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Sergio N. Santillana – One of the best experts on this subject based on the ideXlab platform.

  • Conifer Fossil Woods from the Sobral Formation (Lower Paleocene, Western Antarctica)
    Ameghiniana, 2018
    Co-Authors: Sebastian Luis Mirabelli, Roberto R. Pujana, Sergio A. Marenssi, Sergio N. Santillana

    Abstract:

    Conifer fossil woods represent 54% of an assemblage of 116 specimens collected from sediments of the Sobral Formation in Seymour (Marambio) Island, Western Antarctica. These woods are anatomically described in detail and assigned to seven fossil-species of the following fossil-genera: Agathoxylon (Araucariaceae), Podocarpoxylon, Phyllocladoxylon, Protophyllocladoxylon (Podocarpaceae), and Cupressinoxylon (Podocarpaceae/Cupressaceae). The conifer wood assemblage reveals that the most common woods are those of Agathoxylon, therefore indicating a relative abundance of the Araucariaceae in the Antarctic Paleocene forests. This abundance of the Araucariaceae woods is locally continued in the overlying Cross Valley Formation (Paleocene). Podocarpaceae woods are found in almost similar proportions to those of the Araucariaceae. Almost the other half of the fossil woods are dicotyledon woods. The proportions of the identified fossil wood taxa are consistent with those of the palynological studies of the same stratigraphic unit.

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  • CONIFER FOSSIL WOODS FROM THE SOBRAL FORMATION (LOWER PALEOCENE, WESTERN ANTARCTICA) — Preprint doi:10.5710/AMGH.27.07.2017.3095
    Ameghiniana, 2015
    Co-Authors: Sebastian Luis Mirabelli, Roberto R. Pujana, Sergio A. Marenssi, Sergio N. Santillana

    Abstract:

    Conifer fossil woods represent the 54% of an assemblage of 116 specimens collected from sediments of the Sobral Formation in the Seymour (Marambio) Island, Western Antarctica. These woods are anatomically described in detail and assigned to seven fossil-species of the following fossil-genera: Agathoxylon (Araucariaceae), Podocarpoxylon, Phyllocladoxylon and Protophyllocladoxylon (Podocarpaceae) and Cupressinoxylon (Podocarpaceae/Cupressaceae). The conifer wood assemblage reveals that the most common woods are those of Agathoxylon indicating a relative abundance of the Araucariaceae in the Antarctic Paleocene forests. This abundance of the Araucariaceae woods is locally continued in the overlying Cross Valley Formation (Paleocene). Podocarpaceae woods are found in almost similar proportions to those of the Araucariaceae. Almost the other half of the fossil woods are dicotyledon woods. Proportions of the identified fossil wood taxa are consistent with those of the palynological studies of the same stratigraphic unit.

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  • Fossil woods from the Cross Valley Formation (Paleocene of Western Antarctica): Araucariaceae-dominated forests
    Review of Palaeobotany and Palynology, 2015
    Co-Authors: Roberto R. Pujana, Sergio A. Marenssi, Sergio N. Santillana

    Abstract:

    Fossil woods from Paleocene sediments of the Cross Valley Formation (Seymour Island, Antarctic Peninsula) are anatomically studied in detail. We collected 64 samples represented almost exclusively by conifers (95%). Only three samples of not determinable angiosperm fossil wood were found. Preservation of the samples is often poor and 52% of the samples were assigned to a fossil-species. The assemblage is dominated by Agathoxylon (Araucariaceae), particularly Agathoxylon antarcticus. Araucariaceae species are joined by Protophyllocladoxylon, Phyllocladoxylon and Cupressinoxylon. Forests dominated by Araucariaceae are unusual during the Cenozoic. The high dominance of Araucariaceae woods may be a reflection of soil conditions, weather and terrain elevation. Our study supports previous hypothesis that identified differences between the paleofloras in each side of the Antarctic Peninsula during the Paleocene.

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Jennifer C. Mcelwain – One of the best experts on this subject based on the ideXlab platform.

  • The stomatal CO_2 proxy does not saturate at high atmospheric CO_2 concentrations: evidence from stomatal index responses of Araucariaceae conifers
    Oecologia, 2011
    Co-Authors: Matthew Haworth, Caroline Elliott-kingston, Jennifer C. Mcelwain

    Abstract:

    The inverse relationship between the number of stomata on a leaf surface and the atmospheric carbon dioxide concentration ([CO_2]) in which the leaf developed allows plants to optimise water-use efficiency (WUE), but it also permits the use of fossil plants as proxies of palaeoatmospheric [CO_2]. The ancient conifer family Araucariaceae is often represented in fossil floras and may act as a suitable proxy of palaeo-[CO_2], yet little is known regarding the stomatal index (SI) responses of extant Araucariaceae to [CO_2]. Four Araucaria species ( Araucaria columnaris , A. heterophylla , A. angustifolia and A. bidwillii ) and Agathis australis displayed no significant relationship in SI to [CO_2] below current ambient levels (~380 ppm). However, representatives of the three extant genera within the Araucariaceae ( A. bidwillii , A. australis and Wollemia nobilis ) all exhibited significant reductions in SI when grown in atmospheres of elevated [CO_2] (1,500 ppm). Stomatal conductance was reduced and WUE increased when grown under elevated [CO_2]. Stomatal pore length did not increase alongside reduced stomatal density (SD) and SI in the three araucariacean conifers when grown at elevated [CO_2]. These pronounced SD and SI reductions occur at higher [CO_2] levels than in other species with more recent evolutionary origins, and may reflect an evolutionary legacy of the Araucariaceae in the high [CO_2] world of the Mesozoic Era. Araucariacean conifers may therefore be suitable stomatal proxies of palaeo-[CO_2] during periods of “greenhouse” climates and high [CO_2] in the Earth’s history.

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  • The stomatal CO2 proxy does not saturate at high atmospheric CO2 concentrations: evidence from stomatal index responses of Araucariaceae conifers.
    Oecologia, 2011
    Co-Authors: Matthew Haworth, Caroline Elliott-kingston, Jennifer C. Mcelwain

    Abstract:

    The inverse relationship between the number of stomata on a leaf surface and the atmospheric carbon dioxide concentration ([CO2]) in which the leaf developed allows plants to optimise water-use efficiency (WUE), but it also permits the use of fossil plants as proxies of palaeoatmospheric [CO2]. The ancient conifer family Araucariaceae is often represented in fossil floras and may act as a suitable proxy of palaeo-[CO2], yet little is known regarding the stomatal index (SI) responses of extant Araucariaceae to [CO2]. Four Araucaria species (Araucaria columnaris, A. heterophylla, A. angustifolia and A. bidwillii) and Agathis australis displayed no significant relationship in SI to [CO2] below current ambient levels (~380 ppm). However, representatives of the three extant genera within the Araucariaceae (A. bidwillii, A. australis and Wollemia nobilis) all exhibited significant reductions in SI when grown in atmospheres of elevated [CO2] (1,500 ppm). Stomatal conductance was reduced and WUE increased when grown under elevated [CO2]. Stomatal pore length did not increase alongside reduced stomatal density (SD) and SI in the three araucariacean conifers when grown at elevated [CO2]. These pronounced SD and SI reductions occur at higher [CO2] levels than in other species with more recent evolutionary origins, and may reflect an evolutionary legacy of the Araucariaceae in the high [CO2] world of the Mesozoic Era. Araucariacean conifers may therefore be suitable stomatal proxies of palaeo-[CO2] during periods of “greenhouse” climates and high [CO2] in the Earth’s history.

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Roberto R. Pujana – One of the best experts on this subject based on the ideXlab platform.

  • Fossil woods from the Lower Cretaceous Tres Lagunas Formation of central Patagonia (Chubut Province, Argentina)
    Cretaceous Research, 2020
    Co-Authors: Carlos Daniel Greppi, Roberto R. Pujana, Roberto A. Scasso

    Abstract:

    Abstract Silicified fossil woods are common in the Tres Lagunas Formation (Lower Cretaceous) of central Patagonia. This region has a poor record of Early Cretaceous fossil woods. A collection of 23 fossil woods is studied. Fossil wood anatomy is described and compared in detail. The wood flora is composed of conifers. Most of the samples have Araucariaceae-like wood anatomy. The samples are placed into seven taxonomic units: three fossil-species of Agathoxylon, two more taxonomic units related to Agathoxylon, one taxonomic unit consistent with Cupressinoxylon? and one fossil-species of Brachyoxylon. This study indicates a dominance of conifers, particularly Araucariaceae, during the Early Cretaceous of this zone of central Patagonia which partially does not coincide with the taxonomic proportions of previous studies of coeval pollen and plant macrofossils.

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  • Conifer Fossil Woods from the Sobral Formation (Lower Paleocene, Western Antarctica)
    Ameghiniana, 2018
    Co-Authors: Sebastian Luis Mirabelli, Roberto R. Pujana, Sergio A. Marenssi, Sergio N. Santillana

    Abstract:

    Conifer fossil woods represent 54% of an assemblage of 116 specimens collected from sediments of the Sobral Formation in Seymour (Marambio) Island, Western Antarctica. These woods are anatomically described in detail and assigned to seven fossil-species of the following fossil-genera: Agathoxylon (Araucariaceae), Podocarpoxylon, Phyllocladoxylon, Protophyllocladoxylon (Podocarpaceae), and Cupressinoxylon (Podocarpaceae/Cupressaceae). The conifer wood assemblage reveals that the most common woods are those of Agathoxylon, therefore indicating a relative abundance of the Araucariaceae in the Antarctic Paleocene forests. This abundance of the Araucariaceae woods is locally continued in the overlying Cross Valley Formation (Paleocene). Podocarpaceae woods are found in almost similar proportions to those of the Araucariaceae. Almost the other half of the fossil woods are dicotyledon woods. The proportions of the identified fossil wood taxa are consistent with those of the palynological studies of the same stratigraphic unit.

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  • CONIFER FOSSIL WOODS FROM THE SOBRAL FORMATION (LOWER PALEOCENE, WESTERN ANTARCTICA) — Preprint doi:10.5710/AMGH.27.07.2017.3095
    Ameghiniana, 2015
    Co-Authors: Sebastian Luis Mirabelli, Roberto R. Pujana, Sergio A. Marenssi, Sergio N. Santillana

    Abstract:

    Conifer fossil woods represent the 54% of an assemblage of 116 specimens collected from sediments of the Sobral Formation in the Seymour (Marambio) Island, Western Antarctica. These woods are anatomically described in detail and assigned to seven fossil-species of the following fossil-genera: Agathoxylon (Araucariaceae), Podocarpoxylon, Phyllocladoxylon and Protophyllocladoxylon (Podocarpaceae) and Cupressinoxylon (Podocarpaceae/Cupressaceae). The conifer wood assemblage reveals that the most common woods are those of Agathoxylon indicating a relative abundance of the Araucariaceae in the Antarctic Paleocene forests. This abundance of the Araucariaceae woods is locally continued in the overlying Cross Valley Formation (Paleocene). Podocarpaceae woods are found in almost similar proportions to those of the Araucariaceae. Almost the other half of the fossil woods are dicotyledon woods. Proportions of the identified fossil wood taxa are consistent with those of the palynological studies of the same stratigraphic unit.

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