Tom L. Phillips

Stratigraphic and interregional changes in Pennsylvanian coal-swamp vegetation: Environmental inferences

Abstract Quantitative analysis of Pennsylvanian coal-swamp vegetation provides a means of inferring organization and structure of communities. Distribution of these communities further provides inferences about environmental factors, including paleoclimate. Our observations are based on in situ, structurally preserved peat deposits in coal-ball concretions from 32 coal seams in the eastern one-half of the United States and from several seams in western Europe and on spore assemblages from more than 150 seams. There were three times of particularly significant and nearly synchronous vegetational changes in the Midcontinent and Appalachian coal regions during the Pennsylvanian Period. Each was different in kind and magnitude. The first marked changes occurred during the early part of the Middle Pennsylvanian with the fluctuating decline in the high level of lycopod dominance. The abundance of cordaites increased. There was a rise in the occurrences of the lycopod herbs to form intercalated marshlands and an overall increase in floral diversity. Changes ensuing from this time also include shifts in dominant species of lycopod trees and a sustained rise in abundance and diversity of tree-fern spores. The next significant time of change was during the middle part of the Middle Pennsylvanian, representing both a culmination of earlier trends and expansions of cordaites in the Midcontinent where there was a maximum change in species without net loss of diversity. Tree ferns and medullosan pteridosperms attained subdominant levels of abundance and diverse lycopod species dominated except in the Atokan-Desmoinesian transition of the Midcontinent. The third and sharpest break occurred near the Middle—Late Pennsylvanian boundary when extinctionsof the dominant, coal-swamp lycopods allowed development of tree-fern dominance. The Late Pennsylvanian coal swamps apparently were colonized or recolonized mainly by species from outside coal swamps rather than by the survivor populations of the Middle Pennsylvanian swamps. Paralleling the changes in floras through the Pennsylvanian are changes in preservational aspects of the peat. These include a decline in shoot/root ratios from approximately 1 to

Changing patterns of Pennsylvanian coal-swamp vegetation and implications of climatic control on coal occurrence

Abstract Improved regional and interregional stratigraphic correlations of Pennsylvanian strata permit comparisons of vegetational changes in Euramerican coal swamps. The coal-swamp vegetation is known directly from in situ coal-ball peat deposits from more than 65 coals in the United States and Europe. Interpretations of coal-swamp floras on the basis of coal-ball peat studies are extended to broader regional and stratigraphic patterns by use of coal palynology. Objectives of the quantitative analyses of the vegetation in relation to coal are to determine the botanical constituents at the peat stage and their environmental implications for plant growth and peat accumulation. Morphological and paleoecological analyses provide a basis for deducing freshwater regimes of coal swamps. Changes in composition of Pennsylvanian coal-swamp vegetation are quire similar from one paralic coal region to another and show synchrony that is attributable to climate. Paleobotany and paleogeography of the Euramerican province indicate a moist tropical paleoclimate. Rainfall, runoff and evapotranspiration were the variable climatic controls in the distribution of coal-swamp vegetation, peat accumulation and coal resources. In relative terms of climatic wetness the Pennsylvanian Period is divisible into five intervals, which include two relatively drier intervals that developed during the Lower-Middle and Middle-Upper Pennsylvanian transitions. The climate during Early Pennsylvanian time was moderately wet and the median in moisture availability. Early Middle Pennsylvanian was drier, probably seasonally dry-wet; late Middle Pennsylvanian was the wettest in the Midcontinent; early Late Pennsylvanian was the driest; and late Late Pennsylvanian was probably the wettest in the Dunkard Basin. The five climatic intervals represent a general means of dividing coal resources within each region into groups with similar botanical constituents and environments of peat accumulation. Regional differences in basinal geology and climate were significant variables, but the synchronous control of paleoclimate was of primary importance.

Paleobotanical and paleoecological constraints on models of peat formation in the Late Carboniferous of Euramerica

Abstract The dominant plants of the Late Carboniferous lowland tropics were taxonomically and structurally distinct from those of any later time periods. Dominance was distributed among lycopsids, ferns, sphenopsids, pteridosperms and cordaites, and each of these groups had distinctive and different ecological preferences and amplitudes. Peat-forming habitats were dominated by lycopsids throughout the Westphalian, with a significant cordaitean element in the middle Westphalian; during the Stephanian tree ferns were dominant, following major extinctions near the Westphalian-Stephanian transition. Each of the major plant groups had distinctive architectures and tissue composition. Trees contributed up to 95% of the peat biomass and tree forms of lycopsids. Psaronius and Medullosa lack good modern analogues. The cordaites were the only woody plant group to contribute significantly to peat, and then only during the mid-Westphalian. Structurally wood-like lycopsid bark is the major “woody” tissue encountered in most Westphalian coals. Tree ferns and pteridosperms were largely parenchymatous in construction; the stigmarian root systems of lycopsids also were largely parenchymatous. The tissue structure of these dominant plant suggests the need for extreme caution in the inference of mire ecological conditions or vegetational structure from coal petrographic data. Peat formed under arborescent ferns or pteridosperms, or peat repeatedly exposed to decay and rerooting by stigmarian root systems of lycopsids, would have a distinctly non-woody signature and yet would have formed in a forested environment. A summary is presented of the autecology and synecology of mire plants, emphazing the structural framework provided by lycopsids during the Westphalian. Certain constraints in the links between peat biomass and miospore palynology are discussed in terms of over-representation, under-representation and non-representation. The formulation of Smiths four-phase hydroseral model is discussed and compared with more recent data available from plant paleoecology. The current debate over an ombrotrophic vs. rheotrophic origin of Late Carboniferous peats relies in large part on paleobotanical data, almost entirely palynological, in combination with petrographic analyses. Ecological studies of miospores and of coal-ball and compression macrofossils, and the linkage of miospores to source plants, permit the re-evaluation of mire successional models. Evidence for tree lycopsids, sphenopsids, pteridosperms and cordaites suggests growth mainly in rheotrophic mires. Tree ferns are likely candidates for growth in domed mires, although evidence is ambiguous and some tree ferns clearly grew under rheotrophic conditions. Densospores, produced by at least Sporangiostrobus lycopsid subtrees, have been considered diagnostic of ombrotrophic conditions; abundant evidence refutes this simplistic interpretation and suggests broad ecological amplitudes for densospore producers, including growth under rheotrophic conditions. Although plant fossils alone can not resolve most of the major debates in modern coal geology, paleobotany does contribute significantly to our understanding of ancient mires. An approach combining paleobotanical data with petrography, sedimentology and geochemistry, on a case by case basis, is most likely to produce a clear picture.

Comparative Ecology and Life-History Biology of Arborescent Lycopsids in Late Carboniferous Swamps of Euramerica

The comparative ecologies of Diaphorodendron, Lepidodendron, Lepidophloios, Paralycopodites (= Anabathra), and Sigillaria in Late Carboniferous coal swamps serve as a context for assessing life cycles and exploring possible structure-function relations. The distinctive aspects of the «lycopsid tree habit» in lepidodendrids are emphasized as part of the arborescent reproductive architecture of relatively short-lived (10-15 years) plants (...)

Reproduction of heterosporous arborescent lycopods in the Mississippian—Pennsylvanian of Euramerica

The reproductive organization and function of heterosporous arborescent lycopods in the Carboniferous are categorized based on histologically preserved specimens: free-sporing bisporangiate cones of the Lepidostrobus type (sensu stricto) which includes Bothrodendrostrobus, Sporangiostrobus and Polysporia; monosporangiate cones with intrasporangial modification, the Mazocarpon type; megasporangium—sporophyll modification of the monosporic, dispersed Achlamydocarpon type; and the integumentary type represented by Lepidocarpon. The taxonomy—morphology of each type of megasporophyll unit is summarized; their gametophytes and embryo stages are described and illustrated. Lycopod reproductive biology is related to swamp environments and their changes in the Pennsylvanian. The morphological and functional seed-like aspects of Achlamydocarpon and Lepidocarpon are considered aquatic adaptations, partially reflecting in their sporophyll design the leaf-cushion potentials of Lepidodendron and Lepidophloios.

Arborescent lycopod reproduction and paleoecology in a coal-swamp environment of late Middle Pennsylvanian age (herrin coal, Illinois, U.S.A.)

Abstract The arborescent lycopods dominated many coal-swamp plant communities of the Middle Pennsylvanian. A relatively small number of important species occurred in coal swamps, each with distinctive ecological requirements reflected in their reproductive biology. The major genera in the late Middle Pennsylvanian age Herrin Coal of the Illinois Basin were Lepidophloios, Lepidodendron sensu L. scleroticum and L. dicentricum, and Paralycopodites, which are dealt with in this study. Sigillaria, and Lepidodendron sensu L. hickii (true Lepidodendron), were minor parts of the vegetation. The species of these genera conform to three ecological strategies. Opportunists include Lepidophloios hallii, Lepidodendron dicentricum, and Lepidodendron hickii. These species had determinate, dendritic crowns and each tree apparently reproduced during a short, unrepeated interval late in determinate growth. They grew in areas that were disturbed or with high abiotic stress. Paralycopodites brevifolius was a colonizing species, rapidly occupying sites where peat formation was irregular, and perhaps locally disturbed by clastic influx. Paralycopodites had straight trunks with rows of deciduous lateral branches; cones were borne at the tips of the branches conferring individuals with continuous, high levels of reproduction. Displacement from sites occurred as edaphic conditions changed. Lepidodendron scleroticum and Sigillaria were site occupiers. Lepidodendron scleroticum trees individually produced the most massive wood and periderm of coalswamp lycopod species, and also had deciduous lateral branches and low but continuous reproductive output. Locally, L. scleroticum was very abundant, and such areas occurred irregularly. None of the lycopod trees had vegetative reproduction. Some Sigillaria may have been apomictic, although the major circumstantial evidence supporting this is from Upper Pennsylvanian specimens of Mazocarpon oedipternum.

Fossil plants and coal: patterns of change in pennsylvanian coal swamps of the illinois basin.

Coal palynology and studies of petrified peat indicate major changes in coal-swamp floras and the botanical constituents of coal throughout Pennsylvanian time. The changes are the result of broad climatic shifts and local environmental factors. The most striking is the change from a lycopod-dominated flora to one in which tree ferns were the major element. This change occurred at the Desmoinesian-Missourian (Westphalian-Stephanian) boundary and is probably multicontinental in scope.

Oribatid mites and the decomposition of plant tissues in Paleozoic coal-swamp forests

Although oribatid mites are essential to the decomposition of plant tissues in modern temperate forests by assisting conversion of primary productivity to soil organic matter, little is known of their paleoecologic history. Previously there has been scattered and anecdotal evidence documenting oribatid mite detritivory in Pennsylvanian plant tissues. This study evaluates the incidence of oribatid mite damage for seven major coal-ball deposits from the Illinois and Appalachian sedimentary basins, representing a 17 million year interval from the Euramerican tropics. Although this interval contains the best anatomically preserved plant tissues with oribatid mite borings in the fossil record, coeval oribatid mite body-fossils are absent. By contrast, the known body-fossil record of oribatid mites commences during the Middle Devonian, but does not reappear until the Early Jurassic, at which time mite taxa are modern in aspect. All major plant taxa occurring in Pennsylvanian coal swamps, including lycopsids, sphenopsids, ferns, seed ferns and cordaites, were consumed by oribatid mites. Virtually every type of plant tissue was used by mites, notably indurated tissues such as bark, fibrovascular bundles and especially wood, as well as softer seed megagametophytic and parenchymatic tissues within stems, roots and leaves. Significant evidence also exists for secondary consumption by mites of tissues in macroarthropod coprolites. Our data indicate that oribatid mites consumed dead, aerially-derived plant tissues at ground level, as well as root-penetrated tissues substantially within the peat. Oribatid mites were important arthropod decomposers in Pennsylvanian coal swamps of Euramerica. The wood boring functional-feeding-guild was expanded by insects into above-ground, live trees during the early Mesozoic. New food resources for insect borers resulted from penetration of live tissues such as cambium and phloem, and the invasion of heartwood and other hard tissues mediated by insect-fungus symbioses. Termites and holometabolous insects were prominent contributors to this second wave of wood-boring, exploiting gymnosperms and angiosperms as both detritivores and herbivores. An earlier emplacement of oribatid mites as detritivores of dead plant tissues continued to the present, but without a documented trace-fossil record.

Evidence of non-vascular land plants from the early Silurian (Llandoverian) of Virginia, U.S.A.

Abstract Evidence is presented for the earliest known occurrences of non-vascular land plants and of higher, septate fungi. Macerates of carbonaceous silstone lenses from the lower Massanutten Sandstone, early Silurian (Llandoverian) of Virginia, have yielded a diverse assemblage of microfossil elements. Parallel aligned, banded tubes with annular to spiral ribbing and rounded to papilliform ends, membranous cellular sheets, cuticles, trilete spores, small spore tetrads, and septate higher filamentous fungi were recovered from the macerates. The banded tubes are probably a significant analogue with supportive or conductive cell types, but are not considered tracheidal. The heterogeneous plant assemblage may represent a thalloid, non-vascular land plant, in part, with a tubular-filamentous (nematophytic) organization associated with a membranous cellular layer and cuticular covering. While no spores were established as nematophytic, the presence of trilete spores adds to the indirect evidence of multiple evolutionary convergence toward land-plant characters. This assemblage is interpreted as of land-plant origin, based on the inferred fluvial depositional model of the fossiliferous rocks. A glacio-eustatic sea-level drop in the late Ordovician is suggested as a stimulus to the advent of land plants in the early Silurian.

Clades, ecological amplitudes, and ecomorphs: phylogenetic effects and persistence of primitive plant communities in the Pennsylvanian-age tropical wetlands

Abstract Pennsylvanian-age wetland plant communities and landscape gradients exhibit persistent species composition and ecomorphic structure. Such patterns are attributable in large part to strong phylogenetic partitioning of ecological resource space at the level of higher taxa. Each of four major class-rank clades in tropical wetlands was centered in a physically distinct part of the lowland ecosystem. Once established in these physical settings clades tended to resist displacement until removed by physically driven extinction. Lycopsid trees were the principal dominants of the wettest habitats and had subpartitioned these environments along generic lines. Seed plants were the dominants on well to poorly drained clastic substrates, a diverse set of habitats reflected in high diversity of species and architectures. Sphenopsids were most abundant in aggradational environments subject to high levels of physical stress. Ferns initially were interstitial opportunists and colonizers of disturbed areas in a variety of environments. These ecological patterns were established in concert with the architectural radiation of the vascular plants, which occurred during the Devonian-Mississippian transition and established the major classes. Within the wetlands, the replacement of species by close relatives drawn from the same families or genera contributed significantly to persistence of communities and landscape gradients. Replacement was more likely to occur from within a clade where similar ecologies already existed, than from across major clades between which the basic ecologies were different. Possibly interacting with the phylogenetic factors were community and landscape level multispecies effects that may have placed limits on species replacement patterns. The existence of such emergent properties of multispecies assemblages is suggested by a breakdown of the system beginning with major, climatically induced extinctions at the Middle-Late Pennsylvanian transition. Following extinctions of the major Middle Pennsylvanian trees, opportunistic ferns gave rise to dominants in many parts of the wetlands, perhaps due to loss of some aspects of system self-regulation. As climatic drying continued seed plants began their largely passive rise to dominance in most kinds of habitats.