Publications by authors named "Margaret E Collinson"

19 Publications

  • Page 1 of 1

Fruit Morphology and Anatomy of the Spondioid Anacardiaceae.

Bot Rev 2018 3;84(4):315-393. Epub 2018 Aug 3.

5Florida Museum of Natural History, University of Florida, Gainesville, FL USA.

The Spondioideae subfamily of the Anacardiaceae is widely distributed today in tropical regions. Recent molecular phylogenetic investigations indicate that the Spondioideae are not monophyletic, but rather comprise at least two separate clades that are difficult to distinguish using vegetative and floral characters. Nevertheless, the syndrome of fruit characters traditionally used in identifying the subfamily is useful in discriminating genera of these clades and for identification of both modern and fossil anacardiaceous fruits. Here we document the morphology and anatomy of endocarps for representatives of all extant genera traditionally treated as Spondioideae, plus two genera that have been placed close to them in molecular investigations, and . All genera are characterized by drupe-like fruits with sclerified stones that vary from uni- to multilocular depending on the genus. Germination modes vary throughout the Spondioideae. Some have characteristic plug-like opercula; others have recessed bilabiate germination valves, and still others open by apical flaps or simple slits. Although most currently recognized genera appear to be monophyletic, fruit morphology indicates that current circumscriptions of , and are in need of revision.
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http://dx.doi.org/10.1007/s12229-018-9201-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6223893PMC
August 2018

Species diversity driven by morphological and ecological disparity: a case study of comparative seed morphology and anatomy across a large monocot order.

AoB Plants 2016 27;8. Epub 2016 Oct 27.

Swiss Light Source, Paul Scherrer Institut, 5232 Villigen PSI, Switzerland.

Phenotypic variation can be attributed to genetic heritability as well as biotic and abiotic factors. Across Zingiberales, there is a high variation in the number of species per clade and in phenotypic diversity. Factors contributing to this phenotypic variation have never been studied in a phylogenetic or ecological context. Seeds of 166 species from all eight families in Zingiberales were analyzed for 51 characters using synchrotron based 3D X-ray tomographic microscopy to determine phylogenetically informative characters and to understand the distribution of morphological disparity within the order. All families are distinguishable based on seed characters. Non-metric multidimensional scaling analyses show Zingiberaceae occupy the largest seed morphospace relative to the other families, and environmental analyses demonstrate that Zingiberaceae inhabit both temperate and tropical regions, while other Zingiberales are almost exclusively tropical. Temperate species do not cluster in morphospace nor do they share a common suite of character states. This suggests that the diversity seen is not driven by adaptation to temperate niches; rather, the morphological disparity seen likely reflects an underlying genetic plasticity that allowed Zingiberaceae to repeatedly colonize temperate environments. The notable morphoanatomical variety in Zingiberaceae seeds may account for their extraordinary ecological success and high species diversity as compared to other Zingiberales.
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http://dx.doi.org/10.1093/aobpla/plw063DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5091906PMC
October 2016

X-rays and virtual taphonomy resolve the first Cissus (Vitaceae) macrofossils from Africa as early-diverging members of the genus.

Am J Bot 2016 09 19;103(9):1657-77. Epub 2016 Sep 19.

Imaging and Analysis Centre, Natural History Museum, London, SW7 5BD, UK.

Premise Of The Study: Fossilized seeds similar to Cissus (Vitaceae) have been recognized from the Miocene of Kenya, though some were previously assigned to the Menispermaceae. We undertook a comparative survey of extant African Cissus seeds to identify the fossils and consider their implications for the evolution and biogeography of Cissus and for African early Miocene paleoenvironments.

Methods: Micro-computed tomography (µCT) and synchrotron-based X-ray tomographic microscopy (SRXTM) were used to study seed morphology and anatomy. Virtual taphonomy, using SRXTM data sets, produced digital fossils to elucidate seed taphonomy. Phylogenetic relationships within Cissus were reconstructed using existing and newly produced DNA sequences for African species. Paleobiology and paleoecology were inferred from African nearest living relatives.

Key Results: The fossils were assigned to four new Cissus species, related to four modern clades. The fossil plants were interpreted as climbers inhabiting a mosaic of riverine woodland and forest to more open habitats. Virtual taphonomy explained how complex mineral infill processes concealed key seed features, causing the previous taxonomic misidentification. Newly sampled African species, with seeds most similar to the fossils, belong to four clades within core Cissus, two of which are early diverging.

Conclusions: Virtual taphonomy, combined with X-ray imaging, has enabled recognition of the first fossil Cissus and Vitaceae from Africa. Early-divergent members of the core Cissus clade were present in Africa by at least the early Miocene, with an African origin suggested for the Cissus sciaphila clade. The fossils provide supporting evidence for mosaic paleoenvironments inhabited by early Miocene hominoids.
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http://dx.doi.org/10.3732/ajb.1600177DOI Listing
September 2016

Seed morphology and anatomy and its utility in recognizing subfamilies and tribes of Zingiberaceae.

Am J Bot 2015 Nov 27;102(11):1814-41. Epub 2015 Oct 27.

Advanced Light Source, Lawrence Berkeley National Laboratories, Berkeley, California 94720 USA.

Premise Of The Study: Recent phylogenetic analyses based on molecular data suggested that the monocot family Zingiberaceae be separated into four subfamilies and four tribes. Robust morphological characters to support these clades are lacking. Seeds were analyzed in a phylogenetic context to test independently the circumscription of clades and to better understand evolution of seed characters within Zingiberaceae.

Methods: Seventy-five species from three of the four subfamilies were analyzed using synchrotron based x-ray tomographic microscopy (SRXTM) and scored for 39 morphoanatomical characters.

Key Results: Zingiberaceae seeds are some of the most structurally complex seeds in angiosperms. No single seed character was found to distinguish each subfamily, but combinations of characters were found to differentiate between the subfamilies. Recognition of the tribes based on seeds was possible for Globbeae, but not for Alpinieae, Riedelieae, or Zingibereae, due to considerable variation.

Conclusions: SRXTM is an excellent, nondestructive tool to capture morphoanatomical variation of seeds and allows for the study of taxa with limited material available. Alpinioideae, Siphonochiloideae, Tamijioideae, and Zingiberoideae are well supported based on both molecular and morphological data, including multiple seed characters. Globbeae are well supported as a distinctive tribe within the Zingiberoideae, but no other tribe could be differentiated using seeds due to considerable homoplasy when compared with currently accepted relationships based on molecular data. Novel seed characters suggest tribal affinities for two currently unplaced Zingiberaceae taxa: Siliquamomum may be related to Riedelieae and Monolophus to Zingibereae, but further work is needed before formal revision of the family.
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http://dx.doi.org/10.3732/ajb.1500300DOI Listing
November 2015

Terrestrial cooling in Northern Europe during the eocene-oligocene transition.

Proc Natl Acad Sci U S A 2013 May 22;110(19):7562-7. Epub 2013 Apr 22.

Department of Chemistry and Center for Integrative Geoscience, University of Connecticut, Storrs, CT 06269, USA.

Geochemical and modeling studies suggest that the transition from the "greenhouse" state of the Late Eocene to the "icehouse" conditions of the Oligocene 34-33.5 Ma was triggered by a reduction of atmospheric pCO2 that enabled the rapid buildup of a permanent ice sheet on the Antarctic continent. Marine records show that the drop in pCO2 during this interval was accompanied by a significant decline in high-latitude sea surface and deep ocean temperature and enhanced seasonality in middle and high latitudes. However, terrestrial records of this climate transition show heterogeneous responses to changing pCO2 and ocean temperatures, with some records showing a significant time lag in the temperature response to declining pCO2. We measured the Δ47 of aragonite shells of the freshwater gastropod Viviparus lentus from the Solent Group, Hampshire Basin, United Kingdom, to reconstruct terrestrial temperature and hydrologic change in the North Atlantic region during the Eocene-Oligocene transition. Our data show a decrease in growing-season surface water temperatures (~10 °C) during the Eocene-Oligocene transition, corresponding to an average decrease in mean annual air temperature of ~4-6 °C from the Late Eocene to Early Oligocene. The magnitude of cooling is similar to observed decreases in North Atlantic sea surface temperature over this interval and occurs during major glacial expansion. This suggests a close linkage between atmospheric carbon dioxide concentrations, Northern Hemisphere temperature, and expansion of the Antarctic ice sheets.
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http://dx.doi.org/10.1073/pnas.1210930110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3651463PMC
May 2013

Inconsistent redefining of the carbon spherule "impact" proxy.

Proc Natl Acad Sci U S A 2012 Aug 24;109(34):E2244; author reply E2245-7. Epub 2012 Jul 24.

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http://dx.doi.org/10.1073/pnas.1206108109DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3427080PMC
August 2012

Ancient fig wasps indicate at least 34 Myr of stasis in their mutualism with fig trees.

Biol Lett 2010 Dec 16;6(6):838-42. Epub 2010 Jun 16.

University of Leeds, UK.

Fig wasps and fig trees are mutually dependent, with each of the 800 or so species of fig trees (Ficus, Moraceae) typically pollinated by a single species of fig wasp (Hymenoptera: Agaonidae). Molecular evidence suggests that the relationship existed over 65 Ma, during the Cretaceous. Here, we record the discovery of the oldest known fossil fig wasps, from England, dated at 34 Ma. They possess pollen pockets that contain fossil Ficus pollen. The length of their ovipositors indicates that their host trees had a dioecious breeding system. Confocal microscopy and scanning electron microscopy reveal that the fossil female fig wasps, and more recent species from Miocene Dominican amber, display the same suite of anatomical characters associated with fig entry and pollen-carrying as modern species. The pollen is also typical of modern Ficus. No innovations in the relationship are discernible for the last tens of millions of years.
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http://dx.doi.org/10.1098/rsbl.2010.0389DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3001375PMC
December 2010

Seed fertilization, development, and germination in Hydatellaceae (Nymphaeales): Implications for endosperm evolution in early angiosperms.

Am J Bot 2009 Sep 13;96(9):1581-93. Epub 2009 Aug 13.

Royal Botanic Gardens, Kew, Richmond, Surrey TW9 3AB, UK.

New data on endosperm development in the early-divergent angiosperm Trithuria (Hydatellaceae) indicate that double fertilization results in formation of cellularized micropylar and unicellular chalazal domains with contrasting ontogenetic trajectories, as in waterlilies. The micropylar domain ultimately forms the cellular endosperm in the dispersed seed. The chalazal domain forms a single-celled haustorium with a large nucleus; this haustorium ultimately degenerates to form a space in the dispersed seed, similar to the chalazal endosperm haustorium of waterlilies. The endosperm condition in Trithuria and waterlilies resembles the helobial condition that characterizes some monocots, but contrasts with Amborella and Illicium, in which most of the mature endosperm is formed from the chalazal domain. The precise location of the primary endosperm nucleus governs the relative sizes of the chalazal and micropylar domains, but not their subsequent developmental trajectories. The unusual tissue layer surrounding the bilobed cotyledonary sheath in seedlings of some species of Trithuria is a belt of persistent endosperm, comparable with that of some other early-divergent angiosperms with a well-developed perisperm, such as Saururaceae and Piperaceae. The endosperm of Trithuria is limited in size and storage capacity but relatively persistent.
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http://dx.doi.org/10.3732/ajb.0900033DOI Listing
September 2009

Experimental determination of a Viviparus contectus thermometry equation.

Rapid Commun Mass Spectrom 2009 Sep;23(18):2939-51

School of Earth, Ocean & Environmental Sciences, University of Plymouth, Drake Circus, Plymouth PL4 8AA, UK.

Experimental measurements of the (18)O/(16)O isotope fractionation between the biogenic aragonite of Viviparus contectus (Gastropoda) and its host freshwater were undertaken to generate a species-specific thermometry equation. The temperature dependence of the fractionation factor and the relationship between Deltadelta(18)O (delta(18)O(carb.) - delta(18)O(water)) and temperature were calculated from specimens maintained under laboratory and field (collection and cage) conditions. The field specimens were grown (Somerset, UK) between August 2007 and August 2008, with water samples and temperature measurements taken monthly. Specimens grown in the laboratory experiment were maintained under constant temperatures (15 degrees C, 20 degrees C and 25 degrees C) with water samples collected weekly. Application of a linear regression to the datasets indicated that the gradients of all three experiments were within experimental error of each other (+/-2 times the standard error); therefore, a combined (laboratory and field data) correlation could be applied. The relationship between Deltadelta(18)O (delta(18)O(carb.) - delta(18)O(water)) and temperature (T) for this combined dataset is given by: T = - 7.43( + 0.87, - 1.13)*Deltadelta18O + 22.89(+/- 2.09) (T is in degrees C, delta(18)O(carb.) is with respect to Vienna Pee Dee Belemnite (VPDB) and delta(18)O(water) is with respect to Vienna Standard Mean Ocean Water (VSMOW). Quoted errors are 2 times standard error).Comparisons made with existing aragonitic thermometry equations reveal that the linear regression for the combined Viviparus contectus equation is within 2 times the standard error of previously reported aragonitic thermometry equations. This suggests there are no species-specific vital effects for Viviparus contectus. Seasonal delta(18)O(carb.) profiles from specimens retrieved from the field cage experiment indicate that during shell secretion the delta(18)O(carb.) of the shell carbonate is not influenced by size, sex or whether females contained eggs or juveniles.
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http://dx.doi.org/10.1002/rcm.4203DOI Listing
September 2009

Elucidating the affinities and habitat of ancient, widespread Cyperaceae: Volkeria messelensis gen. et sp. nov., a fossil mapanioid sedge from the Eocene of Europe.

Am J Bot 2009 Aug 20;96(8):1506-18. Epub 2009 Jul 20.

Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK.

The sedges (family Cyperaceae) are an economically and ecologically important monocot group dating back at least to the Paleocene. While modern genera are mostly unknown before the Oligocene, several extinct taxa are recognized as the earliest sedges. Their affinities have been unclear until now, because they are found as isolated, often abraded fruits or endocarps. Exceptionally preserved sedge fossils from the Middle Eocene of Messel, Germany yield more characters for identification. Fossil cyperacean infructescences with in situ pollen are recognized for the first time and show features of the early-divergent mapanioid sedges. Pollen resembles that of tribe Hypolytreae. Comparisons with extant taxa suggest the closest affinities with Hypolytrum and Mapania. However, the Messel fossils represent a distinct taxon, Volkeria messelensis gen. et sp. nov. Without the additional characters of infructescence and pollen, the Messel fruits would have been placed in the extinct genus Caricoidea, a typical Eocene sedge that was widespread across Eurasia. Similarities of fruit structure suggest that Caricoidea was also a mapanioid sedge. Mapanioid sedges are found today in tropical wet forests and swamps, a distribution suggesting that early sedges occupied a similar habitat, unlike many modern sedges, and were not precursors to open grassland vegetation.
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http://dx.doi.org/10.3732/ajb.0800427DOI Listing
August 2009

Taphonomy of the early Miocene flora, Hiwegi Formation, Rusinga Island, Kenya.

J Hum Evol 2009 Aug 3;57(2):149-62. Epub 2009 Jul 3.

Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 ORB, UK.

A fossil flora was collected in situ from early Miocene deposits at site R117 in the Hiwegi Formation of Rusinga Island contemporaneous with and in close proximity to the sites from where the anthropoid primates were recovered. The flora exhibits a spatially and temporally patchy distribution of fruits and seeds, mixed with twigs of various sizes, fragments of wood, bark, and leaves, all with random orientations and very low depositional dips. There has been minimal transport and the flora evidently accumulated as in situ litter beneath local vegetation. Based on Nearest Living Relatives (NLR) of fruits and seeds, the vegetation represented is a deciduous broad-leaved woodland with continuous canopy, with trees, shrubs, lianas, and climbers, reminiscent of the structure of the modern vegetation in the steep-sided protected valleys in the Laetoli-Endulen area. The interpretation of the vegetation is supported by the presence of twigs, wood, and bark fragments from larger diameter axes. Climbers are represented by twining stem fragments as well as by a wide variety of distinctive fruits and seeds. The proportion of fossilised thorny twigs represents only 3% of the twig collections, and there are no unequivocal forest trees amongst the NLR. No grasses were present; monocotyledons are only represented by a single date palm stone. No conifer seeds or cones have been recovered, and there are no coniferous leafy shoots.
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http://dx.doi.org/10.1016/j.jhevol.2009.02.010DOI Listing
August 2009

Virtual taphonomy using synchrotron tomographic microscopy reveals cryptic features and internal structure of modern and fossil plants.

Proc Natl Acad Sci U S A 2009 Jul 2;106(29):12013-8. Epub 2009 Jul 2.

Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, United Kingdom.

While more commonly applied in zoology, synchrotron radiation X-ray tomographic microscopy (SRXTM) is well-suited to nondestructive study of the morphology and anatomy of both fossil and modern plants. SRXTM uses hard X-rays and a monochromatic light source to provide high-resolution data with little beam-hardening, resulting in slice data with clear boundaries between materials. Anatomy is readily visualized, including various planes of section from a single specimen, as clear as in traditional histological sectioning at low magnifications. Thus, digital sectioning of rare or difficult material is possible. Differential X-ray attenuation allows visualization of different layers or chemistries to enable virtual 3-dimensional (3D) dissections of material. Virtual potential fossils can be visualized and digital tissue removal reveals cryptic underlying morphology. This is essential for fossil identification and for comparisons between assemblages where fossils are preserved by different means. SRXTM is a powerful approach for botanical studies using morphology and anatomy. The ability to gain search images in both 2D and 3D for potential fossils gives paleobotanists a tool--virtual taphonomy--to improve our understanding of plant evolution and paleobiogeography.
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http://dx.doi.org/10.1073/pnas.0901468106DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2715531PMC
July 2009

Scanning electron microscopy and synchrotron radiation x-ray tomographic microscopy of 330 million year old charcoalified seed fern fertile organs.

Microsc Microanal 2009 Apr;15(2):166-73

Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW200EX, UK.

Abundant charcoalified seed fern (pteridosperm) pollen organs and ovules have been recovered from Late Viséan (Mississippian 330 Ma) limestones from Kingswood, Fife, Scotland. To overcome limitations of data collection from these tiny, sometimes unique, fossils, we have combined low vacuum scanning electron microscopy on uncoated specimens with backscatter detector and synchrotron radiation X-ray tomographic microscopy utilizing the Materials Science and TOMCAT beamlines at the Swiss Light Source of the Paul Scherrer Institut. In combination these techniques improve upon traditional cellulose acetate peel sectioning because they enable study of external morphology and internal anatomy in multiple planes of section on a single specimen that is retained intact. The pollen organ Melissiotheca shows a basal parenchymatous cushion bearing more than 100 sporangia on the distal face. Digital sections show the occurrence of pollen in some sporangia. The described ovule is new and has eight integumentary lobes that are covered in spirally arranged glandular hairs. Virtual longitudinal sections reveal the lobes are free above the pollen chamber. Results are applied in taxonomy and will subsequently contribute to our understanding of the former diversity and evolution of ovules, seeds, and pollen organs in the seed ferns, the first seed-bearing plants to conquer the land.
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http://dx.doi.org/10.1017/S1431927609090126DOI Listing
April 2009

Geochemical evidence for combustion of hydrocarbons during the K-T impact event.

Proc Natl Acad Sci U S A 2009 Mar 26;106(11):4112-7. Epub 2009 Feb 26.

Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, United Kingdom.

It has been proposed that extensive wildfires occurred after the Cretaceous-Tertiary (K-T) impact event. An abundance of soot and pyrosynthetic polycyclic aromatic hydrocarbons (pPAHs) in marine K-T boundary impact rocks (BIRs) have been considered support for this hypothesis. However, nonmarine K-T BIRs, from across North America, contain only rare occurrences of charcoal yet abundant noncharred plant remains. pPAHs and soot can be formed from a variety of sources, including partial combustion of vegetation and hydrocarbons whereby modern pPAH signatures are traceable to their source. We present results from multiple nonmarine K-T boundary sites from North America and reveal that the K-T BIRs have a pPAH signature consistent with the combustion of hydrocarbons and not living plant biomass, providing further evidence against K-T wildfires and compelling evidence that a significant volume of hydrocarbons was combusted during the K-T impact event.
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http://dx.doi.org/10.1073/pnas.0813117106DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2657452PMC
March 2009

Fossil cyclanthus (cyclanthaceae, pandanales) from the eocene of Germany and England.

Am J Bot 2008 Jun;95(6):688-99

Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK.

The first known fossil fruits and seeds of Cyclanthaceae are described here. Cyclanthus messelensis sp. nov., from the Middle Eocene of Messel, Germany, has discoidal fruiting cycles up to 6 cm in diameter, with a central hole, radiating fiber strands, a thickened outer rim, and paratetracytic stomata. In situ seeds are up to 2 mm long, with an elongate micropylar end, a chalazal neck, and adpressed bands. The Messel fruits and seeds are nearly identical to those of Cyclanthus, differing in minor details of cuticular structure and seeds. The exceptional preservation at Messel (including in situ and isolated seeds) has also allowed us to establish the taxonomic affinity of isolated seeds ('Scirpus' lakensis) that are spatially and temporally widespread in the late Early and early Middle Eocene of southern England. Cyclanthus lakensis comb. nov. is described here as a morphotaxon for isolated fossil Cyclanthus seeds, preserved only as cuticular envelopes. Cyclanthus is another example of links between Eocene Europe and Recent South American floras because it is found today only from Mexico to South America. This material represents the first fossil fruits and seeds of Cyclanthus, which clearly was once growing in the Paleogene of the Old World.
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http://dx.doi.org/10.3732/ajb.2007390DOI Listing
June 2008

Increased terrestrial methane cycling at the Palaeocene-Eocene thermal maximum.

Nature 2007 Sep;449(7160):332-5

Organic Geochemistry Unit, Bristol Biogeochemistry Research Centre, School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK.

The Palaeocene-Eocene thermal maximum (PETM), a period of intense, global warming about 55 million years ago, has been attributed to a rapid rise in greenhouse gas levels, with dissociation of methane hydrates being the most commonly invoked explanation. It has been suggested previously that high-latitude methane emissions from terrestrial environments could have enhanced the warming effect, but direct evidence for an increased methane flux from wetlands is lacking. The Cobham Lignite, a recently characterized expanded lacustrine/mire deposit in England, spans the onset of the PETM and therefore provides an opportunity to examine the biogeochemical response of wetland-type ecosystems at that time. Here we report the occurrence of hopanoids, biomarkers derived from bacteria, in the mire sediments from Cobham. We measure a decrease in the carbon isotope values of the hopanoids at the onset of the PETM interval, which suggests an increase in the methanotroph population. We propose that this reflects an increase in methane production potentially driven by changes to a warmer and wetter climate. Our data suggest that the release of methane from the terrestrial biosphere increased and possibly acted as a positive feedback mechanism to global warming.
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http://dx.doi.org/10.1038/nature06012DOI Listing
September 2007

Episodic fresh surface waters in the Eocene Arctic Ocean.

Nature 2006 Jun;441(7093):606-9

Palaeoecology, Institute of Environmental Biology, Utrecht University, Laboratory of Palaeobotany and Palynology, Budapestlaan 4, 3584 CD Utrecht, The Netherlands.

It has been suggested, on the basis of modern hydrology and fully coupled palaeoclimate simulations, that the warm greenhouse conditions that characterized the early Palaeogene period (55-45 Myr ago) probably induced an intensified hydrological cycle with precipitation exceeding evaporation at high latitudes. Little field evidence, however, has been available to constrain oceanic conditions in the Arctic during this period. Here we analyse Palaeogene sediments obtained during the Arctic Coring Expedition, showing that large quantities of the free-floating fern Azolla grew and reproduced in the Arctic Ocean by the onset of the middle Eocene epoch (approximately 50 Myr ago). The Azolla and accompanying abundant freshwater organic and siliceous microfossils indicate an episodic freshening of Arctic surface waters during an approximately 800,000-year interval. The abundant remains of Azolla that characterize basal middle Eocene marine deposits of all Nordic seas probably represent transported assemblages resulting from freshwater spills from the Arctic Ocean that reached as far south as the North Sea. The termination of the Azolla phase in the Arctic coincides with a local sea surface temperature rise from approximately 10 degrees C to 13 degrees C, pointing to simultaneous increases in salt and heat supply owing to the influx of waters from adjacent oceans. We suggest that onset and termination of the Azolla phase depended on the degree of oceanic exchange between Arctic Ocean and adjacent seas.
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http://dx.doi.org/10.1038/nature04692DOI Listing
June 2006

Environmental mutagenesis during the end-Permian ecological crisis.

Proc Natl Acad Sci U S A 2004 Aug 28;101(35):12952-6. Epub 2004 Jul 28.

Laboratory of Palaeobotany and Palynology, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands.

During the end-Permian ecological crisis, terrestrial ecosystems experienced preferential dieback of woody vegetation. Across the world, surviving herbaceous lycopsids played a pioneering role in repopulating deforested terrain. We document that the microspores of these lycopsids were regularly released in unseparated tetrads indicative of failure to complete the normal process of spore development. Although involvement of mutation has long been hinted at or proposed in theory, this finding provides concrete evidence for chronic environmental mutagenesis at the time of global ecological crisis. Prolonged exposure to enhanced UV radiation could account satisfactorily for a worldwide increase in land plant mutation. At the end of the Permian, a period of raised UV stress may have been the consequence of severe disruption of the stratospheric ozone balance by excessive emission of hydrothermal organohalogens in the vast area of Siberian Traps volcanism.
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http://dx.doi.org/10.1073/pnas.0404472101DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC516500PMC
August 2004

Eucommia (Eucommiaceae), a potential biothermometer for the reconstruction of paleoenvironments.

Am J Bot 2003 Jan;90(1):1-7

Department of Paleobotany, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China;

The living trees of Eucommia ulmoides, an endemic species in China, grow from 200 to 1700 m above sea level, within the geographic range from 102° E to 118° E and from 25° N to 35° N. Spring temperatures in these regions vary from 12.3°C to 20.1°C. A physiological study (using germination tests) of E. ulmoides has been undertaken to test the role of spring temperature as a factor controlling the distribution of Eucommia. Results show that the spring temperature is a limiting factor for Eucommia seed germination and hence for the distribution pattern of the genus. The suitable range of temperature for seed germination, established experimentally, is from 13°C to 22°C, with an optimum of 18°C. Specimens of fossil Eucommia cf. ulmoides, preserved as a branch segment and leaves, showing the distinctive latex, were found in Middle Miocene sediments of Shanwang Formation, Shandong Province, East China. If the climatic tolerances documented here for E. ulmoides are extrapolated to Shanwang, they are in fact consistent with other predictions of the paleoclimate at this site, indicative of the potential value of Eucommia as a biothermometer. These Miocene fossils, and one previously described Eocene fruit specimen, prove the former existence of Eucommia in China in addition to North America and Europe. This confirms that the genus is not a recent arrival in China and extends our understanding of the past biogeography of the genus.
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http://dx.doi.org/10.3732/ajb.90.1.1DOI Listing
January 2003