en el yacimiento de La Val, Estadilla (Huesca). A su vez, tras la determinación taxonómica y estudio tafonómico, se han obtenido diversas deducciones paleoambientales: paleoclimáticas y paleoecológicas. Este estudio está formado de cuatro publicaciones independientes con una misma unidad temática: tres para el yacimiento de La Val (Estadilla, Huesca, España) y una para el yacimiento de Casa Migalón (Arguis, Huesca, España). La edad del yacimiento de La Val, tanto de su macroflora como de sus interacciones planta–insecto, es Chatiense (Oligoceno Superior), mientras que los endocarpos y frutos de Nypa del yacimiento de Casa Migalón es Bartoniense (Eoceno Medio). Los primeros resultados del estudio del yacimiento de La Val se han plasmado en una primera publicación sobre la macroflora. Estos resultados han incluído aspectos taxonómicos y tafonómicos, así como una primera aproximación paleoecológica y paleoclimática donde se compara la composición de dicha flora con otras floras similares a las del resto de Europa. En el segundo trabajo se completan los datos mostrados en el artículo precedente y se redefine la edad del yacimiento. La segunda publicación recoge además el estudio del medio sedimentario del yacimiento, así como las implicaciones paleoecológicas derivadas de la presencia del helecho Acrostichum lanzaeanum. En el tercer artículo y último relativo al yacimiento de La Val, se describen las primerasinteracciones planta–insecto encontradas sobre las hojas de uno de los niveles fosilíferos, realizando una discusión para determinar sus implicaciones paleoclimáticas, cuyas conclusiones han matizado y completado la paleoclimatología inferida en el primer trabajo. La cuarta y última publicación que conforma esta tesis ha versado sobre los frutos y endocarpos fósiles de Nypa encontrados en el yacimiento de Casa Migalón (Arguis, Huesca). En este trabajo se llevó a cabo un estudio taxonómico, tafonómico y paleoambiental. Es importante destacar que este artículo se centra especialmente en un aspecto tafonómico muy poco conocido como es la duración del tiempo de flotación en el mar de este tipo de restos hasta su depósito definitivo.<br /

Stepwise evolution of Paleozoic tracheophytes from South China: contrasting leaf disparity and taxic diversity

During the late Paleozoic, vascular land plants (tracheophytes) diversified into a remarkable variety of morpho- logical types, ranging from tiny, aphyllous, herbaceous forms to giant leafy trees. Leaf shape is a key determinant of both function and structural diversity of plants, but relatively little is known about the tempo and mode of leaf morphological diversification and its correlation with tracheophyte diversity and abiotic changes during this re- markable macroevolutionary event, the greening of the continents. We use the extensive record of Paleozoic tra- cheophytes from South China to explore models of morphological evolution in early land plants. Our findings suggest that tracheophyte leaf disparity and diversity were decoupled, and that they were under different selec- tive regimes. Two key phases in the evolution of South Chinese tracheophyte leaves can be recognized. In the first phase, from Devonian to Mississippian, taxic diversity increased substantially, as did leaf disparity, at the same time as they acquired novel features in their vascular systems, reproductive organs, and overall architecture. The second phase, through the Carboniferous–Permian transition, saw recovery of wetland communities in South China, associated with a further expansion of morphologies of simple leaves and an offset shift in morphospace occupation by compound leaves. Comparison with Euramerica suggests that the floras from South China were unique in several ways. The Late Devonian radiation of sphenophyllaleans contributed signif- icantly to the expansion of leaf morphospace, such that the evolution of large laminate leaves in this group oc- curred much earlier than those in Euramerica. The Pennsylvanian decrease in taxic richness had little effect on the disparity of compound leaves. Finally, the distribution in morphospace of the Permian pecopterids, gigantopterids, and equisetaleans occurred at the periphery of Carboniferous leaf morphospace

Disentangling temporal patterns in our perception of the fossil history of gymnosperms

By taking gymnosperms as a case study, this article evaluates the perception of plant life history from the fossil record to test the biases associated with the time-dependent aspects of the taxonomy, following a stepwise modelling procedure based on two divergent sets of time units. The idea that the effects of the temporal component of paleobiological inference need to be evaluated to remove any possible bias in our interpretation and perception of plant evolution based on analyses of large-scale data sets is investigated. The results reveal important differences in our perception of the tempo of gymnosperm evolution and how it is biased in terms of time unit length due to the loss of information as a consequence of the timescale resolution. Despite singletons representing real morphological diversity translated into independent taxonomic categories, these taxa can distort perceptions of the intensity of the long paleofloristic diversification moments of gymnosperms if their effect is not considered. This study shows a complete overview of the evolutionary profiles of gymnosperms with significant discrepancies in the function of how singletons are quantitatively processed in paleobotanical data analyses, and it provides new evidence about how the 'zoom effect' can magnify our perception of extinction events. © 2012 Copyright Taylor and Francis Group, LLC

On the plant diversity changes during the Ordovician-Mississippian time interval

peer reviewe

New insights into the reading of Paleozoic plant fossil record discontinuities

Studying the discontinuity patterns of Paleozoic vascular plants provides a global vision of these key events from the multivariate methods viewpoint. Non-metric multidimensional scaling, detrended correspondence analysis and cluster analysis have been employed together with a set of diversity and abundance measures and an evaluation of the geologic constraints from the plant fossil record data. The results reveal four clear significant discontinuities in terms of taxonomic composition and record representativeness during the early-middle Devonian, Devonian-Carboniferous, Mississippian-Pennsylvanian and early-late Permian. Due to the controversial character of the plant fossil record data and the effect of mass extinction events, the results can be explained in taxonomic turnover and ecological reorganisation terms which emphasise the crucial role of the geologic constrains in paleobiological inference. © 2011 Taylor & Francis

Testing similarity coefficients for analysis of the fossil record using clustering methods: The Palaeozoic flora as a study case

peer reviewedThis paper reports a global methodological approach based on the similarity and clustering methods of the Palaeozoic plant fossil record using a comparative approach between two similarity measures: the Jaccard and Raup-Crick Coeffcients. The results show that although the Raup-Crick Coeffcients clearly have the potential for providing more robust results, the consequences of the extinction processes are better refected in the similarity analysis based on the Jaccard Coeffcients. On the other hand, the cluster analysis based on UPGMA algorithm shows four robust clusters and reveals new evidence for the singularity of Mississippian fora. Finally, the results obtained reveal that similarity and cluster analysis are powerful tools to interpret the consequence of the processes modifying the taxonomic composition of the several analyzed Palaeozoic time units

Apparent changes of the Ordovician-Mississippian plant diversity

International audienceThis study aims to approximate an illustrative vision of the apparent temporal dynamics of land plant diversity during the terrestrialization process (i.e., the invasion of the land by plants). This problem has often been addressed through studying the Silurian–Devonian megafossil-based diversity patterns of land plants (embryophytes). However, the inclusion of the dispersed spore fossil record is essential for characterizing the first steps of this process (i.e., Eoembryophytic flora). Consequently, this new study includes both spore taxa and plant megafossils in order to discern the diversity trajectories from the first phases of early land plant diversification until the stabilization of early Carboniferous forests (i.e., Palaeophytic flora). The diversity patterns of the primary recognized plant lineages (i.e., Lycophyta and Euphyllophyta) have been also traced in order to discern the origin of the major fluctuations of plant megafossil-based diversity. Results reveal that while the dispersed spore diversity curve shows a sustained increase towards the end of the Devonian Period – with a first maximum towards the late Silurian – the megafossil embryophyte diversity curve is characterized by a set of sequential ascending peaks at the Pragian (Early Devonian), Givetian (Mid-Devonian), and Visean (Mississippian), with a single significant depletion in the Eifelian (Mid-Devonian). The comparative analysis of the lycophyte and euphyllophyte diversity patterns suggests that the substantial embryophytic diversity changes are driven by diversification within lineages rather than by the rhythm of the appearance of key morphological traits. This evidence (1) advocates for an intrinsic ecological control on the apparent changes in taxic richness and (2) implies that the observed plant diversity dynamics respond to the overlapping of the various expansion phases of the plant lineages involved