Plant Fossil Record Research Articles

Fungi evolved right on track

Dating of fungal divergences with molecular clocks thus far has yielded highly inconsistent results. The origin of fungi was estimated at between 660 million and up to 2.15 billion y ago, and the divergence of the two major lineages of higher fungi, Ascomycota and Basidiomycota, at between 390 million y and up to 1.5 billion y ago. Assuming that these inconsistencies stem from various causes, we reassessed the systematic placement of the most important fungal fossil, Paleopyrenomycites, and recalibrated internally unconstrained, published molecular clock trees by applying uniform calibration points. As a result the origin of fungi was re-estimated at between 760 million and 1.06 billion y ago and the origin of the Ascomycota at 500–650 million y ago. These dates are much more consistent than previous estimates, even if based on the same phylogenies and molecular clock trees, and they are also much better in line with the fossil record of fungi and plants and the ecological interdependence between filamentous fungi and land plants. Our results do not provide evidence to suggest the existence of ancient protolichens as an alternative to explain the ecology of early terrestrial fungi in the absence of land plants.

Fossil Plant Relative Abundances Indicate Sudden Loss of Late Triassic Biodiversity in East Greenland

The pace of Late Triassic (LT) biodiversity loss is uncertain, yet it could help to decipher causal mechanisms of mass extinction. We investigated relative abundance distributions (RADs) of six LT plant assemblages from the Kap Stewart Group, East Greenland, to determine the pace of collapse of LT primary productivity. RADs displayed not simply decreases in the number of taxa, but decreases in the number of common taxa. Likelihood tests rejected a hypothesis of continuously declining diversity. Instead, the RAD shift occurred over the upper two-to-four fossil plant assemblages and most likely over the last three (final 13 meters), coinciding with increased atmospheric carbon dioxide concentration and global warming. Thus, although the LT event did not induce mass extinction of plant families, it accompanied major and abrupt change in their ecology and diversity.

Tertiary vegetation of Europe and its dynamics and climatic signal-new approaches in botany of the past

Using new methodologies for assessment of vegetation patterns and climatic proxies from the fossil plant record, considerable progress has been made in reconstructing paleoclimatic development at certain time intervals of the Neogene of Europe. Geobotanical mapping has employed new classification of zonal vegetation based on Integrated Plant Record (IPR) and developed a new technology to follow vegetation (and palaeoclimate) dynamics over large areas at a particular time slice. Improved paleoclimatic methodologies of the co-existence Approach (CA) and the Climate Leaf Analysis Multivariate Program based on dicot leaf physiognomy (CLAMP) produced climatic proxies that provided additional information on the Neogene climate over Europe. The stomatal density studies proved to be another useful tool for palaeoclimatology. New reconstructions of CO2 concentrations based on several Lauraceae and Ginkgo from the mid- Tertiary of Europe showed a positive correlation between higher levels of atmospheric CO2 (pCO2) and warming trends, expressed particularly in the Lower-Middle Miocene (“Miocene Climatic Optimum”).

Selection of Fossils for Calibration of Molecular Dating Models1

In the past decade, there has been a rise in interest in the plant fossil record. Fossils potentially provide information for assessing homology and evolutionary change (e.g., the popular missing link phenomenon), character evidence that affects phylogenetic conclusions and, thus, our understanding of modern relationships, evidence of past distributions that can aid in understanding biogeographic histories, and estimates of minimum ages of the clades to which they belong. Recently, many molecular biologists have used fossils in their analyses as a way of providing a calibration point for evolutionary models used to approximate ages for the nodes of phylogenetic trees. However, there has been little, if any, discussion of the criteria by which calibration fossils can be selected for these studies. When considering the use of a fossil as a calibration point, it is critical to take into account the quality of preservation, the method and details of identification (reliability of the taxonomic placement), and the accuracy of the published age. Here, we provide basic criteria for the use of fossils to calibrate molecular evolutionary models. These approaches not only provide better primary estimates for ages of clades, but also provide more reliable sources for those molecular biologists wishing to clean up their molecular clocks.

The Jurassic fossil plant record of the UK area

Plant life in the UK area during the three major epochs of the Jurassic (Early, Mid and Late) is discussed with emphasis on some of the groups that played an important role and/or were first described from British sediments. Palaeobotanists usually include the Rhaetian (late Triassic) in their discussions of the Early Jurassic because the Triassic/Jurassic extinction event is not very distinct in fossil floras. Rhaetian floras are often similar to Early Jurassic ones, and this overview starts with Rhaetian examples. Early Jurassic floras are rare as most of England and Wales was covered by a shallow sea at this time. However, Mid Jurassic floras are well known and diverse, especially those from Yorkshire and Stonesfield in Oxfordshire; smaller floras have been described from Scotland as well. Our knowledge about Late Jurassic floras comes mainly from Scotland and southern England.

Potomacanthus lobatus gen. et sp. nov., a new flower of probable Lauraceae from the Early Cretaceous (Early to Middle Albian) of eastern North America

A charcoalified fossil flower, Potomacanthus lobatus gen. et sp. nov., is described from the Early Cretaceous (Early to Middle Albian) Puddledock locality, Virginia, USA. Internal floral structure was studied using nondestructive synchrotron-radiation x-ray tomographic microscopy (SRXTM). The flower is bisexual and trimerous. The perianth consists of two whorls of tepals. The androecium has two whorls of fertile stamens. Anthers open by two distally hinged valves. The gynoecium consists of a single carpel that is plicate in the style and ascidiate in the ovary and contains a single pendant ovule. The fossil flower shares many similarities with flowers of extant Lauraceae and is unlike flowers of other families of Laurales. However, the fossil flower also differs in detail from all extant or fossil Lauraceae, particularly in configuration of the androecium. The new taxon, together with previously described but more fragmentary material from the Puddledock locality, provides the earliest fossil record of plants more closely related to Lauraceae than to any other extant family. It reveals several derived morphological characters that are potential synapomorphies among extant representatives of the family Lauraceae and contributes to the growing evidence for an early diversification of Laurales before the end of the Early Cretaceous.

JULIFORMIAN MILLIPEDES FROM THE LOWER DEVONIAN OF EURAMERICA: IMPLICATIONS FOR THE TIMING OF MILLIPEDE CLADOGENESIS IN THE PALEOZOIC

Two new xyloiuloid millipedes (Diplopoda: Chilognatha: Juliformia) are described and placed in the new family Gaspestriidae: Gaspestria genselorum n. gen and sp. from the Emsian of Quebec and New Brunswick and Sigmastria dilata n. gen. and sp. from the Pragian of the Midland Valley of Scotland. These new millipedes extend the stratigraphic range of xyloiuloid millipedes, which previously were only described from the Pennsylvanian of Europe and North America. All xyloiuloid millipede families are placed within the superfamily Xyloiuloidea which is left incertae sedis within Juliformia due to a lack of preservation of diagnostic characters that would allow placement within an extant order. The presence in the Lower Devonian of the superorder Juliformia, universally agreed among diplopod taxonomists to represent the most derived clade of Diplopoda, indicates that most of millipede cladogenesis leading to high-rank extant clades had to have occurred by this time, much earlier than previously indicated by the fossil record. A stratocladogram for Myriapoda is constructed, and in combination with data from the plant fossil record and nuclear protein-encoding genes, new hypotheses regarding timing of millipede high-rank cladogenesis in the Paleozoic are formulated. These include terrestrialization of Diplopoda no later than the Ordovician along with the origin of the lineage leading to Penicillata and Arthropleuridea, followed by a period of relative stasis until the Middle Silurian, at which point there was a rapid radiation of Diplopoda, producing most of the high-rank clades by the Lower Devonian.

New Oligocene–early Miocene microflora from the southwestern Turkana Basin: Palaeoenvironmental implications in the northern Kenya Rift

We report five Oligocene–early Miocene pollen assemblages from the Loperot-1 exploration well drilled in the semi-desert Lokichar Basin (latitude 02° 21′ 46.15″ N, longitude 35° 52′ 23.47″ E, ground elevation 615 m above MSL), near Lake Turkana in northern Kenya. They represent the second oldest plant microfossils so far recovered from East Africa and add significantly to the Paleogene–Neogene tropical African fossil plant record. The Loperot pollen indicate a mosaic environment of semi-deciduous forest and humid woodland whose floristic composition presents strong affinities with the vegetation occurring today in the Guinea-Congolia/Zambezia phytogeographical transition zone, with a rainfall more than 1000 mm/year and a well defined dry season. The weak representation of Poaceae and herbaceous taxa characteristic of grassland, dry bushland or savanna and the abundance of shade tolerant plants such as ferns all point to a vegetation composed to a variety of communities with closed forest formations predominant. The lack of typical temperate mountains elements, mainly Podocarpus and Juniperus today widespread on the East African highlands, indicates that the geography of the region was different from that of today. The plateaux or uplands adjacent to the Lokichar basin were probably still not high enough during this period of early rifting in East Africa to support the temperate coniferous forests characteristic of the Plio-Pleistocene.

Antarctic climate at the Eocene/Oligocene boundary — climate model sensitivity to high latitude vegetation type and comparisons with the palaeobotanical record

Simulated climate for the Antarctic continent using the GENESIS (Version 2.1) Global Climate Model with 34 Ma boundary conditions is shown to be highly sensitive to polar vegetation type. Six experiments were run using different levels of atmospheric CO 2, orbital configurations, ice sheet geometries and vegetation types to assess model sensitivity to Antarctica being covered with either a needle leaf evergreen forest or tundra. Simulations using 2× pre-industrial levels of CO 2 (combined mean annual temperature (MAT) − 19 °C) are about 7 °C cooler than minimum estimates from the Antarctic Cenozoic plant record (MAT − 12 to 15 °C). However, simulations using 3× CO 2 (MAT − 7 °C) are in good agreement with our empirical estimates of mean annual temperature. With ice sheets and orbits set up to represent early Oligocene interglacial conditions, the tundra climate is significantly cooler than the evergreen forest climate, with local, austral summer averages up to 6 °C cooler in non-glaciated areas and continental averages ∼2.5 °C cooler. In the model this is mainly due to higher albedo and decreases in net radiation and sensible and latent heat flux, especially during spring and summer. Feedbacks between coastal and continental cooling, marginal sea surface temperatures and sea ice also appear to be significant. A review of the late Palaeocene to earliest Miocene plant fossil record in the Antarctic Peninsula and Ross Sea regions shows that the vegetation was in transition ∼34 Ma, from a relatively diverse, mainly evergreen forest to a tundra vegetation. The modelled sensitivity of continental temperatures to a change from forest to tundra suggests vegetation-climate feedbacks during the Eocene–Oligocene transition played a significant role in the initial rapid glaciation of the continent.

Paleoecological Implications of Differential Biomass and Litter Production in Canopy Trees in Australian Nothofagus and Eucalyptus Forests

Abstract Taphonomic processes that may bias plant-fossil assemblages are important in explaining many aspects of the Cenozoic plant fossil record. Two tree genera, Eucalyptus and Nothofagus, are especially important for understanding the evolution of Australia's forests, because the former currently dominates the continent, whereas the latter is dominant in Cenozoic microfloras. Nothofagus also is prominent in temperate forests of South America and New Zealand, and in the Cenozoic history of these land-masses and Antarctica. This study measures standing biomass and leaf-litter production in contiguous cool temperate rainforest dominated by nanophyllous Nothofagus cunninghamii and wet sclerophyll forest dominated by macrophyllous Eucalyptus regnans in southeastern Australia. It tests an a priori hypothesis that the under-representation of Eucalyptus in the Australian Cenozoic record may reflect differential organ production by Eucalyptus and Nothofagus, respectively. A taphonomic bias was observed between ...

Origins of the southeastern Australian vegetation

Australia is an ancient continent with an interesting geological history that includes a recent major shift in its position, both globally and compared with neighbouring land masses. This has led to a great deal of confusion over many years about the origins of the Australian biomes. The plant fossil record is now clarifying this, and it is clear that the ancient Gondwanan rainforests that covered Australia while it was still part of that supercontinent contained many of the elements of the modern vegetation. However, major climatic sifting, along with responses to other factors, including soil nutrient levels, disturbance regimes, atmospheric CO2 levels, fire frequency and intensity, glaciations and the arrival of humans, have had profound impacts on the Australian vegetation, which today reflects the sum of all these factors and more. The origins of Australian vegetation and its present-day management cannot be properly understood without an appreciation of this vast history, and the fossil record has a vital role to play in maintaining the health of this continent's vegetation into the future.

Introduction and synthesis: plant phylogeny and the origin of major biomes

Phylogenetic trees based upon DNA sequence data, when calibrated with a dimension of time, allow inference of: (i) the pattern of accumulation of lineages through time; (ii) the time of origin of monophyletic groups; (iii) when lineages arrived in different geographical areas; (iv) the time of origin of biome-specific morphologies. This gives a powerful new view of the history of biomes that in many cases is not provided by the incomplete plant fossil record. Dated plant phylogenies for angiosperm families such as Leguminoaceae (Fabaceae), Melastomataceae sensu stricto, Annonaceae and Rhamnaceae indicate that long-distance, transoceanic dispersal has played an important role in shaping their distributions, and that this can obscure any effect of tectonic history, previously assumed to have been the major cause of their biogeographic patterns. Dispersal from other continents has also been important in the assembly of the Amazonian rainforest flora and the Australian flora. Comparison of dated biogeographic patterns of plants and animals suggests that recent long-distance dispersal might be more prevalent in plants, which has major implications for community assembly and coevolution. Dated plant phylogenies also reveal the role of past environmental changes on the evolution of lineages in species-rich biomes, and show that recent Plio-Pleistocene diversification has contributed substantially to their current species richness. Because of the critical role of fossils and morphological characters in assigning ages to nodes in phylogenetic trees, future studies must include careful morphological consideration of fossils and their extant relatives in a phylogenetic context. Ideal study systems will be based upon DNA sequence data from multiple loci and multiple fossil calibrations. This allows cross-validation both of age estimates from different loci, and from different fossil calibrations. For a more complete view of biome history, future studies should emphasize full taxon sampling in ecologically important groups, and should focus on geographical areas for which few species-level phylogenies are available, such as tropical Africa and Asia. These studies are urgent because understanding the history of biomes can both inform conservation decisions, and help predict the effects of future environmental changes at a time when biodiversity is being impacted on an unprecedented scale.

Historical phytogeography of the Greater Antilles

An understanding of the phytogeographic history of a region depends upon an adequate fossil record to reveal migrational histories and the timing and directions(s) of introductions and extinctions, and to augment or circumvent undue reliance on molecular clocks. It further depends upon an accurate phylogeny of the taxa to establish real patterns of geographic affinities (phylogeography), and a relatively detailed geologic history to assess the relative roles of dispersal and vicariance in populating the islands. For the Greater Antilles new information is slowly emerging on the plant fossil record through study of new floras such as the Eocene Saramaguacan palynoflora from Cuba, and more is potentially available from the middle Oligocene San Sebastian megafossil flora of Puerto Rico that has not been revised since the early 1900s. Phylogeographic studies and area cladograms are still meager for plants, but data from various animal groups are providing a context for the general biotic history of the Antilles. Perhaps the area of greatest advance is being made in achieving an adequate plate tectonic model for the Caribbean region. There is now some convergence toward a mobilist model that depicts a Cretaceous volcanic island arc that extended from the Mexico/Chortis block in the north to Ecuador in the south, and gradually moved through the developing portal between North and South America to collide with the Bahamas Platform in the middle Eocene. Throughout this 70-million-year history there was an immensely complex pattern of collision/separation and submergence/emergence that provided opportunity both for vicariance and dispersal in the migration, evolution, and speciation of the flora of the Greater Antilles.

Fossil leaves: Effective bioindicators of ancient CO2 levels?

[1] Past variations in the concentration of the greenhouse gas CO2 are thought to have played a major role in controlling Earth’s climate on preQuaternary and Quaternary timescales. To identify the contribution of CO2 to past climatic change requires accurate quantification of its content in the ancient atmosphere, and a number of proxies have been developed for this purpose (for a review see Royer et al. [2001a]). For the Late Quaternary, there is the unique opportunity to measure directly the composition of fossil air samples trapped in bubbles preserved in the polar ice sheets. Results from Antarctic ice cores reveal that the glacialinterglacial changes characterizing Quaternary climate were accompanied by variations in the atmospheric concentration of CO2 [Petit et al., 1999]. Although detection of phase relations between isotope-derived temperature estimates and trace gas concentration values is hampered by the difference in age of ice and air from the same ice sample, it is believed that CO2 lags glacial-interglacial temperature change and has acted as an amplifier of orbitally forced changes in temperature [Petit et al., 1999; Shackleton, 2000; Mudelsee, 2001].

Variation in Ginkgo biloba L. leaf characters across a climatic gradient in China.

Fossil leaves assigned to the genus Ginkgo are increasingly being used to reconstruct Mesozoic and Tertiary environments based on their stomatal and carbon isotopic characteristics. We sought to provide a more secure basis for understanding variations seen in the plant fossil record by determining the natural variability of these properties of sun and shade leaf morphotypes of Ginkgo biloba trees under the present atmospheric CO2 concentration and a range of contemporary climates in three Chinese locations (Lanzhou, Beijing, and Nanjing). Climate had no major effects on leaf stomatal index (proportion of leaf surface cells that are stomata) but did result in more variable stomatal densities. The effects of climate and leaf morphotype on stomatal index were rather conserved (<1%) and much less than the response of trees to recent CO2 increases. Leaf carbon isotope discrimination (delta) was highest for trees in Nanjing, which experience a warm, moist climate, whereas trees in the most arid site (Lanzhou) had the lowest delta values. Interestingly, the variation in delta shown by leaf populations of trees from China and the United Kingdom was very similar to that of fossil Ginkgo cuticles dating to the Mesozoic and Tertiary, which suggests to us that the physiology of leaf carbon uptake and regulation of water loss in Ginkgo has remained highly conserved despite the potential for evolutionary change over millions of years.

The biogeographic and tectonic history of India

AbstractAim To present an up to date account of the Mesozoic history of India and its relationship to the other Gondwana continents and to Eurasia.Location Continents surrounding the Western Indian Ocean.Methods Utilization of recent evidence of continental relationships based upon research in stratigraphy, palaeomagnetism, palaeontology, and contemporary biotas.Results The physical data revealed a sequence of events as India moved northward: (1) India–Madagascar rifted from east Africa 158–160 Ma (million years ago), (2) India–Madagascar from Antarctica c. 130 Ma, (3) India–Seychelles from Madagascar 84–96 Ma, (4) India from Seychelles 65 Ma, (5) India began collision with Eurasia 55–65 Ma and (6) final suturing took place c. 42–55 Ma. However, data from fossil and contemporary faunas indicate that, throughout the late Cretaceous, India maintained exchanges with adjacent lands. There is an absence in the fossil record of peculiar animals and plants that should have evolved, had India undergone an extended period of isolation just before its contact with Eurasia.Main conclusions The depiction of India in late Cretaceous as an isolated continent is in error. Most global palaeomaps, including the most recent one, show India, as it moves northward, following a track far out in the Indian Ocean. But the evidence now indicates that India's journey into northern latitudes cannot have taken place under such isolated circumstances. Although real breaks among the lands were indicated by the physical data, faunal links were maintained by vagile animals that were able to surmount minor marine barriers. India, during its northward journey, remained close to Africa and Madagascar even as it began to contact Eurasia.

New Zealand climate in the Neogene and implications for global atmospheric circulation

New Zealand has a good Neogene plant fossil record. During the Miocene it was without high topography and it was highly maritime, meaning that its climate, and the resulting vegetation, would be controlled dominantly by zonal climate conditions. Its vegetation record during this time suggests the climate passed from an ever-wet and cool but frostless phase in the Early Miocene in which Nothofagus subgenus Brassospora was prominent. Then it became seasonally dry, with vegetation in which palms and Eucalyptus were prominent and fires were frequent, and in the mid-Miocene, it developed a dry-climate vegetation dominated by Casuarinaceae. These changes are reflected in a sedimentological change from acidic to alkaline chemistry and the appearance of regular charcoal in the record. The vegetation then changed again to include a prominent herb component including Chenopodiaceae and Asteraceae. Sphagnum became prominent, and Nothofagus returned, but mainly as the subgenus Fuscospora (presently restricted to temperate climates). This is interpreted as a return to a generally wet, but now cold climate, in which outbreaks of cold polar air and frost were frequent. The transient drying out of a small maritime island and the accompanying vegetation/climate sequence could be explained by a higher frequency of the Sub-Tropical High Pressure (STHP) cells (the descending limbs of the Hadley cells) over New Zealand during the Miocene. This may have resulted from an increased frequency of ‘blocking’, a synoptic situation which occurs in the region today. An alternative hypothesis, that the global STHP belt lay at a significantly higher latitude in the early Neogene (perhaps 55°S) than today (about 30°S), is considered less likely because of physical constraints on STHP belt latitude. In either case, the difference between the early Neogene and present situation may have been a response to an increased polar–equatorial temperature gradient. This contrasts with current climate models for the geological past in which the latitude of the High Pressure belt impact is held invariant though geological time.

The fossil record and evolution of freshwater plants: a review

Palaeobotany applied to freshwater plants is an emerging field of palaeontology. Hydrophytic plants reveal evolutionary trends of their own, clearly distinct from those of the terrestrial and marine flora. During the Precambrian, two groups stand out in the fossil record of freshwater plants: the Cyanobacteria (stromatolites) in benthic environments and the prasinophytes (leiosphaeridian acritarchs) in transitional planktonic environments. During the Palaeozoic, green algae (Chlorococcales, Zygnematales, charophytes and some extinct groups) radiated and developed the widest range of morphostructural patterns known for these groups. Between the Permian and Early Cretaceous, charophytes dominated macrophytic associations, with the consequence that over tens of millions of years, freshwater flora bypassed the dominance of vascular plants on land. During the Early Cretaceous, global extension of the freshwater environments is associated with diversification of the flora, including new charophyte families and the appearance of aquatic angiosperms and ferns for the first time. Mesozoic planktonic assemblages retained their ancestral composition that was dominated by coenobial Chlorococcales, until the appearance of freshwater dinoflagellates in the Early Cretaceous. In the Late Cretaceous, freshwater angiosperms dominated almost all macrophytic communities worldwide. The Tertiary was characterised by the diversification of additional angiosperm and aquatic fern lineages, which resulted in the first differentiation of aquatic plant biogeoprovinces. hytoplankton also diversified during the Eocene with the development of freshwater diatoms and chrysophytes. Diatoms, which were exclusively marine during tens of millions of years, were dominant over the Chlorococcales during Neogene and in later assemblages. During the Quaternary, aquatic plant communities suffered from the effects of eutrophication, paludification and acidification, which were the result of the combined impact of glaciation and anthropogenic disturbance.

Plant evolution viewed through a functional and paleoclimatic prism

Plant evolution viewed through a functional and paleoclimatic prism

Willis, K.J., McElwain, J.C. The evolution of plants

Willis, K.J., McElwain, J.C. The evolution of plants