The appearance of Baragwanathia (Lycophytina) in the Silurian

The evidence mainly involving graptolites is restated which supports an Upper Silurian (Ludlow) dating for a vascular flora containing Baragwanathia (Lycophytina) in Victoria, Australia.     

Morphologically complex plant macrofossils from the Late Silurian of Arctic Canada

In addition to vegetative remains, fertile remains from ten plants, representing seven distinct taxa whose size and complexity are much greater than most contemporaneous fossils, are reported from late Ludlow (Ludfordian) sediments of Bathurst Island in Nunavut, Canada. Evidence for the age of these beds is gathered from stratigraphic relationships and index fossils including conodonts, graptolites, and brachiopods. Zosterophylls dominate the collection, some of which constitute the earliest record of fertile structures arranged in dense clusters and longitudinal rows along axes. Representatives include a plant that resembles Bathurstia, one species of Zosterophyllum, and two specimens that bear affinity to this genus. Distichophytum is also represented, as is a new zosterophyll named Macivera gracilis. The prevalence of sporangial clustering and reduced sporangial stalks in this flora leads to a discussion of the origins and significance of these morphological features. Following a review of some of the other Silurian floras, particularly the Baragwanathia-bearing Lower Plant Assemblage of Victoria, Australia, which also shows morphological advancement over the rhyniophytoid-dominated floras common to Laurussia, it is concluded that the Bathurst Island flora presents the best evidence to date of substantial morphological diversity, complexity, and stature of vascular land plants in this period.     

Silurian (Wenlock–ludlow) Graptolites from Bolivia

Well preserved middle to upper Silurian (Wenlock–Ludlow) graptolites from Bolivia are described for the first time. Generally monospecific graptolite faunas, of species largely endemic to South America, are found in a few levels in the lower part of the Kirusillas, Rio Carrasco and Uncía formations. The oldest identified level yields specimens of Pristiograptus praedeubeli (Jaeger) and is referred to the upper Wenlock. Younger faunas belong to the Ludlow and include Saetograptus , Monograptus and Neodiversograptus specimens. These may be referred to the Gorstian (lower Ludlow). The fauna includes Saetograptus argentinus robustus ssp. nov. and Monograptus bolivianus sp. nov.     

Fragmentary non-vascular plant microfossils from the late Silurian of Wales

A wide variety of cuticles and tubular elements is described from a late Silurian (Ludlow Series) locality in Wales which has already yielded a macroflora containing Cooksonia Lang, Steganotheca Edwards and vascularized axes. These microfossils are compared with Lang's Downtonian .Nematothallus complex and Silurian assemblages of similar composition from north America. It is concluded that the majority of these microfossils derive from non-vascular plants of uncertain affinity which lived on land.     

Late Silurian plant microfossil assemblage from Guangyuan,Sichuan, China

A dispersed plant microfossil assemblage is described from Late Silurian deposits from Guangyuan, Sichuan, China. These strata are interpreted as nearshore, shallow marine deposits, and brachiopods suggest a late Ludlow–early Pridoli age. The palynomorph assemblage is dominated by terrestrial forms, including cryptospores and trilete spores, tubular structures and cuticle-like sheets, although rare marine acritarchs are also present. This microfossil assemblage is comparable to coeval assemblages from around the world (South and Southwest Wales; Libya; Canada; Southeastern Turkey; Northwest Spain; and Jiangsu, China). The sporomorphs from this assemblage indicate the existence of early land plants during the late Ludlow–early Pridoli in Guangyuan, Sichuan, China; and suggests that floras of this age were cosmopolitan and exhibited little palaeogeographical differentiation.     

Implications of an early land plant spore assemblage for the late Silurian age of the Si Ka Formation,northern Vietnam

The first plant microfossil assemblage from the Si Ka Formation of the Song Cau Group, northern Vietnam is reported. It is composed of cryptospores in dyads and tetrads, trilete spores, tubular remains consisting of an association of smooth, banded, and externally thickened tubes, and cuticle-like fragments. The biostratigraphic assemblage of sporomorphs indicates a late Silurian (late Ludfordian) to Early Devonian (early Lochkovian) age. Further comparison with coeval reports using the characteristic features of the assemblage confines their age to the late Ludlow (late Ludfordian) to early Přídolí. This report presents the oldest spore assemblage from Vietnam and contributes to a broader understanding of its paleo-landscape during the late Silurian.     

Plant assemblages from the Silurian of southern Bolivia and their palaeogeographic significance

Abundant but fragmentary plant fossils are described from two locations in shallow water marine facies of the Lipeón (previously Kirusilla) Formation of southern Bolivia. Field relationships and limited palaeontological data suggest that the rocks are of Ludlow to possibly early P'ídolí age (i.e. late Silurian). The majority of the fossils are sterile coalified compressions or impressions of parallel-sided axes, some with branching typical of Hostinella . No tracheids have been found and such remains are best described as rhyniophytoid. Fragments with irregular branching and variable axial diameters probably belong to algae with some similarities to Hungerfordia and Buthotrephis . Rarely axes terminate in clearly delimited globular or elliptical swellings that are interpreted as sporangia, although no spores have been recorded. The most completely preserved specimens have dichotomous branching ending in predominantly elliptical sporangia with distal borders and closely resemble Cooksonia ca-ledonica . Solitary isolated sporangia are vertically elliptical (cf. Tarrantia ), globose (cf. C. cambrensis, C. hemi-sphaerica ) or laterally extended (cf. C. pertoni ). Those with cup- or funnel-shaped morphologies superficially resemble the rhyniophytoid Steganotheca or dyad-containing Culullitheca . Thus while it is impossible to compare with confidence the taxonomic composition of Bolivian assemblages with coeval ones, their overall morphological grade is closer to material collected from circum-northern Atlantic localities than from assemblages in Australia and Kazakhsta/nChina. Palaeogeographically this translates into floristic similarities between Gondwanan high latitudes and equatorial Laurussia rather than with low latitude, north-eastern Gondwana or with a low latitude Kazakhstan/ Xinjiang micro-palaeocontinent     

Pteridophytic evolution: an often underappreciated phytological success story

The role and success of pteridophytes in the vascular land flora from the Silurian to Recent are examined. Success is defined as the ability of plants to occupy physical and ecological space through time, and evaluated in terms of species richness and percent cover. These factors are examined for vascular plants of successively more specialized grades of life cycles. Four grades, including homospory, heterospory, extreme heterospory, and angiospermy are recognized, with angiospermy providing for the greatest species richness and percent cover in the modern flora. In terms of percent cover, gymnosperms are also relatively successful, but in terms of species richness homosporous pteridophytes are more successful than all other non-angiospermous grades combined. The diversity of growth forms and life history patterns that have helped pteridophytes become successful throughout time is examined, and evidence for rhizomatous herbs, vines, epiphytes, trees of diverse architectures, and specialized modes of growth and vegetative propagation are reviewed. Comparison of several analyses of land plant diversity through the Phanerozoic suggests that plants with pteridophytic reproduction were dominant in most floras long after the origin of seed plants, and that pteridophytes probably have continued to increase in species richness up to the present. The loss of pteridophytic dominance in terms of percent cover at the end of the Paleozoic was associated with species turnover in which arborescent pteridophytes of several clades became extinct, but some herbaceous pteridophytes may have retained dominance in many floras into the Paleogene.     

Eocene plant diversity at Laguna del Hunco and Río Pichileufú, Patagonia, Argentina

The origins of South America's exceptional plant diversity are poorly known from the fossil record. We report on unbiased quantitative collections of fossil floras from Laguna del Hunco (LH) and Río Pichileufú (RP) in Patagonia, Argentina. These sites represent a frost-free humid biome in South American middle latitudes of the globally warm Eocene. At LH, from 4,303 identified specimens, we recognize 186 species of plant organs and 152 species of leaves. Adjusted for sample size, the LH flora is more diverse than comparable Eocene floras known from other continents. The RP flora shares several taxa with LH and appears to be as rich, although sampling is preliminary. The two floras were previously considered coeval. However, (40)Ar/(39)Ar dating of three ash-fall tuff beds in close stratigraphic association with the RP flora indicates an age of 47.46+/-0.05 Ma, 4.5 million years younger than LH, for which one tuff is reanalyzed here as 51.91+/-0.22 Ma. Thus, diverse floral associations in Patagonia evolved by the Eocene, possibly in response to global warming, and were persistent and areally extensive. This suggests extraordinary richness at low latitudes via the latitudinal diversity gradient, corroborated by published palynological data from the Eocene of Colombia.     

Life,death and fossilization on Gran Canaria – implications for Macaronesian biogeography and molecular dating

The Canaries have recently served as a test‐bed island system for evaluating newly developed parametric biogeographical methods that can incorporate information from molecular phylogenetic dating and ages of geological events. To use such information successfully, knowledge of geological history and the fossil record is essential. Studies presenting phylogenetic datings of plant groups on oceanic islands often through necessity, but perhaps inappropriately, use the geological age of the oldest island in an archipelago as a maximum‐age constraint for earliest possible introductions. Recently published papers suggest that there is little chance of informative fossil floras being found on volcanic islands, and that nothing could survive violent periods of volcanic activity. One such example is the Roque Nublo period in Gran Canaria, which is assumed to have caused the extinction of the flora of the island (c. 5.3–3.7 Ma). However, recent investigations of Gran Canaria have identified numerous volcanic and sedimentological settings where plant remains are common. We argue, based on evidence from the Miocene–Pliocene rock and fossil records, that complete sterilization of the island is implausible. Moreover, based on fossil evidence, we conclude that the typical ecosystems of the Canary Islands, such as the laurisilva, the Pinus forest and the thermophilous scrubland, were already present on Gran Canaria during the Miocene–Pliocene. The fossil record we present provides new information, which may be used as age constraints in phylogenetic datings, in addition to or instead of the less reliable ages of island emergences or catastrophic events. We also suggest island environments that are likely to yield further fossil localities. Finally, we briefly review further examples of fossil floras of Macaronesia.     

Early Holocene plant and animal remains from North-east Greenland

Aim The aim of this paper is to describe and interpret early Holocene floras and faunas. Location The floras and faunas come from various localities in North-east Greenland. Methods Sediment samples were wet sieved, and macrofossils picked out and dated by the AMS radiocarbon-dating method. Results Sediments, dated to the first centuries after the last glacial stage came to an abrupt end, contain a macroflora of bryophytes and a few herbs, and we suggest that these plant remains represent a pioneer vegetation entirely without woody plants. The named species of herbs are either confined to the northern parts of Greenland at present, or they become increasingly more important towards the north. Crowberry is the oldest woody plant recovered; it was present at 10.4 cal. ka BP , and it appears to have been common during the early Holocene in East Greenland. Main conclusions We suggest that the majority of the extant flora of vascular plants of East Greenland arrived by long distance dispersal during the Holocene. Some species may also have arrived during the late-glacial, and a few hardy species that are adapted to low summer temperatures may have survived the last glacial stage in nonglaciated areas. Some hardy animals may also have survived, but the majority of the fauna are considered Holocene immigrants. We suggest that migrating birds and storms, perhaps in combination, are under-appreciated dispersal vectors.     

The microfossil record of early land plants

Dispersed microfossils (spores and phytodebris) provide the earliest evidence for land plants. They are first reported from the Llanvirn (Mid-Ordovician). More or less identical assemblages occur from the Llanvirn (Mid-Ordovician) to the late Llandovery (Early Silurian), suggesting a period of relative stasis some 40 Myr in duration. Various lines of evidence suggest that these early dispersed microfossils derive from parent plants that were bryophyte-like if not in fact bryophytes. In the late Llandovery (late Early Silurian) there was a major change in the nature of dispersed spore assemblages as the separated products of dyads (hilate monads) and tetrads (trilete spores) became relatively abundant. The inception of trilete spores probably represents the appearance of vascular plants or their immediate progenitors. A little later in time, in the Wenlock (early Late Silurian), the earliest unequivocal land plant megafossils occur. They are represented by rhyniophytoids. It is only from the Late Silurian onwards that the microfossil/ megafossil record can be integrated and utilized in interpretation of the flora. Dispersed microfossils are preserved in vast numbers, in a variety of environments, and have a reasonable spatial and temporal fossil record. The fossil record of plant megafossils by comparison is poor and biased, with only a dozen or so known pre-Devonian assemblages. In this paper, the early land plant microfossil record, and its interpretation, are reviewed. New discoveries, novel techniques and fresh lines of inquiry are outlined and discussed.     

Enantiomorphous dimorphism in Silurian and Devonian bivalves; Maminka Barrande, 1881 (Lunulacardiidae, Silurian) - the oldest known example

The genus Maminka Barrande, 1881 (Lunulacardiidae) from the Wenlock and Ludlow (Silurian, Lower Paleozoic) of Europe is the oldest known bivalve with enantiomorphous dimorphism which is common among the Silurian and Devonian Lunulacardiidae and Antipleuridae. It represents the result of a special adaptation to the reclining mode of life combined with byssal attachment when early in ontogeny either the left or right valve became the lower valve; later, the bivalve develops as two enantiomorphous sets of shells. Distribution, ontogeny and evolution of this interesting feature in the genera Maminka Barrande, 1881, Stolidotus Hede, 1915, Mila Barrande, 1881, Dualina Barrande, 1881, Antipleura Barrande, 1881, Silurina Barrande, 1881 and Hercynella Kayser, 1878 are discussed.     

A diverse assemblage of early land plants from the Lower Devonian of the Welsh Borderland

FANNING, U., EDWARDS, D. & RICHARDSON, J. B., 1992. A diverse assemblage of early land plants from the Lower Devonian of the Welsh Borderland. Nine rhyniophytoid taxa are described from an early Gedinnian locality ( middle micromatus-newportensis spore Biozone) near Ludlow, England. They include Cooksonia pertoni, C. hemisphaerica, C. cambrensis, Tortilicaulis transwalliensis and three new taxa, Salopella marcensis sp. nov., Uskiella reticulata sp. nov. and Tarrantia salopensis gen. et sp. nov. Isolated sporangia of reniform shape, and those subtended by short lengths of axis, contain spores of Apiculiretusispora type and may belong to C. caledonica or Renalia . Morphologically distinctive forking, terminal sporangia lacking identifiable spores are not placed in a new taxon, because evidence based on in situ spores from elsewhere suggests they may belong to Salopella . Structures previously interpreted as clusters of sporangia of Yarravia- type are shown to be ± globular sporangia longitudinally split into valves. Sterile axes are dominated by smooth forms; although rare examples possess small enations. Tracheids have not been seen in axes of fertile specimens nor in sterile coalified compressions. A single pyrite permineralization contains tracheids of zosterophyll type. The assemblage demonstrates diversity among rhyniophytoids in the early Devonian and the existence of low vegetation 'alongside' the much larger zosterophyll dominated type.     

Phytogeography of the bryophyte floras of oak forests and páramo of the Cordillera de Talamanca, Costa Rica

Aim Central America is a biogeographically interesting area because of its location between the rich and very different biota of North and South America. We aim to assess phytogeographical patterns in the bryophyte floras of oak forests and páramo of the Cordillera de Talamanca, Costa Rica. Location Tropical America, in particular the montane area of Cordillera de Talamanca, Costa Rica. Methods The analysis is based on a new critical inventory of the montane bryophyte flora of Cordillera de Talamanca. All species were assigned to phytogeographical elements on the basis of their currently known distribution. Absolute and percentage similarities were employed to evaluate floristic affinities. Results A total of 401 species [191 hepatics (liverworts), one hornwort, 209 mosses] are recorded; of these, 251 species (128 hepatics, one hornwort, 122 mosses) occur in oak forests. Ninety‐three per cent of all oak forest species are tropical in distribution, the remaining 7% are temperate (4%) and cosmopolitan (3%) species. The neotropical element includes almost 74% of the species, the wide tropical element (pantropical, amphi‐atlantic, amphi‐pacific) only 19%. A significant part of the neotropical species from oak forests are species with tropical Andean‐centred ranges (27%). As compared with bryophyte species, vascular plant genera in the study region are represented by fewer neotropical, more temperate and more amphi‐pacific taxa. Bryophyte floras of different microhabitats within the oak forest and epiphytic bryophyte floras on Quercus copeyensis in primary, early secondary and late secondary oak forest show a similar phytogeographical make‐up to the total oak forest bryophyte flora. Comparison of oak forest and páramo reveals a greater affinity of the páramo bryophyte flora to temperate regions and the great importance of the páramo element in páramo. Surprisingly, oak forests have more Central American endemics than páramo. Main conclusions (1) Providing first insights into the phytogeographical patterns of the bryophyte flora of oak forests and páramo, we are able to confirm general phytogeographical trends recorded from vascular plant genera of the study area although the latter were more rich in temperate taxa. (2) Andean‐centred species are a conspicuous element in the bryophyte flora of Cordillera de Talamanca, reflecting the close historical connection between the montane bryophyte floras of Costa Rica and South America. (3) High percentages of Central American endemics in the bryophyte flora of the oak forests suggest the importance of climatic changes associated with Pleistocene glaciations for allopatric speciation.     

A late Wenlock flora from Co. Tipperary, Ireland

An assemblage of macroplants preserved as highly coalified compressions which lack anatomy is described from a Wenlock locality in County Tipperary, Ireland. Most of the fertile specimens are assigned to Cooksonia Lang. The taxonomic status of this genus is discussed. Some poorly preserved palynomorphs, including miospores, acritarchs, chitinozoans and a variety of tubes, have been isolated from associated sediments, but the age of the flora is based on graptolites. Sedimentological and palaeontological studies of the region are summarized. They provide little direct evidence for the habitats of the plants which are considered to have been terrestrial. The relevance of this flora to the current debate on the colonization of the land is evaluated and it is concluded that these plants provide the earliest record of erect fertile land plants of possible pteridophyte affinity.     

The Downton Series as the fourth Series of the Silurian System

A review of lithofacies and fossil distributions in the Downton strata of the Welsh Borderland and Wales indicates that these beds form a suitable basis for definition of a chronostratigraphical division of Series rank within the Silurian System. The basal boundary stratotype for the Downton Series is defined at the base of the Ludlow Bone Bed Member of the Downton Castle Sandstone Formation in a section at Whitcliffe Road, Ludlow. Shallow water marine sediments span the boundary, with no evidence of a measurable time break. Correlation of the base of the Downton Series from eastern North America through Baltoscandia and Poland suggests that it lies at or very close to the base of the Monograptus ultimus Biozone and thus approximates to the base of the Přiacute;dolí beds of Bohemia. This paper formed a submission to the Subcommission on Silurian Stratigraphy in May. 1981. □ Silurian, Downtown Series, standard subdivision, lithostratigraphy, biostratigraphy, chronostratigraphy, correlation.     

Wetland megabias: ecological and ecophysiological filtering dominates the fossil record of hot spring floras

Siliceous hot spring deposits form at Earth's surface above terrestrial hydrothermal systems, which create low‐sulphidation epithermal mineral deposits deeper in the crust. Eruption of hot spring waters and precipitation of opal‐A create sinter apron complexes and areas of geothermally influenced wetland. These provide habitat for higher plants that may be preserved in situ, by encrustation of their surfaces and permineralization of tissues, creating T⁰ plant assemblages. In this study, we review the fossil record of hot spring floras from subfossil examples forming in active hot spring areas, via fossil examples from the Cenozoic, Mesozoic and Palaeozoic to the oldest known hot spring flora, the Lower Devonian Rhynie chert. We demonstrate that the well‐known megabias towards wetland plant preservation extends to hot spring floras. We highlight that the record of hot spring floras is dominated by plants preserved in situ by permineralization on geothermally influenced wetlands. Angiosperms (members of the Cyperaceae and Restionaceae) dominate Cenozoic floras. Equisetum and gleicheniaceous ferns colonized Mesozoic (Jurassic) geothermal wetlands and sphenophytes and herbaceous lycophytes late Palaeozoic examples. Evidence of the partitioning of wetland hydrophytic and dryland mesophytic communities, a feature of active geothermal areas, is provided by well‐preserved and well‐exposed fossil sinter apron complexes, which record flooding of dryland environments by thermal waters and decline of local forest ecosystems. Such observations from the fossil record back‐up hypotheses based on active hot springs and vegetation that suggest removal of taphonomic filtering in hot spring environments is accompanied by an increase in ecological and ecophysiological filtering. To this end we also demonstrate that in the hot spring environment, the wetland bias extends beyond broad ecology. We show that ecosystems preserved from the Cenozoic to the Mesozoic provide clear evidence that the dominant plants preserved in situ by hot spring activity are also halophytic, tolerant of high pH and high concentrations of heavy metals. By extension, we hypothesize that this is also the case in Palaeozoic hot spring settings and extended to the early land plant flora of the Rhynie chert.     

New Silurian cooksonias from dolostones of north-eastern North America

New specimens of Cooksonia and Hostinella are described from the Bertie Group of Ontario and New York State, which is dated by faunas as latest Silurian (Přídolí). The rare plant fossils are unusual in that they are preserved in fine-grained, slightly argillaceous dolostones ('waterlime') rather than clastic rocks. At least two species of Cooksonia are present, one with ± globular sporangial morphology close to C. hemisphaerica Lang. Those with ellipsoidal/discoidal sporangia are compared with C. pertoni Lang, C .  paranensis Gerrienne et al . and C. bohemica Schweitzer, the latter represented by a single specimen from the Přídolí of the Czech Republic. However, the paucity of specimens, which prevents assessment of taphonomic influences on shape, combined with the absence of any anatomical features and the gross morphological simplicity of the fossils, precludes specific assignment. Specimens of Hostinella include one in which apices and a lateral basal structure resembling a root are preserved. It is concluded that the Laurentian assemblage of Ontario and New York State is less diverse and disparate than coeval assemblages, which are also preserved in marine rocks. Its preservation in limestones may have been facilitated by the hypersalinity inferred from various sedimentary features, which would restrict the activity of many decomposers.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 399–413.