Plant Megafossils Research Articles

The sedimentary environment of the Late Devonian East Greenland tetrapods

Abstract The Late Devonian early tetrapods in East Greenland occur in the Celsius Bjerg Group. Key occurrences are located in a detailed stratigraphic section used here to interpret the sedimentary palaeoenvironments. The palaeoenvironment for the Britta Dal Formation (which contains both Ichthyostega and Acanthostega ) is reinterpreted. The Britta Dal Formation channels have flat bases, are poorly channelized, are of low sinuosity and are part of a very major distributory system that periodically experienced extreme flooding. The tetrapod fossils were recovered from an ephemeral system that was not permanently habitable in the immediate area. Plant megafossils are poorly preserved casts and impressions dominated by lycopsids and fern-like plants. The overbank siltstones are dominated by arid soil forming processes and comprise a spectacular sequence of vertisols. The 1174 m in situ Ichthyostega locality in Paralleldal was relocated and occurs just below the midpoint of the second megacycle in the Britta Dal Formation.

Origin and Radiation of the Earliest Vascular Land Plants

Colonization of the land by plants most likely occurred in a stepwise fashion starting in the Mid-Ordovician. The earliest flora of bryophyte-like plants appears to have been cosmopolitan and dominated the planet, relatively unchanged, for some 30 million years. It is represented by fossilized dispersed cryptospores and fragmentary plant remains. In the Early Silurian, cryptospore abundance and diversity diminished abruptly as trilete spores appeared, became abundant, and underwent rapid diversification. This change coincides approximately with the appearance of vascular plant megafossils and probably represents the origin and adaptive radiation of vascular plants. We have obtained a diverse trilete spore occurrence from the Late Ordovician that suggests that vascular plants originated and diversified earlier than previously hypothesized, in Gondwana, before migrating elsewhere and secondarily diversifying.

Distinguishing angiophytes from the earliest angiosperms: A Lower Cretaceous (Valanginian‐Hauterivian) fruit‐like reproductive structure

A remarkably diverse Lower Cretaceous (Valanginian-Hauterivian) flora at Apple Bay, Vancouver Island, preserves seed plants at an important time of floristic evolutionary transition, about the same time as the earliest flowering plant megafossils. The fossils are permineralized in carbonate concretions and include tetrahedral seeds within cupule- or carpel-like structures. These enclosing structures, composed of elongate sclerenchyma cells with spiral thickenings that grade externally to a few layers of parenchyma, are vascularized by one collateral vascular bundle and lack trichomes. They apparently broke open to release the tightly enclosed seeds by valves. Seeds are similar to those of the Triassic seed fern Petriellaea, but are about 100 million years younger and differ in size, vascularization, integumentary anatomy, seed attachment, and number of seeds/cupule. These new seeds are described as Doylea tetrahedrasperma gen. et sp. nov., tentatively assigned to Corystospermales. Inverted cupules are reminiscent of an outer angiosperm integument rather than a carpel. Like fruits, cupules opened to release seeds at maturity, thereby foretelling several aspects of angiospermy. They show that nearly total ovule enclosure, a level of organization approaching angiospermy, was achieved by advanced seed ferns during the Mesozoic.

Early Miocene terrestrial climate inferred from plant megafossil assemblages of the Joban and Soma areas, Northeast Honshu, Japan

Five Early Miocene plant megafossil assemblages from two separate sequences in the Joban and Soma areas on the Pacific side of Northeast Japan, which are interpreted to have accumulated from vegetation in near-sea coastal lowland, are analyzed to discuss the temporal change of floral composition and causal change in terrestrial climate. The Mixed Northern Hardwood forest characterized by various species of deciduous woody dicotyledons and deciduous and evergreen conifers in Stage I (ca. 23.4 Ma) shifted gradually to a Mixed Broad-leaved deciduous forest (Stage II: ca. 21 Ma), a Mixed Broad-leaved Evergreen and Deciduous forest (Stage III: ca. 20 Ma) and a Notophyllous Broad-leaved Evergreen forest (Stages IV and V: ca. 16-17 Ma) with an appearance and subsequent increase in evergreen and deciduous species that favors warmer climatic conditions, and a decrease of taxa which inhabited cooler climates. These changes reflect an increase in mean annual temperature in the first half of the period and a decrease in mean annual range of temperature in the latter half, which were caused by mitigation of winter coldness. A quantitative analysis of mean annual temperature based on the leaf margin analysis also revealed a clear trend of increasing temperature. An abrupt change in temperature observed at the transition from Stages I to III, and warm climate during Stages IV to V can be correlated with the periods influenced by subtropical to tropical shallow-marine climate. A comparison between terrestrial and shallow-marine climates in the Joban and Soma areas probably indicates a synchronous response to climate change occurred during the Early Miocene.

Biostratigraphy of selected K/T boundary sections in southwestern North Dakota, USA: toward a refinement of palynological identification criteria

The Cretaceous/Tertiary (K/T) boundary corresponds to one of the very few unique events in the geological record discovered to date, representing a single traceable timeline across the world. This timeline, coincident with the geochemical and mineralogical singularities caused by the impact of a large extraterrestrial body, is also coincident with the end-Cretaceous extinction event in North America. This precise timeline gives an ideal context for comparing the trends recorded by the different groups of the terrestrial fossil record during the K/T extinction event. However, in southwestern North Dakota, numerous studies conducted on excellent exposures of the K/T boundary showed that the geochemical and mineralogical criteria associated with the impact are rarely preserved. For that reason, palynology is preferred as a simple and efficient way for identifying the K/T boundary. In this context, a previously undescribed outcrop section from southwestern North Dakota was found to preserve an extensive record of the continental K/T boundary with miospores and plant megafossils, as well as microvertebrates and large vertebrate elements. Preliminary studies on the fossil associations recovered from this site showed an inconsistency between the Paleocene age given by the vertebrate and megafloral component and the Cretaceous age given by the palynological record. This issue is investigated in this paper, with a major emphasis on the description and analysis of the palynological record associated with sedimentological and paleoenvironmental data. Results shows that palynologically, the K/T boundary is placed more accurately using relative abundance variations of selected taxa.

Life crises on land across the Permian–Triassic boundary in South China

The western Guizhou and eastern Yunnan area of southwest China commands a unique and significant position globally in the study of Permian–Triassic boundary (PTB) events as it contains well and continuously exposed PTB sections of marine, non-marine and marginal-marine origin in the same area. By using a range of high-resolution stratigraphic methods including biostratigraphy, eventostratigraphy, chronostratigraphy and chemostratigraphy, not only are the non-marine PTB sections correlated with their marine counterparts in the study area with high-resolution, the non-marine PTB sections of the study area can also be aligned with the PTB Global Stratotype Section and Point (GSSP) at Meishan in eastern China. Plant megafossils (“megaplants”) in the study area indicate a major loss in abundance and diversity across the PTB, and no coal beds and/or seams have been found in the non-marine Lower Triassic although they are very common in the non-marine Upper Permian. The megaplants, however, did not disappear consistently across the whole area, with some elements of the Late Permian Cathaysian Gigantopteris flora surviving the PTB mass extinction and locally even extending up to the Lower Triassic. Palynomorphs exhibit a similar temporal pattern characterized by a protracted stepwise decrease from fern-dominated spores in the Late Permian to pteridosperm and gymnosperm-dominated pollen in the Early Triassic, which was however punctuated by an accelerated loss in both abundance and diversity across the PTB. Contemporaneous with the PTB crisis in the study area was the peculiar prevalence and dominance of some fungi and/or algae species. The temporal patterns of megaplants and palynomorphs across the PTB in the study area are consistent with the regional trends of plant changes in South China, which also show a long-term decrease in species diversity from the Late Permian Wuchiapingian through the Changhsingian to the earliest Triassic, with about 48% and 77% losses of species occurring respectively in the end-Wuchiapingian and end-Changhsingian. Such consistent patterns, at both local and regional scales, contradict the hypothesis of a regional isochronous extinction of vegetation across the PTB, and hence call into question the notion that the end-Permian mass extinction was a one-hit disaster. Instead, the data from the study area and South China appears more consistent with a scenario that invokes climate change as the main driver for the observed land vegetation changes across the PTB in South China.

EXCEPTIONAL PRESERVATION OF PLANTS AND INVERTEBRATES BY PHOSPHATIZATION, RIVERSLEIGH, AUSTRALIA

Phosphatic concretions containing mineralized three-dimensional plant and invertebrate tissues occur in a mid-Cenozoic terrestrial freshwater carbonate deposit at the Riversleigh World Heritage area in northwestern Queensland, Australia. Mineralogical composition and microstructure of the concretions show that this fossil assemblage was preserved by rapid, early diagenetic phosphatization. Preserved material includes tissues typically considered to have a poor potential for phosphatization, such as internal plant structure and arthropod exoskeletal components. Phosphatization may have been mediated by the presence of microbial films. Study of this rich assemblage has the potential to make significant contributions to both the Australian Cenozoic terrestrial invertebrate fossil record and the Cenozoic plant megafossil record of northern Australia.

Some plant megafossils from the Sub-Himalayan Zone (middle Miocene) of Western Nepal

Some plant megafossils from the Sub-Himalayan Zone (middle Miocene) of Western Nepal

Biostratigraphic and palaeoenvironmental implications of an Early Cretaceous miospore assemblage from the Muling Formation, Jixi Basin, northeast China

In the Jixi Basin, eastern Heilongjiang Province, China, the lower part of the Lower Cretaceous succession consists of coal-bearing strata including the Muling Formation, which, in addition to plant megafossils, yields abundant spores and pollen grains and a few dinoflagellate cysts. The spore-pollen assemblage consists of more than 42 species belonging to 34 genera. Most of these are derived from pteridophytes and gymnosperms. The association of Aequitriradites echinatus, Cicatricosisporites australiensis, C. imbricatus, C. mediostriatus, C. undosus, Contignisporites glebulentus, Crybelosporites punctatus, Foraminisporis asymmetricus, Gleicheniidites laetus, Impardecispora purverulenta, Kuylisporites lunaris, Pilosisporites trichopapillosus and Triporoletes singularis suggests that the formation is unlikely to be older than late Hauterivian and younger than Aptian, with emphasis placed on the Barremian–early Aptian. The composition of the dinoflagellate cyst and plant megafossil assemblages is consistent with this determination. Based on palynofloral content, a comparison between the miospores recovered and the spores and pollen produced by extant plant taxa, the associated plant megafossils, and the sedimentary facies that characterize the Muling Formation, it is concluded that the source vegetation was dominated by ferns and that the climate was wet subtropical but seasonally dry.

Lithostratigraphy of the Neogene Goto Group and finding of plant megafossils in Wakamatsu-jima and Nakadori-jima, central part of Goto Islands, Nagasaki Prefecture

The Lower to early Middle Miocene Goto Group is well exposed in Nakadori-jima and Wakamatsu-jima, central part of the Goto Islands, and is divided lithologically into three formations ; Takasaki, Michidoi and Inoseto formations in ascending order. The Goto Gruop exceeds to 3600 m and represents a stratigraphic evolution beginning with thick pyroclastics deposits in lacustrine environment adjacent to volcanoes (Takasaki Formation), passing into fluvial-lacustrine environments (Michidoi Formation), and ending with deltaic environment (Inoseto Formation). The Takasaki and Michidoi formations are identified as continent marginal lake environment of southern portion of rifting of the Japan Sea. The Inoseto Formation is characterized by a dominance of northeast paleocurrent pattern and quartz-rich sandstone. This stratigraphy indicate that the Goto Group identified as the continental river-delta environments on the southern part of rifted Japan Sea. The floral assemblage found at Atotsugi in the Michidoi Formation, middle part of the Goto Group, suggests cooler climate than that of the Daijima-type flora of late Early to earliest Middle Miocene reported from the upper part of the Goto Group.

Paleobotanical analysis of materials from fossil gopher burrows and upper pleistocene host deposits, the Kolyma River lower reaches

The comparative analysis of palynomorphs and plant megafossils (fruits, seeds, twigs, leaves) in the Upper Pleistocene host sediments and materials filling in fossil burrows of gophers, their coprolites included, at the Duvannyi Yar, Stanchikovskii Yar and Zelenyi Mys sites of the Kolyma Lowland is carried out. Genera Salix, Lychnis, Silene, Draba, Potentilla, Larix, and families Poaceae, Polygonaceae, Cyperaceae, Compositae, and Leguminosae are determined among palynological remains and megafossils. Factors responsible for qualitative and quantitative differences in taxonomic compositions of palynological and megafossil assemblages are biological peculiarities of plants, different character of fossilization of palynomorphs and large plant remains, geographic conditions, different genesis of assemblages (allochthonous for microfossils and autochthonous for megafossils), and inadequately known morphology of certain spore and pollen taxa. The comprehensive paleobotanical analysis leads to the conclusion that the study region was occupied in the Late Pleistocene by plant communities of humid to somewhat dryer tundra with separate areas of pioneering and steppe vegetation.

Early Cretaceous terrestrial palynomorph assemblages from the Miyako and Tetori Groups, Japan, and their implication to paleophytogeographic provinces

Terrestrial palynomorph assemblages were found from the Lower Cretaceous Miyako Group in the Tanohata area, northeast Japan, and the Tetori Group in the Kuzuryu area, central Japan. There is no obvious difference between the assemblages from these two localities, although these localities have been regarded as belonging to different paleophytogeographic provinces in East Asia on the basis of the plant megafossils. This result is consistent with the suggestion by the recent reconsideration on the megafossil flora from the Tetori Group that the paleophytogeographic provincialism might have weakened during middle to late Early Cretaceous time. The terrestrial palynomorph assemblage from the Miyako Group has characters of both of Cerebropollenites and Schizaeoisporites palynofloras, which were proposed by previous studies, in the Northern Hemisphere during the Early Cretaceous time. This suggests an overlooked transitional palynofloral province between the Cerebropollenites and Schizaeoisporites palynofloral provinces in continental margin of Eurasia during that time.

Late Miocene to Early Pliocene vegetation of southern Europe (7–4 Ma) as reflected in the megafossil plant record

Assemblages of plant megafossils from the Late Miocene to Early Pliocene sites in southern Europe have been re-evaluated in order to get data for reconstructing the development of vegetation and climate during this time interval (7–4 Ma). Main areas of the survey are centred in Greece and adjacent countries, Italy, southern France and Spain. As a product of this study, maps of the studied area for the Late Miocene have been produced showing main physiognomic features of the forests expressed in the proportions of broad-leaved deciduous, broad-leaved evergreen, legume-type and sclerophyllous components, respectively.

Jurassic plant macrofossils from the Hojedk Formation, Kerman area, east-central Iran

The Hojedk Formation is well exposed at Dasht-e-Khak, Hashooni mine and Pabdana in the Kerman area in east-central Iran. Thirty-nine species of plant macrofossils, belonging to 21 genera from different orders, are identified in this study. The new species Todites fakhri sp. nov. (Order Osmundales) and Klukia crenata sp. nov. (Order Filicales) are described. Phyllotheca equisetitoides and Czekanowskia rigida are reported for the first time from this region. On the basis of the stratigraphic ranges of species such as Nilssonia feriziensis, Elatides thomasii, Coniopteris hymenophylloides, Nilssonia macrophylla and Klukia exilis, a Bajocian-Bathonian (early Middle Jurassic) age is suggested for the Hojedk Formation in this region. This flora resembles the plant megafossil assemblages of the upper part of Shemshak Formation which occurs widely through the central and eastern Alborz region in the north of Iran, suggesting a uniform paleoclimate and environment in Iran at this time.

A middle Eocene fossil plant assemblage (Powers Clay Pit) from western Tennessee

Plant megafossils are described, illustrated and discussed from Powers Clay Pit, occurring in the middle Eocene, Claiborne Group of the Mississippi Embayment in western Tennessee. Twenty six species and eight types of plants, and two species of insect larval cases are represented in this study. They include Lauraceae, Annonaceae, Smilacaceae, Platanaceae, Altingiaceae, Myrtaceae, Fabaceae, Fagaceae, Salicaceae, Moraceae, Rhamnaceae, Sapindaceae, Nyssaceae, Theaceae, Apocynaceae, Rubiaceae, Araliaceae, Oleaceae, entire margin morphotype 1-5, tooth margin morphotype 1, reproductive structure morphotype 1, Folindusia, and Terrindusia. Specimens collected from Powers Pit are compared to those from previous studies from western Tennessee, the Claibome Group in general, and assessed in terms of extant relationships. The extant relationships of plant megafossils described in this study provide clues to the paleoenvironment of western Tennessee during the middle Eocene. The paleoenvironment may have been subtropical accommodating warm tropical to cool temperate plant species.

Middle Pliocene sea surface temperature variability

Estimates of sea surface temperature (SST) based upon foraminifer, diatom, and ostracod assemblages from ocean cores reveal a warm phase of the Pliocene between about 3.3 and 3.0 Ma. Pollen records and plant megafossils, although not as well dated, show evidence for a warmer climate at about the same time. Increased greenhouse forcing and altered ocean heat transport are the leading candidates for the underlying cause of Pliocene global warmth. Despite being a period of global warmth, this interval encompasses considerable variability. Two new SST reconstructions are presented that are designed to provide a climatological error bar for warm peak phases of the Pliocene and to document the spatial distribution and magnitude of SST variability within the mid‐Pliocene warm period. These data suggest long‐term stability of low‐latitude SST and document greater variability in regions of maximum warming.

A multi-proxy study of lake-development in response to catchment changes during the Holocene at Lochnagar, north-east Scotland

This paper describes a multi-core lake sediment study using pollen, diatoms, and chironomids, together with magnetics and sediment biogeochemistry, as biotic and abiotic proxies to infer lake development in response to environmental change during the Holocene at Lochnagar in the eastern Highlands of Scotland. Diatoms are used to infer pH, chironomids to infer temperature, with pollen and plant megafossils acting as an independent proxy to validate these records and to provide insights into changes in catchment vegetation and soils. Lipid biomarkers are explored for their potential to provide additional information on lake productivity. The results indicate highly distinctive fluctuations in the loss-on-ignition (LOI) record, which are in phase with changes in some biotic (chironomid head-capsule concentration) and abiotic (coarse silt particle size fraction, and lipid and chlorine fractions) variables. Catchment-driven changes due to the development and degredation of soils, and the natural succession and human intervention on terrestrial catchment vegetation have the strongest influence on the diatom and chironomid assemblages. These catchment processes resulted in the natural acidification of the lake water. Post-industrial acidification of the lake was also influential on the lake biota. Climate-driven temperature change appears to have had only a weak influence on the biota with declines in cold stenothermic chironomid taxa in response to Early Holocene warming and declines in thermophilic chironomids in response to cooling at about 2600 cal. yr BP.

PERSICOSTROBUS VAEZ-JAVADI N. GEN.. A NEW EQUISETALEANSTROBILUS FROM THE TRIASSIC OF IRAN

Well-preserved and abundant plant megafossils were found at in the basal part of the Shemshak Formation in on Ozon Mountain, Alborz, NE Iran . Persicostrobus is a new equisetalean strobilus which is introduced from the Rhaetian (Upper Triassic) strata. Persicostrobus ghavideli is introduced described as the type species of this genus. Persicostrobus sp. is an immature cone of this genus.

A Late Devonian arborescent lycopsid Sublepidodendron songziense Chen emend. (Sublepidodendraceae Kräusel et Weyland 1949) from China, with a revision of the genus Sublepidodendron (Nathorst) Hirmer 1927

The study of a Late Devonian arborescent lycopsid, Sublepidodendron songziense Chen 1977, from the Hsiehchingssu (Xiejingsi) Formation of Hubei Province and the Wutung (Wutong) Formation of Anhui Province, PR China, provides new insight into its holistic architecture and taxonomic affinity. The study allows several interrelated organ species to be integrated into a conceptual whole-plant species, Sublepidodendron songziense Chen emend. Wang Q., Hao, Wang D.-M., Wang Y. et Thomas Denk. The plant consists of a monocaulous trunk growing from a stigmarian rhizomorph, the trunk bearing biseriate, sub-opposite to possibly alternate lateral branches that expand by means of isotomous to slightly anisotomous dichotomies, forming an excurrent canopy. Lateral branches bear terminal Lepidostrobus-like strobili. These strobili are dimorphic, implying separate mega- and microsporangiate strobili considered with the associated organ assemblage, including Triletes-type megaspores, Lepidocarpopsis-like sporophylls, and Lepidophloios-like cauline anatomy. Moreover, lateral branches are caducous, and ulodendroid scars mark the attachment sites of former branches onto the trunk. The plant diagnostically possesses spirally arranged, small, vertically elongated leaf cushions, which have false leaf scars. The presence of ligule cannot be excluded definitely. The characteristics of leaf cushions show considerable variation corresponding to different taphonomic processes, preservational modes and ontogenetic stages so that this plant megafossil has been classified in various ways previously. Based on organic connection and cauline anatomy, a reconstruction of the whole-plant species is tentatively given. We compare this whole-plant species to the type species S. mirabile (Nathorst) Hirmer, and revise Sublepidodendron (Nathorst) Hirmer 1927, suggesting that the genus and its own family Sublepidodendraceae sensu Kräusel et Weyland 1949 should be separated from the order Protolepidodendrales sensu Pichi-Sermolli 1958 and referred to the order Isoëtales sensu lato and the suborder Dichostrobiles sensu DiMichele et Bateman 1996. Present Ulodendron specimens are the earliest record in the Late Palaeozoic strata, demonstrating that the pseudomonopodial branching architectural form in the arboresent lycopsids had evolved by the Late Devonian (Famennian). Such a woody trunk together with lateral branches (or cauline peduncles), separate mega- and microsporangiate strobili, and rootlet-bearing rhizomorph epitomize the major structural units (or architectural modules) of a true arborescent lycopsid, and S. songziense appears to be the oldest arborescent lycopsid showing an apparently centralized rhizomorph. We suggest that phylogenetically more advanced arborescent lycopsids did not precipitately occur in the Carboniferous, rather they had already evolved by the Late Devonian (Famennian). The widespread genus Sublepidodendron (Nathorst) Hirmer 1927 emend., especially abundant in China, among the Late Devonian–Early Carboniferous floras may represent one of the progenitors of the phylogenetically advanced arborescent lycopsids.

Preliminary analysis of climate indicator plant distribution in the Early Cretaceous of China

We review the distribution of Early Cretaceous megafossil plants from China. The distribution patterns of Ginkgoales, Acanthopteris, Nilssonia, Podozamites, Gleichenites, frenelopsids, Otozamites, Zamites, Zamiophyllum, Ptilophyllum, and Weichselia are illustrated on maps. The Early Cretaceous flora of China has been divided into two floristic provinces. The ‘Northern type’ (Tetori-type or Siberia-Canadian) flora flourished under a warm-temperate and humid climate while the ‘Southern type’ (Ryoseki-type or Euro-Sinian) flora flourished under a tropical–subtropical and rather arid climate. Although most researchers agree with the estimations of climate mentioned above, the locations of the boundary between these two floristic provinces and their mixed zone are still controversial. Distribution maps from the present study show that each taxon has a different distribution area. This means that the boundary positions advocated previously are not supported by the present study. These results indicate that an objective methodology is needed for further study. To solve this problem, we compiled a database of the Early Cretaceous flora and its components in East Asia, which includes all the taxa described in the referenced publications.