A rich macroflora has been collected from eleven localities in the Lower Member of the Campo Chico Formation in the Cafto Colorado area of the Sierra de Perija, Western Venezuela. A new geological map of the area has been produced. The sediments were deposited in a deltaic environment. Faunal evidence suggests an age between early Givetian and Late Devonian. Palynological preparations suggest an age of Givetian or latest Eifelian for the lower plant-bearing horizons. The plants themselves indicate a latest Eifelian-early Frasniana age. Some nineteen plant taxa are recorded, including five new genera and ten new species. They occur principally as compression fossils, although fragmentary permineralised material was discovered The lycophyte flora is composed of at least eight species belonging to the genera Ledercqia, Colpodexylon, Haskinsia, Archaeosigillaria and Lycopodites. Zosterophylls include Sawdonia and Serrulacaulis. Axes of Taeniocrada'-like appearance have probable S-type water conducting cells. Two species belonging to two new genera are attributed to the Trimerophytina, the definition of this subdivision being broadened. A new cladoxylopsidh as fertile ultimate appendages branched in a three-dimensional dichotomous manner, and recurved pairs of terminal sporangia. A compression fossil is possibly related to Iridopteridales. One species remains incertae sedis. The progymnosperms(including ?Rellimia) and a number of types of sterile axes remain unworked. Contributions have been made to the knowledge of existing taxa, particularly Archaeosigillaria, Haskinsia, Colpodexylon and Serrulacaulis. Eifelian/Frasnian floras world-wide are discussed. The Venezuelan flora, particularly the lycophyte element, is most similar to Givetian and early Frasnian assemblages from New York State, and less so to the German and Belgian assemblages which lack diverse lycophytes. A brief investigation of the biogeography of the Devonian has suggested a palaeogeographic model which is relatively consistent with the biogeographical data, and that the Venezuelan assemblages may not be representative of other Gondwanan floras

This thesis is a study of progymnosperms, an extinct group of mostly Devonian age plants believed to be inherently related to, and most likely the direct ancestors of, seed plants. Progymnosperms are characterised by a unique combination of characters found in `ferns' (free sporing reproduction) and seed plants (wood consisting of secondaryx ylem produced by a bifacial vascular cambium) and therefore play a crucial role in recording the transition between these two plant groups. The focus of this investigation has been to re-analyse progymnosperms, both as individual taxa and also as a distinct biological group, in order to understand better their role in the origin and evolution of seed plants, the dominant element of land vegetation today. Morphological investigations of several progymnosperms and a potential early seed plant form an essential foundation to the conceptual aspects of this work -a palaeophytogeographical study of progymnosperms and early seed plants, and a phylogenetic (cladistic) analysis of plants from the progymnosperm/seed plant transition. Phylogenetic analysis indicates that seed plants are monophyletic, but whether they evolved from within the aneurophytalean grade or the Archaeopteridales Glade could not be determined from the results presented in this thesis. Both the morphological investigation of Telangiopsis roskiliensis and phytogeographical analysis support the Rothwell hypothesis of seed plant evolution (aneurophytalean origin), while the phylogenetic analysis indicates

A taxonomic revision of the Cycadales in the English Wealden fossil flora constitutes the major part of this thesis. It is prefaced by short reviews of the geological setting and the previous work on the fossil flora. The nature of extant members of the Cycadales and their geological and evolutionary history are reviewed. Morphological studies together with light and scanning electron microscopy of epidermal features have allowed diagnosis and/or description of. sixteen leaf species, seven of them new, assigned to the form-genera Becklesia Seward, Ctenis Lindley & Hutton, Doratophyllum Harris, Nilssonia Brongniart, Paracycas Harris, Pseudoctenis Seward and one new genus is erected. Nilssonia schaumburgensis (Dunker) is reconstructed here as a liana-type woody climber. Four new species of scale leaves are put into the genus Deltolepis Harris which is new to the English Wealden. New evidence has revealed all known types of cycad cones with both lineages of cycad female cones represented by one species of Crossozamia Pomel (a megasporophyll of the Cycas-type) and one species of Zamiostrobus Endlicher (a female cone of the Zamia-type) with aborted ovules present. Male cones are represented by one species of Androstobus Schimper containing pollen. The Zamiostrobus and Androstobus species, for which 3D reconstructions are presented, now represent the best known cycad cones in any Mesozoic flora. Ten different types of isolated seeds are included in the genus Carpolithus Linnaeus. One trunk species is assigned to the genus Bucklandia Presl. Several species of extant cycads have been studied in microscopic detail for comparative purposes. Parallels are drawn between Mesozoic and extant genera and species, confirming the `Living Fossil' status long assigned to extant cycads. Laboratory methods employed and details of all fossil specimens studied are appended.

The Post Glacial vegetational history of the Upper Teesdale National Nature Reserve has been examined by peat stratigraphical and pollen analytical techniques in order to show the persistence of the characteristic rare plants throughout the Post Glacial period. Although little direct evidence of the rare species (i.e. macro-remains or pollen) was found, the investigations show that conditions of instability, minimal competition and the presence of soils or water with a high base status were prevalent in certain localities throughout the Post Glacial period and probably enabled the Teesdale 'rarities' to survive through a period during which processes inimical to their survival were predominant. The late cessation of solifluxion which aided in the expansion of hazel, followed by the immigration of pine, elm and oak under conditions of fluctuating water levels in the late Boreal period (zone VI) indicate the persistence of instability from Late Glacial times. At the time of the maximum expansion of woodland in the Atlantic period, although a fairly dense woodland of oak, elm and alder existed in the Upper Tees valley, Cronkley and Mickle Fells carried a heterogeneous vegetation ranging from birch-hazel and oak- birch scrub to woodland, similar to that which existed in the valley, with some peat deposits (both soligenous and ombrogenous). The disposition of these communities was influenced by edaphic factors therefore no altitudinal limit of tree growth can bedemarcated although the closed woodland limit was approximately 1700 ft (517 m). Anthropogenic activity has affected the area since Atlantic times and human interference was a major factor in the degradation of the scrubland and woodland, especially on Cronkley and Mickle Fells, and the development and spread of blanket peat, especially in localities adjacent to the limestone outcrops. The present day environment of the Teesdale 'rarities' is the result of continued instability since the Late Glacial period, particularly after the appearance of man in the Atlantic period.

Twenty two genera containing thirty eight species and nine problematic taxa of fossil plants are described from the Lower Shihhotse Formation of the Lower Permian of Dongshan, Taiyuan, North China. They include three new genera, seven new species and two new combinations. Five genera and six species are rediagnosed. The plants described include sphenophylls, discinites, marattialeans, pecopterids, alethopterids, emplecopterids, sphenopterids, tingias, cycads, cordaites and possible conifers. Discinites dentilongii sp. nov. (Noeggerathiales) is described having disc-like sporophylls with a decurrent base. The marattialean fern Taiyuanitheca tetralinea gen. et sp. nov. has four rows of circular synangia on its pinnules. The evolution of the Marattiales is discussed. Tingia Halle and Tingiostachya Konno are rediagnosed with new morphological interpretations. Shuangnangostachya gracilis gen. et sp. nov. has spirally arranged sporophylls, each with two sporangia. This taxon is assigned to a new family. Much additional information on cycads has been gained from these assemblages,: Four species of the earliest known cycad megasporophylls are described and their taxonomy clarified. Based on the attachment of the megasporophylls of Crossozamia minor sp. nov. to an axis, new evolutionary pathways of the female cycad reproductive organs are proposed.. The later appearance of similar megasporophylls in Europe suggests that migration was from northern China westwards by dispersal of seeds in ocean currents. The associated leaf Yuania Sze and two of its species are rediagnosed". Tianbaolinia circinalis gen. et sp. nov. is considered to be an immature stage in cycad leaf development. On the evidence of the plants studied here, the climate during the early Permian in the Taiyuan area is suggested to have been warm and the humidity to have varied with local topography. The unique plants of this area reconfirm the independent nature of the Cathaysian flora.

In addition to the production of phytol (from chlorophylls) and sterols, a limited number of diatom species are capable of synthesising unusual C25 and C30 highly branched isoprenoid (HBl) alkenes. At the outset of the current investigation, the structures of most C25 and C30 HBIs had been identified. Some environmental factors had been shown to control their production, although a detailed understanding of these remained unclear. In addition, the biological functions of the chemicals remained unknown, and the reasons for their production by some species and not by others, was not understood. Investigations on the distributions of C25 and C30 HBl alkenes biosynthesised by Rhizosolenia setigera demonstrated a dependence on the physiological status of the cells, as measured by the position of this diatom in its life cycle. Thus, while C30 HBIs were observed at every stage of the life cycle, C25 HBIs were not always present in the cells. Since the synthesis of C25 HBIs appears to be stimulated by the onset of auxosporulation (sexual reproduction), an explanation is provided as to why they have rarely been observed in previous studies. Two novel monocyclic C30 alkenes (previously reported in other strains of Rhizosolenia setigerd), and a novel monocyclic C25 alkene were also observed during life cycle experiments. The two C30 hydrocarbons structures were subsequently characterised and the potential geochemical relevance of these compounds was highlighted by comparison of their mass spectral and chromatographic properties with those of alkenes reported in sediments and suspended water column particles. An investigation of terpenoid (including HBl) biosynthesis in the diatoms Haslea ostrearia, Rhizosolenia setigera and Pleurosigma intermeclium has been performed. Evidence for species and organelle dependent biosynthetic pathways has been observed. Phytol is synlhesised by each species investigated according to the recently discovered methyl-erythritol phosphate (MEP) pathway. This pathway is also involved in the synthesis of C25 HBIs in the two species Haslea ostrearia and Pleio-osigma intermedium. In contrast, C25 and C30 HBIs, and (at least) one monocyclic C30 alkene, appear to be made predominantly via the mevalonate (MVA) route in the diatom R. setigera. Evidence for the contribution of the MVA pathway to the biosynthesis of sterols was found for the diatoms Rhizosolenia setigera, and Pleurosigma intermedium. In contrast, only contributions from the MEP pathway were found for the biosynthesis of sterols in Haslea ostrearia. Preliminary evidence for dynamic interchange between the two pathways has also been observed. Fractionation of Rhizosolenia setigera cells revealed that phytol was present in the chloroplasts, while sterols and HBIs were present in the cytoplasm.

No description available.

In this thesis I attempt to gather together a wide range of cladistic analysis of fossil and extant taxa representing a diverse array of phylogenetic groups. I use this data to quantitatively compare the effect of fossil taxa relative to extant taxa in terms of support for relationships, number of most parsimonious trees (MPTs) and leaf stability. In line with previous studies I find that the effects of fossil taxa are seldom different to extant taxa – although I highlight some interesting exceptions. I also use this data to compare the phylogenetic signal within vertebrate morphological data sets, by choosing to compare cranial data to postcranial data. Comparisons between molecular data and morphological data have been previously well explored, as have signals between different molecular loci. But comparative signal within morphological data sets is much less commonly characterized and certainly not across a wide array of clades. With this analysis I show that there are many studies in which the evidence provided by cranial data appears to be be significantly incongruent with the postcranial data – more than one would expect to see just by the effect of chance and noise alone. I devise and implement a modification to a rarely used measure of homoplasy that will hopefully encourage its wider usage. Previously it had some undesirable bias associated with the distribution of missing data in a dataset, but my modification controls for this. I also take an in-depth and extensive review of the ILD test, noting it is often misused or reported poorly, even in recent studies. Finally, in attempting to collect data and metadata on a large scale, I uncovered inefficiencies in the research publication system that obstruct re-use of data and scientific progress. I highlight the importance of replication and reproducibility – even simple re-analysis of high profile papers can turn up some very different results. Data is highly valuable and thus it must be retained and made available for further re-use to maximize the overall return on research investment.

No description available.

Aim: This thesis reconstructs vegetation dynamics at four key cave sites in the Western Mediterranean region (Taforalt Cave and Rhafas Cave in north-east Morocco, and Gorham's Cave and Vanguard Cave in Gibraltar), spanning the Last Interglacial-Glacial Period (c.130-13ka BP). Furthermore, it tests the hypothesis that climatic forcing played ~ major role in cultural transitions and possibly human extinction in the Late Pleistocene. Location: North-east Morocco and Gibraltar. Methods: Macroscopic charcoal, phytoliths, and charred seeds were analysed using qualitative and quantitative statistical methods. These were compared at intra-site, inter-site and inter-regional scales. Results: Results from north-east Morocco (spanning c.125- f3ka BP) suggest that local vegetation shifted on numerous occasions over the Last Glacial Period. MIS 5d-a and MIS4 vegetation was characterised by a decline in temperate Quercus deciduous and expansion in cool Cedrus atlantica, while MIS 3 and MIS 2 vegetation was largely dominated by Juniperus sp.lTetraclinis articulata, with phases of ecological stress characterised by the expansion of Pinus halepensis and Quercus evergreen. C3 grasses were dominant throughout the record. In contrast, results from Gibraltar (intermittently spanning c.130-25ka BP) ~ showed no significant changes in vegetation dynamics during this period, with (Q) vegetation dominated by Pinus pinea, with lesser frequencies of Pistacia sp., Juniperus sp., and Quercus sp. Main conclusions: This thesis provides the first evidence of Last InterglacialGlacial vegetation dynamics in north-east Morocco and Gibraltar. Results from Morocco seem to show a good association with proposed climatic variations during this time interval, while specific vegetation shifts were also broadly synchronous with cultural transitions. In contrast, the Gibraltar record suggests that vegetation remained quite stable throughout the Last Glacial Period. As such, this thesis supports the suggestion that Gibraltar was an environmental refuge during the Last Glacial Period.