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Christian Pott - One of the best experts on this subject based on the ideXlab platform.
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westersheimia pramelreuthensis from the carnian upper triassic of lunz austria more evidence for a unitegmic seed coat in early Bennettitales
International Journal of Plant Sciences, 2016Co-Authors: Christian PottAbstract:Premise of research. Isolated ovules and dispersed seeds have been obtained from bulk macerations of carbonaceous shales bearing fossil plants from the Carnian (Upper Triassic) flora of Lunz am See, Austria. Through cuticle analysis, these well-preserved specimens were identified as ovules, interseminal scales, and seeds of Westersheimia pramelreuthensis, a peculiar bennettitalean ovuliferous organ. The preservation of several cuticular layers enables for interpretation of the architecture of the ovules and seeds.Methodology. The excellently preserved plant fossils were investigated using LM and epifluorescence microscopy of cuticles. For comparison, the architecture of ovules and seeds of bennettitalean reproductive organs from Scania (Sweden), Jameson Land (Greenland), and Yorkshire (United Kingdom) were reevaluated.Pivotal results. The preserved layers indicate that the nucellus is surrounded by an integument, whose apical end constitutes the micropyle. The single integument constitutes the monolayered...
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Bennettitales in the rhaetian flora of wustenwelsberg bavaria germany
Review of Palaeobotany and Palynology, 2016Co-Authors: Christian Pott, Stefan Schmeisner, Gunter Dutsch, Johanna H A Van Konijnenburgvan CittertAbstract:The diverse bennettitalean plant remains from the Rhaetian of Wustenwelsberg, Franconia, southern Germany,are described by means of macromorphological and epidermal anatomy; the study is part of th ...
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williamsonia carolinensis sp nov and associated eoginkgoites foliage from the upper triassic pekin formation north carolina implications for early evolution in the williamsoniaceae Bennettitales
International Journal of Plant Sciences, 2015Co-Authors: Christian Pott, Brian J AxsmithAbstract:Premise of research. Few reproductive organs unequivocally attributable to the important but enigmatic Mesozoic seed plant order Bennettitales have been described from the Triassic of all of North America outside of Greenland. Here, the first ovulate reproductive organs (gynoecia) of the group from the Upper Triassic of eastern North America are described and assigned to a proposed new species, Williamsonia carolinensis, of the family Williamsoniaceae.Methodology. The excellently preserved plant fossils were investigated using cuticular analysis and light, fluorescence, and scanning electron microscopy.Pivotal results. The description is based on 10 specimens from the Late Triassic (Carnian) Pekin Formation of North Carolina. They are interpreted as representing progressive developmental stages. Williamsonia carolinensis lacks a corona (sterile apical projection of the receptacle) and bracts subtending the receptacle. The lack of bracts is particularly unusual and appears to be the original condition and ...
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Divaricate growth habit in Williamsoniaceae (Bennettitales): unravelling the ecology of a key Mesozoic plant group
Palaeobiodiversity and Palaeoenvironments, 2014Co-Authors: Christian Pott, Stephen McloughlinAbstract:Representatives of Williamsoniacae (Bennettitales) are usually restored as small-leafed shrubs or low-growing trees with densely interlaced stems bifurcating or trifurcating at broad angles—a growth form referred to as divaricating. A divaricate plant architecture has evolved independently in at least 18 modern plant families, of which the majority occur in New Zealand, where they constitute more than 10 % of the flora. Botanists favour two or three hypotheses on the benefits of a divaricating habit for modern plants. One hypothesis favours the evolution of this habit to protect the foliage and reproductive structures from browsing by large mammals or large flightless birds, such as the recently extinct moa or other ratites. Another argues that this habit evolved in response to a dry, windy or frosty climate, whereas a third regards divarication as having evolved to optimise foliar light harvesting. Our evaluation of these hypotheses with respect to the ecological pressures known to have been experienced by Williamsoniaceae in the mid-Mesozoic reveals that although defence against browsing tetrapods cannot be excluded as a selective pressure that promoted divarication in Williamsoniaceae, many of the anatomical and morphological features of this family appear to represent responses to local environmental conditions. In this context, representatives of Williamsoniaceae have many characters that are convergent with members of Banksiinae (Proteaceae), suggesting adaptation to open vegetation communities on nutrient-deficient soils.
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trichomes on the leaves of anomozamites villosus sp nov Bennettitales from the daohugou beds middle jurassic inner mongolia china mechanical defence against herbivorous arthropods
Review of Palaeobotany and Palynology, 2012Co-Authors: Christian Pott, Stephen Mcloughlin, Wu Shunqing, Else Marie FriisAbstract:The abaxial leaf surfaces of Anomozamites villosus sp. nov., a new species of bennettitalean foliage from the Middle Jurassic Daohugou beds of Inner Mongolia, China, are covered with soft, shaggy hairs that are loosely, but regularly distributed across the lamina. Selectively arranged, long, stiff or acerate hairs directed or bent towards the leaf apex, project on the abaxial side of the leaf from the rachis margins. Both types of hairs are interpreted predominantly as adaptations for passive defence against damage by arthropods (sap-sucking, leaf-chewing or oviposition) rather than being morphological responses to physical environmental parameters, e.g. xeromorphic features. As several of the leaves show evidence for high levels of leaf-margin feeding by phytophagous arthropods, these mechanisms have not been entirely effective and may have evolved to defend against only selected arthropods or behavioural strategies. These findings contribute to the reconstruction of ecological interactions in the exceptionally preserved Jurassic Daohugou biota of northern China, and provide a rare insight into the plant–arthropod co-evolutionary ‘arms race’.
Stephen Mcloughlin - One of the best experts on this subject based on the ideXlab platform.
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molecular signatures of fossil leaves provide unexpected new evidence for extinct plant relationships
Nature Ecology and Evolution, 2017Co-Authors: Vivi Vajda, Stephen Mcloughlin, Milda Pucetaite, Anders Engdahl, Jimmy Heimdal, Per UvdalAbstract:Gene sequences form the primary basis for understanding the relationships among extant plant groups, but genetic data are unavailable from fossils to evaluate the affinities of extinct taxa. Here we show that geothermally resistant fossil cuticles of seed-bearing plants, analysed with Fourier transform infrared (FTIR) spectroscopy and hierarchical cluster analysis (HCA), retain biomolecular suites that consistently distinguish major taxa even after experiencing different diagenetic histories. Our results reveal that similarities between the cuticular biochemical signatures of major plant groups (extant and fossil) are mostly consistent with recent phylogenetic hypotheses based on molecular and morphological data. Our novel chemotaxonomic data also support the hypothesis that the extinct Nilssoniales and Bennettitales are closely allied, but only distantly related to Cycadales. The chemical signature of the cuticle of Czekanowskia (Leptostrobales) is strongly similar to that of Ginkgo leaves and supports a close evolutionary relationship between these groups. Finally, our results also reveal that the extinct putative araucariacean, Allocladus, when analysed through HCA, is grouped closer to Ginkgoales than to conifers. Thus, in the absence of modern relatives yielding molecular information, FTIR spectroscopy provides valuable proxy biochemical data complementing morphological characters to distinguish fossil taxa and to help elucidate extinct plant relationships.
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Divaricate growth habit in Williamsoniaceae (Bennettitales): unravelling the ecology of a key Mesozoic plant group
Palaeobiodiversity and Palaeoenvironments, 2014Co-Authors: Christian Pott, Stephen McloughlinAbstract:Representatives of Williamsoniacae (Bennettitales) are usually restored as small-leafed shrubs or low-growing trees with densely interlaced stems bifurcating or trifurcating at broad angles—a growth form referred to as divaricating. A divaricate plant architecture has evolved independently in at least 18 modern plant families, of which the majority occur in New Zealand, where they constitute more than 10 % of the flora. Botanists favour two or three hypotheses on the benefits of a divaricating habit for modern plants. One hypothesis favours the evolution of this habit to protect the foliage and reproductive structures from browsing by large mammals or large flightless birds, such as the recently extinct moa or other ratites. Another argues that this habit evolved in response to a dry, windy or frosty climate, whereas a third regards divarication as having evolved to optimise foliar light harvesting. Our evaluation of these hypotheses with respect to the ecological pressures known to have been experienced by Williamsoniaceae in the mid-Mesozoic reveals that although defence against browsing tetrapods cannot be excluded as a selective pressure that promoted divarication in Williamsoniaceae, many of the anatomical and morphological features of this family appear to represent responses to local environmental conditions. In this context, representatives of Williamsoniaceae have many characters that are convergent with members of Banksiinae (Proteaceae), suggesting adaptation to open vegetation communities on nutrient-deficient soils.
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trichomes on the leaves of anomozamites villosus sp nov Bennettitales from the daohugou beds middle jurassic inner mongolia china mechanical defence against herbivorous arthropods
Review of Palaeobotany and Palynology, 2012Co-Authors: Christian Pott, Stephen Mcloughlin, Wu Shunqing, Else Marie FriisAbstract:The abaxial leaf surfaces of Anomozamites villosus sp. nov., a new species of bennettitalean foliage from the Middle Jurassic Daohugou beds of Inner Mongolia, China, are covered with soft, shaggy hairs that are loosely, but regularly distributed across the lamina. Selectively arranged, long, stiff or acerate hairs directed or bent towards the leaf apex, project on the abaxial side of the leaf from the rachis margins. Both types of hairs are interpreted predominantly as adaptations for passive defence against damage by arthropods (sap-sucking, leaf-chewing or oviposition) rather than being morphological responses to physical environmental parameters, e.g. xeromorphic features. As several of the leaves show evidence for high levels of leaf-margin feeding by phytophagous arthropods, these mechanisms have not been entirely effective and may have evolved to defend against only selected arthropods or behavioural strategies. These findings contribute to the reconstruction of ecological interactions in the exceptionally preserved Jurassic Daohugou biota of northern China, and provide a rare insight into the plant–arthropod co-evolutionary ‘arms race’.
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ptilophyllum muelleri ettingsh comb nov from the oligocene of australia last of the Bennettitales
International Journal of Plant Sciences, 2011Co-Authors: Stephen Mcloughlin, Raymond J Carpenter, Christian PottAbstract:Several small pinnate leaves of early Oligocene age from Cethana, Tasmania, are newly described and found to be conspecific with Anomozamites muelleri Ettingsh. recorded from coeval strata at Emmaville, northern New South Wales. These fossils are most probably referable to the Bennettitales on the basis of leaf size, leaflet shape, and venation patterns, in the absence of diagnostic cuticular details. They are transferred to Ptilophyllum on the basis of leaflet morphology and represent the youngest putative bennettitalean remains yet documented. Their occurrence reinforces previous arguments that the highest-paleolatitude fragments of southeastern Gondwana provided moist temperate refugia for the survival of Mesozoic gymnosperm taxa well into the Cenozoic.
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late palaeozoic foliage from china displays affinities to cycadales rather than to Bennettitales necessitating a re evaluation of the palaeozoic pterophyllum species
Acta Palaeontologica Polonica, 2010Co-Authors: Christian Pott, Stephen Mcloughlin, Anna LindstromAbstract:The epidermal anatomy of Pseudoctenis samchokense is described revealing non-bennettitalean characters of these leaves from the Permo-Carboniferous of China (and Korea). The specimens were originally described as Pterophyllum samchokense suggesting a bennettitalean affinity. They can no longer be considered bennettitalean since their cuticles lack the distinctive brachyparacytic stomata of that clade. Pterophyllum was originally erected as a morphogenus for segmented leaves from the Mesozoic and has subsequently been clearly assigned to the Bennettitales. The segmented leaves from the Permo-Carboniferous of Shanxi and Hebei, China described herein require a new ordinal and generic assignment since the non-bennettitalean cuticular characters documented reinforce the uncertainties in attribution of any foliage older than Late Triassic to the Bennettitales. Based on leaf-architecture and epidermal anatomical characters, the specimens are at best assigned to the cycadalean genus Pseudoctenis. This genus was f...
Michael Krings - One of the best experts on this subject based on the ideXlab platform.
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strobilus organization in the enigmatic gymnosperm bernettia inopinata from the jurassic of germany
Review of Palaeobotany and Palynology, 2016Co-Authors: Evelyn Kustatscher, Johanna H A Van Konijnenburgvan Cittert, Kathleen Bauer, Michael KringsAbstract:The enigmatic fossil Bernettia inopinata from Lower Jurassic strata of Upper Franconia, Germany, has been described as a leaf-like structure a leaf-like structure bearing a proximal cluster of densely spaced, pillow-like objects believed to represent ovules or ovule-containing units. The systematic affinities of B. inopinata have remained unresolved. This paper describes five strobili from Pechgraben near Bayreuth that show fertile units composed of B. inopinata and the delicate leaf-like structure Chlamydolepis lautneri in helical arrangement along a central axis. These fossils provide the first insights into the organization of the B. inopinata reproductive structure and demonstrate that B. inopinata and C. lautneri were produced by the same plant. Moreover, Desmiophyllum gothanii leaves closely associated with the strobili, together with specimens showing C. lautneri and the enigmatic microsporophyll Piroconites kuespertii in organic connection, support the hypothesis that these four taxa represent parts of the same plant. The genus Piroconites with its type-species P. kuespertii is validated. Although certain structural details of the B. inopinata plant are reminiscent of features seen in other gymnosperms, including Bennettitales (i.e. ovule structure, megasporophyll organization, microsporophyll organization), Gnetales (i.e. three-locular synangia, pollen, leaves), Glossopteridales (megasporophylls), and conifers (microsporophyll organization and arrangement), it does not fit well into any of the known groups of gymnosperms.
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reconstruction of a bennettitalean flower from the carnian upper triassic of lunz lower austria
Review of Palaeobotany and Palynology, 2010Co-Authors: Christian Pott, Michael Krings, Hans Kerp, Else Marie FriisAbstract:Abstract The Bennettitales are a Mesozoic group of gymnosperms with complex reproductive organs that figure prominently in hypotheses on the ancestry and origin of angiosperms. However, the exact phylogenetic position of the Bennettitales is still debated, due in part to the scarcity of conclusive fertile remains from the Triassic. In this study we reconstruct a bennettitalean flower from isolated parts from the Carnian (Upper Triassic) of Lunz in Lower Austria, including Cycadolepis wettsteinii scale leaves, Haitingeria krasseri pollen organs, and Bennetticarpus wettsteinii ovulate organs/seed cones, based on correspondences in gross morphology and epidermal anatomy. The flower has small pollen organs with spreading and well-exposed pollen sacs; pollen sacs are not organised in synangia, and the ovulate organ is characterised by a low number of relatively large seeds and a large number of interseminal scales in relation to ovules/seeds. The flower lacks several of the characteristic features seen in geologically younger bennettitaleans, including fused, inwardly curved pollen organs and large number of small seeds. The association of these isolated organs to a single flower provides a rare opportunity to assess the attribution of these early representative of the Bennettitales, and sheds new light on the evolutionary history and phylogenetic position of this ancient group of seed plants.
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The Carnian (Late Triassic) flora from Lunz in Lower Austria: Paleoecological considerations
Palaeoworld, 2008Co-Authors: Christian Pott, Michael Krings, Hans KerpAbstract:Abstract A recently completed systematic macromorphological and cuticular analysis of compressed gymnosperm foliage from the famous Carnian (Late Triassic) flora from Lunz in Lower Austria has provided detailed circumscriptions of the individual taxa and new information as to their ordinal and generic classification. Although the fossils represent several lineages of gymnosperms, including Cycadales, Bennettitales, Ginkgoales, it appeared that certain idiocuticular and epidermal features such as sunken stomata and papillate surfaces occur widespread among the taxa. The presence of coal seams indicates that the environmental conditions in the Lunz paleoecosystem were stable for longer periods and allowed for the accumulation of larger amounts of plant material. The formation of peat generally requires special conditions, including a stable, high groundwater table, reduced oxygen supply and low pH values, which are typically found in swamps or peat bogs. Many of the idiocuticular and epidermal features recorded for the Lunz plants can be interpreted as adaptations to ecological conditions characteristic of coal-producing peat swamps, e.g., physiological drought, and thus corroborate the interpretation of the Lunz paleoecosystem as a peat-forming environment.
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revision of the pterophyllum species cycadophytina Bennettitales in the carnian late triassic flora from lunz lower austria
Review of Palaeobotany and Palynology, 2007Co-Authors: Christian Pott, Hans Kerp, Johanna H A Van Konijnenburgvan Cittert, Michael KringsAbstract:Abstract A revision of the genus Pterophyllum in the famous Late Triassic flora of Lunz, Lower Austria, based on macromorphology, biometry, and epidermal anatomy is presented. Two distinct species, Pterophyllum filicoides and Pterophyllum brevipenne , are recognized. Other Pterophyllum “species” described from Lunz by D. Stur and F. Krasser in the late 19th and early 20th centuries are interpreted as conspecific with either of these two species; others represent cycadalean foliage assignable to the genus Nilssonia . Full-grown P. filicoides leaves are more than 45 cm long and oblong to broadly oval in outline; the lamina is subdivided into narrow leaf segments up to 11 cm long. Full-grown leaves of P. brevipenne are considerably smaller than those of P. filicoides , and lanceolate to spatulate in outline; the lamina is subdivided into leaf segments up to 2.7 cm long. Pterophyllum is by far the most common element in the Lunz flora. Moreover, the species from Lunz range among the earliest representatives of this genus in the fossil record. This suggests that certain Bennettitales locally became significant elements of the vegetation relatively early in their evolutionary history.
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first record of nilssoniopteris gymnospermophyta Bennettitales from the carnian upper triassic of lunz lower austria
Palaeontology, 2007Co-Authors: Christian Pott, Michael Krings, Hans KerpAbstract:Abstract: The Carnian (Late Triassic) flora of Lunz in Lower Austria is famous for an abundance of well-preserved bennettitalean and cycadalean foliage and reproductive structures. However, only the fertile remains have been studied in detail to date. Recently completed systematic macromorphological and cuticular analyses of leaf fossils from Lunz revealed that several forms previously accommodated in the genus Macrotaeniopteris do not represent ferns but rather Bennettitales assignable to the genus Nilssoniopteris. We describe three species of Nilssoniopteris, which represent the first records for this genus from Lunz, and one of the earliest accounts of Nilssoniopteris in the Northern Hemisphere. The following new combinations are introduced: Nilssoniopteris haidingeri (Stur ex Krasser, 1909a) comb. nov., N. angustior (Stur ex Krasser, 1909a) comb. nov. and N. lunzensis (Stur ex Krasser, 1909a) comb. nov. The discovery of Nilssoniopteris further substantiates the significance of the Lunz flora as one of the richest and most diverse early Late Triassic floras from the Northern Hemisphere.
Else Marie Friis - One of the best experts on this subject based on the ideXlab platform.
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welwitschioid diversity in the early cretaceous evidence from fossil seeds with pollen from portugal and eastern north america
Grana, 2014Co-Authors: Else Marie Friis, Kaj Raunsgaard Pedersen, Peter R. CraneAbstract:AbstractBicatia gen. et sp. nov. from the Early Cretaceous of the Northern Hemisphere is described based on three species of dispersed seeds: Bicatia costata from the Juncal and Famalicao localities (western Portugal) and the Kenilworth locality (eastern North America), B. juncalensis from the Juncal locality, and B. rugosa from the Puddledock locality (eastern North America). Seeds of B. costata and B. rugosa are known from both lignitised (Juncal, Kenilworth, Puddledock) and charcoalified specimens (Famalicao, Puddledock), whereas seeds of B. juncalensis are known only from lignitised material (Juncal). All three species have the same characteristic chlamydospermous organisation seen in the wide range of other Early Cretaceous seeds that have been assigned to the Bennettitales-Erdtmanithecales-Gnetales (BEG) group. However, the species of Bicatia differ from all previously described BEG seeds in having a disymmetrical and flattened seed envelope with more or less distinct lateral wings. All three specie...
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trichomes on the leaves of anomozamites villosus sp nov Bennettitales from the daohugou beds middle jurassic inner mongolia china mechanical defence against herbivorous arthropods
Review of Palaeobotany and Palynology, 2012Co-Authors: Christian Pott, Stephen Mcloughlin, Wu Shunqing, Else Marie FriisAbstract:The abaxial leaf surfaces of Anomozamites villosus sp. nov., a new species of bennettitalean foliage from the Middle Jurassic Daohugou beds of Inner Mongolia, China, are covered with soft, shaggy hairs that are loosely, but regularly distributed across the lamina. Selectively arranged, long, stiff or acerate hairs directed or bent towards the leaf apex, project on the abaxial side of the leaf from the rachis margins. Both types of hairs are interpreted predominantly as adaptations for passive defence against damage by arthropods (sap-sucking, leaf-chewing or oviposition) rather than being morphological responses to physical environmental parameters, e.g. xeromorphic features. As several of the leaves show evidence for high levels of leaf-margin feeding by phytophagous arthropods, these mechanisms have not been entirely effective and may have evolved to defend against only selected arthropods or behavioural strategies. These findings contribute to the reconstruction of ecological interactions in the exceptionally preserved Jurassic Daohugou biota of northern China, and provide a rare insight into the plant–arthropod co-evolutionary ‘arms race’.
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reconstruction of a bennettitalean flower from the carnian upper triassic of lunz lower austria
Review of Palaeobotany and Palynology, 2010Co-Authors: Christian Pott, Michael Krings, Hans Kerp, Else Marie FriisAbstract:Abstract The Bennettitales are a Mesozoic group of gymnosperms with complex reproductive organs that figure prominently in hypotheses on the ancestry and origin of angiosperms. However, the exact phylogenetic position of the Bennettitales is still debated, due in part to the scarcity of conclusive fertile remains from the Triassic. In this study we reconstruct a bennettitalean flower from isolated parts from the Carnian (Upper Triassic) of Lunz in Lower Austria, including Cycadolepis wettsteinii scale leaves, Haitingeria krasseri pollen organs, and Bennetticarpus wettsteinii ovulate organs/seed cones, based on correspondences in gross morphology and epidermal anatomy. The flower has small pollen organs with spreading and well-exposed pollen sacs; pollen sacs are not organised in synangia, and the ovulate organ is characterised by a low number of relatively large seeds and a large number of interseminal scales in relation to ovules/seeds. The flower lacks several of the characteristic features seen in geologically younger bennettitaleans, including fused, inwardly curved pollen organs and large number of small seeds. The association of these isolated organs to a single flower provides a rare opportunity to assess the attribution of these early representative of the Bennettitales, and sheds new light on the evolutionary history and phylogenetic position of this ancient group of seed plants.
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Early Cretaceous mesofossils from Portugal and eastern North America related to the Bennettitales-Erdtmanithecales-Gnetales group
American Journal of Botany, 2009Co-Authors: Else Marie Friis, Kaj Raunsgaard Pedersen, Peter R. CraneAbstract:Four new genera and six new species of fossil seed (Buarcospermum tetragonium, Lignierispermum maroneae, Lobospermum glabrum, L. rugosum, L. stampanonii, Rugonella trigonospermum) are described from five Early Cretaceous mesofossil floras from Portugal and eastern North America. The four genera are distinguished by differences in size, shape, and details of seed anatomy, but all are unusual in having an outer seed envelope with a distinctive anatomical structure that surrounds the nucellus and the integument. The integument is extended apically into a long, narrow micropylar tube. The four new genera are part of a diverse, but previously unrecognized, complex of extinct plants that was widespread in Early Cretaceous vegetation and that coexisted in similar habitats with early angiosperms. The distinctive structure of these seeds, and the strong similarities to other fossil seeds (Ephedra, Ephedripites, Erdtmanispermum, Raunsgaardispermum, and some Bennettitales) already known from the Early Cretaceous, suggests that this newly recognized complex of extinct plants, together with Bennettitales, Erdtmanithecales, and Gnetales (the BEG group), is phylogenetically closely related.
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raunsgaardispermum lusitanicum gen et sp nov a new seed with in situ pollen from the early cretaceous probably berriasian of portugal further support for the Bennettitales erdtmanithecales gnetales link
Grana, 2008Co-Authors: Mario Miguel Mendes, Joao Pais, Else Marie FriisAbstract:A new genus and species, Raunsgaardispermum lusitanicum, is described from the Bombarral formation, Early Cretaceous (probably Berriasian) of Portugal. The new taxon is based on small well‐preserved, lignitised seeds, about 1.2 – 2.1 mm long and 0.9 – 1.26 mm wide, ovoid to broadly elliptic in outline with a distinct pointed micropylar region. The seed wall is composed by a thin membranous integument extended apically into a long tubular micropyle. The integument is enclosed almost completely by an outer envelope except for a small circular opening for micropylar region. The outer envelope is bivalved and sclerenchymatous, ornamented by narrow longitudinal ridges. Papillae are present apically on the inner surface of the seed envelope adjacent to the micropylar tube. Monocolpate, tectate‐psilate‐punctate pollen grains, about 26 – 29 µm long and 14 – 16 µm wide, were observed in situ in the micropyle of one seed and on the outer surface of several others. The seeds show an interesting character combination...
Thomas N. Taylor - One of the best experts on this subject based on the ideXlab platform.
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Secondary phloem anatomy of Cycadeoidea (Bennettitales).
American journal of botany, 2007Co-Authors: Patricia E. Ryberg, Edith L Taylor, Thomas N. TaylorAbstract:Secondary phloem anatomy of several species of Cycadeoidea is described from trunks in the Wieland Collection, Peabody Museum of Natural History. The trunks were collected from the Lakota Formation, Lower Cretaceous, Black Hills of South Dakota. Secondary phloem is extensively developed and consists of alternating, tangential bands of fibers and sieve elements, with rare phloem parenchyma. Uniseriate rays, 2-22 cells high, occur between every one to three files of the axial system. Fibers are long, more than 1200 μm, approximately 26.6-34.2 μm in diameter, and have slit-like apertures on the lateral walls. Sieve elements range from 16-25 μm in diameter and are up to 500 μm long. Elliptical sieve areas appear on both end and radial walls and measure 10 μm across; minute spots, which may represent sieve pores, are present within the sieve areas. Secondary phloem of North American Cycadeoidea is similar in organization (alternating tangential bands) and cell types (sieve cells, fibers, axial parenchyma) to that known in other extant and fossil cycadophytes and some seed ferns. The unusual pattern of cell types and thickness of secondary phloem is discussed in the context of plant habit, phloem efficiency, and potential phylogenetic importance.
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anatomically preserved leaves of the conifer notophytum krauselii podocarpaceae from the triassic of antarctica
American Journal of Botany, 1998Co-Authors: Brian J Axsmith, Thomas N. Taylor, Edith L TaylorAbstract:Permineralized leaves of the Triassic podocarpaceous conifer Notophytum krauselii are described from the Fremouw Formation of Antarctica. The leaves are elongate and apetiolate with 8‐12 parallel veins. The adaxial epidermis consists of rows of rectangular to pentagonal cells; the abaxial epidermis is papillate. Longitudinally oriented stomata occur on both surfaces. An adaxial palisade layer is present and auxiliary sclereids are common in the mesophyll. The vascular bundles have a weakly defined sheath and are flanked by transfusion tracheids. Bundles in the basipetal area of the leaf are capped by sclerotic tissue and subtended by resin canals. These leaves are superficially similar to those of the extant podocarp genus Nageia, but probably represent a distinct acquisition of this leaf type within the Podocarpaceae. Notophytum leaves are similar to the common compression fossil Heidiphyllum elongatum and may be closely related or even conspecific. Evidence from Antarctica suggests that Heidiphyllum and the seed cone Telemachus were produced by the same plant, and may be closely related to several other early Mesozoic conifers with multiveined leaves. With the exception of permineralized and petrified wood, anatomically preserved plant fossils from the Triassic are exceedingly rare. This is unfortunate since it is widely accepted, based on the impression-compression fossil record, that the Triassic was a pivotal time in seed plant evolution. Some of the more dramatic examples of Triassic evolutionary radiations include the Bennettitales, the pteridosperm order Corystospermales, and the conifers. To date, the silicified peat deposits of the Fremouw Formation in Antarctica remain the only significant source of abundant, anatomically preserved Triassic plant fossils (Taylor, Taylor, and Collinson, 1989). Meyer-Berthaud and Taylor (1991) described Notophytum krauselii, a conifer stem with probable podocarpaceous affinities, from the silicified peat of Fremouw Peak. Leaf bases were well preserved. However, the distal parts of the leaf were represented only by short straps of tissue with poor internal preservation. Specimens with better preservation have recently been recognized, which demonstrate that the leaves of Notophytumwere elongate with up to 12 parallel veins, and are morphologically similar to the impression-compression taxon Heidiphyllum elongatus (Anderson, 1978). This is of particular significance since Heidiphyllum is among the most common Gondwanan Triassic fossil seed plants (Anderson and Anderson, 1983). In this paper we describe the leaves of Notophytum and consider the implications of this leaf type in understanding the early evolutionary history of the Podocarpaceae. We also provide the first information on Heidiphyllum cuticles from Antarctica, and present additional evidence suggesting that Heidiphyllum elonga
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pollen morphology and ultrastructure of the Bennettitales in situ pollen of cycadeoidea
American Journal of Botany, 1995Co-Authors: Thomas N. Taylor, Jeffrey M OsbornAbstract:boundary, and a thicker granular infratectum. The infratectal granules are relatively uniform in size, however, variation occurs in the arrangement of granules. In some grains, the sexine appears homogeneous because there is little lacunal space between the individual granules. The granular infratectum is in direct contact with the underlying nexine. The nexine is uniform in thickness in both apertural and nonapertural regions, and it lacks lamellae throughout. Pollen morphology and ultrastructure are compared with those of the bennettitalean genus Leguminanthus and the dispersed genus Monosulcites. In addition, the fine structure of Cycadeoidea pollen is compared to that ofthe gymnosperm groups with which the Bennettitales are regarded to be most closely related, including Gnetales, Pentoxylales, and Eucommiidites-type pollen-producing plants.