Showing papers by "Margaret E. Collinson published in 2004"
TL;DR: It is document that the microspores of these lycopsids were regularly released in unseparated tetrads indicative of failure to complete the normal process of spore development, providing concrete evidence for chronic environmental mutagenesis at the time of global ecological crisis.
Abstract: 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.
227 citations
TL;DR: A new high-resolution, c 1 Ma mammalian record in continental Eocene-Oligocene strata in the Hampshire Basin was used to investigate the nature and timing of the major Europe-wide mammalian faunal turnover termed the Grande Coupure as mentioned in this paper.
Abstract: A new high-resolution, c 1 Ma mammalian record in continental Eocene–Oligocene strata in the Hampshire Basin is used to investigate the nature and timing of the major Europe-wide mammalian faunal turnover termed the Grande Coupure Whether this was caused by climate change or by competition with taxa dispersing from Asia is controversial The mammalian faunas in this record, after rarefaction analysis, show a sharp reduction in diversity only after the Grande Coupure Improved correlation of NW European successions to global events confirms the Grande Coupure as earliest Oligocene It shows that a c 350 ka hiatus interrupts the Hampshire and Paris Basin sequences prior to the first record of post-Grande Coupure Asian taxa Hiatus-bridging faunas from elsewhere in Europe record mainly post-Grande Coupure taxa, suggesting that the turnover occurred early in the hiatus, minimizing bias to the turnover pattern A previously unrecorded, second, smaller turnover, involving European mammals only, immediately precedes the Grande Coupure in the Hampshire Basin, coinciding with vegetational change This turnover is judged not to represent cooling It is concluded that the Grande Coupure coincides with the earliest Oligocene Oi-1 glaciation and that climate change combined with competition to produce the turnover
123 citations
TL;DR: A palynologically monotypic assemblage from the Eocene Jatta Gypsum Formation has been analyzed microscopically and chemically in this article, showing that the palynomorphs are solid to spongeous dinoflagellate (Division Dinophyta) remains embedded in an amorphous ground mass.
69 citations
TL;DR: Results suggest that the striking similarity in foliar physiognomy between gigantopterids and angiosperms has the potential to track Late Palaeozoic climates, although limitations of the currently available collections have prevented us from doing so in a robust manner.
43 citations
TL;DR: It is indicated that the genera GigantopterisGigantonoclea form the basis of the gigantopterid concept and current evidence suggests that Gigantpteris nicotianaefolia is restricted to the southern floral regions of Cathaysia, as typically are other species of this genus.
Abstract: Reinvestigation of the first described gigantopterid plant, Gigantopteris (Megalopteris) nicotianaefolia Schenk ex Potonie, 1902 from the Permian of China, has been conducted using the original specimens documented in 1883. The application of new techniques has permitted a comprehensive review of their morphology. This study represents the first photographic record of Schenk's specimens and provides a standardised terminology to describe them. This species of Palaeozoic leaf megaphyll is characterised by its pinnate venation, with tertiary veins that anastomose, and give rise to branches that may be of the same or higher order. These anastomosed branches form a reticulum of irregular polygonal meshes, within which higher order veins anastomose and again form meshes. On examination of Schenk's original specimens only one, MB.Pb.2002/989, can be assigned to Gigantopteris nicotianaefolia, and this is herein designated the lectotype. The remaining specimens described by Schenk are reassigned to cf. G. nicotianaefolia, cf. Gigantopteris sp., Gigantonoclea sp. or cf. Gigantonoclea sp. This re-analysis of Schenk's specimens has led to an emended diagnosis of both the genus Gigantopteris and the species G. nicotianaefolia. Current evidence suggests that Gigantopteris nicotianaefolia is restricted to the southern floral regions of Cathaysia, as typically are other species of this genus. Fertile specimens of Gigantopteris are unknown, and the status of these plants as a natural group relies upon a combination of their complex foliar physiognomy, stratigraphic range, and geographical distribution. This study indicates that the genera GigantopterisGigantonoclea form the basis of the gigantopterid concept. These two genera share characters of leaf morphology including megaphylls with eucamptodromous venation across which extends a continuous lamina, and higher order veins, third order or above, that arise from the secondary veins and anastomose to form complex meshes. These genera are distinguished in that the venation of Gigantopteris is far more complex than that of Gigantonoclea, with a greater number and complexity of vein orders, the penultimate and ultimate of which form meshes within meshes, and of these the finest may terminate in blind endings.
30 citations
TL;DR: Carbon isotope analyses were conducted on the teeth of four species of rodents and associated plant fossils from the Late Eocene-Early Oligocene Solent Group of the Hampshire Basin, UK as mentioned in this paper.
24 citations
TL;DR: In this article, a sharp morphological shift occurring within the genus Harrisichara between the Headon Hill Formation and the Bembridge Limestone Formation was found to be a functional response to changing global climate and the associated increase in seasonality.
19 citations
TL;DR: R. yushensis constitutes the first Pliocene record of Ruppia and extends the range of fossils of this genus from Europe to eastern Asia, and is the only aquatic plant in the uppermost middle part of the Zhangcun Formation.
17 citations
TL;DR: Oxygen isotope results that indicate that Thalerimys teeth with etched enamel, indicative of digestive activity, have not experienced isotopic fractionation and moulding of Thalerims teeth to produce a solid 3D record prior to sample preparation and analysis does not affect their enamel phosphate oxygen isotope values enhance the potential application of the method.
16 citations
01 Jan 2004
TL;DR: In combination, morphology, anatomy and chemistry of the resistant layers of disseminules have future potential as a powerful tool to investigate aspects of fruit and seed physiology in the past and in the present.
Abstract: Publisher Summary This chapter documents the grade of evolution of dispersal biology and ecophysiological strategies that had been attained by the Palaeogene. Plumes, which may enable “floatation” in air or may assist in orientation on landing, were lacking in Cretaceous floras and were of extremely low diversity in the Palaeogene. In contrast to plumes, wings, which may confer aerodynamic properties favoring varied dispersal trajectories and behavior, were very widespread, very abundant and highly diverse in Palaeogene floras. Small seeds, including dust and microseeds, were dominant throughout the Cretaceous. This may be as much related to parent plant stature as to a specific dispersal strategy. Like plumes, spines on disseminules are very rare in Palaeogene floras. Large dry nuts and large fleshy fruits exhibit an Eocene radiation, the former coincident with a radiation of rodents. Seed predation and survival of seeds from fleshy fruit in mammalian gut contents both indicate interactions, including potential dispersal, by mammals. Fossil fruit walls and seed coats provide a wealth of information pertinent to the further understanding of the evolution of dormancy. In combination, morphology, anatomy and chemistry of the resistant layers of disseminules have future potential as a powerful tool to investigate aspects of fruit and seed physiology in the past and in the present.
11 citations
TL;DR: The suggestion that globally extensive wildfires were ignited as part of the Cretaceous-Tertiary boundary events (e.g., this paper ) ignores the following: (1) absence of above background levels of charcoal, and absence of absence of
Abstract: The suggestion that globally extensive wildfires were ignited as part of the Cretaceous-Tertiary (K-T) boundary events (e.g., [Robertson et al., 2004][1]; [Melosh et al., 1990][2]; [Kring and Durda, 2002][3]) ignores the following: (1) absence of above background levels of charcoal, (2) absence of