No Apparent Spike of Carbon dioxide Across Cretaceous-Paleogene Boundary

Global trends of pCO2 across the Cretaceous–Paleogene boundary supported by the first Southern Hemisphere stomatal proxy-based pCO2 reconstruction

Authors:

Steinthorsdottir et al

Abstract:

Reliable reconstructions of atmospheric carbon dioxide concentrations (pCO2) are required at higher resolution than currently available to help resolve the relationship between mass extinctions and changes in palaeo-pCO2 levels. Such reconstructions are needed: 1, at a high temporal resolution for constraining the pre- and post-extinction atmospheres; and 2, at a sufficient spatial resolution to constrain potential inter-hemispheric differences. Here we estimate pCO2 based on fossil Lauraceae leaf cuticle specimens derived from three localities with strata spanning the latest Cretaceous to the mid-Paleocene, including a new Cretaceous–Paleogene boundary (K–Pg) locality, in New Zealand. We use two independent methods of stomatal density-based pCO2 reconstructions; a transfer function calibrated using herbarium material and the stomatal ratio method, producing three calibration sets. Our results based on the mean values of each of the three calibration methods indicate pCO2 ranging between ca. 460 and 650 ppm during the latest Cretaceous, falling precipitously to average values between ca. 360 and 430 ppm across the K–Pg boundary, and further to ca. 305–320 ppm in the mid-Paleocene. A ‘spike’ of extremely high pCO2 at the K–Pg could not be confirmed, but our results are, nonetheless, consistent with previously published pCO2 records from the Northern Hemisphere, and show that stomatal density worldwide was responding to significant changes in pCO2 across the K–Pg.

Evidence of the First Colonization of the Land by Plants

Mineral weathering and soil development in the earliest land plant ecosystems

Authors:

Mitchell et al

Abstract:

Land colonization by plants and their fungal and bacterial symbionts during the Paleozoic was fundamental to the evolution of terrestrial ecosystems, but how these early communities influenced mineral weathering and soil development remains largely unknown. We investigated cryptogamic ground covers (CGCs) in Iceland to identify modern analogous communities and to characterize soil structure and biologically mediated weathering features. Using a novel application of X-ray microcomputed tomography, we show that moss-dominated CGCs and their soils are not adequate analogues of early communities. Comparisons with the 407 Ma Rhynie Chert (Scotland) biota indicate that modern CGCs dominated by lichens, liverworts, and their associated symbionts (fungi, cyanobacteria) are more representative of early soil-forming communities. Liverwort and lichen soils are thin, and their depth and complexity are constrained by the size and growth form of the dominant plants or lichens. They are aggregated and stabilized by cyanobacteria, mycorrhizal and lichenized fungi, rhizoids, and associated exudates. Smectite was associated with liverwort but not with moss CGC soils. Soil grain dissolution features are diverse and attributable to different organisms (e.g., bacteria, fungi) and types of interaction (e.g., symbiosis). We postulate that such features provide a novel indirect means of inferring biotic interactions in paleosols.

Earliest land plants created modern levels of atmospheric oxygen

Earliest land plants created modern levels of atmospheric oxygen

Authors:

Lenton et al

Abstract:

The progressive oxygenation of the Earth’s atmosphere was pivotal to the evolution of life, but the puzzle of when and how atmospheric oxygen (O2) first approached modern levels (∼21%) remains unresolved. Redox proxy data indicate the deep oceans were oxygenated during 435–392 Ma, and the appearance of fossil charcoal indicates O2 >15–17% by 420–400 Ma. However, existing models have failed to predict oxygenation at this time. Here we show that the earliest plants, which colonized the land surface from ∼470 Ma onward, were responsible for this mid-Paleozoic oxygenation event, through greatly increasing global organic carbon burial—the net long-term source of O2. We use a trait-based ecophysiological model to predict that cryptogamic vegetation cover could have achieved ∼30% of today’s global terrestrial net primary productivity by ∼445 Ma. Data from modern bryophytes suggests this plentiful early plant material had a much higher molar C:P ratio (∼2,000) than marine biomass (∼100), such that a given weathering flux of phosphorus could support more organic carbon burial. Furthermore, recent experiments suggest that early plants selectively increased the flux of phosphorus (relative to alkalinity) weathered from rocks. Combining these effects in a model of long-term biogeochemical cycling, we reproduce a sustained +2‰ increase in the carbonate carbon isotope (δ13C) record by ∼445 Ma, and predict a corresponding rise in O2 to present levels by 420–400 Ma, consistent with geochemical data. This oxygen rise represents a permanent shift in regulatory regime to one where fire-mediated negative feedbacks stabilize high O2 levels.

pop sci write up.

A Major Floral Extinction 500,000 Years After the Permian-Triassic Mass Extinction (Another Pulse?)

There have been several mass extinctions in the history of Earth with adverse consequences for the environment. Researchers from the University of Zurich have now uncovered another disaster that took place around 250 million years ago and completely changed the prevalent vegetation during the Lower Triassic.

There have been several mass extinctions in the history of Earth. One of the largest known disasters occurred around 252 million years ago at the boundary between the Permian and the Triassic. Almost all sea-dwelling species and two thirds of all reptiles and amphibians died out. Although there were also brief declines in diversity in the plant world, they recovered in the space of a few thousand years, which meant that similar conditions to before prevailed again.

link.

Evidence of Wild Fires From Barremian Cretaceous Jordan

Fire in a Weichselia-dominated coastal ecosystem from the Lower Cretaceous (Barremian) of the Kurnub Group in NW Jordan

Authors:

Abu Hamad et al

Abstract:

Large intervals of the Cretaceous are considered as a ‘high-fire’ period in Earth's history. However, so far most studies dealing in greater detail with the fossil evidence of palaeo-wildfires, i.e. fossil charcoal, originate from the northern hemisphere (i.e. North America, Europe, Asia) whereas there are large stratigraphic and geographic gaps on the Cretaceous southern continents. The present paper deals with the fossil contents (plant macro-remains, palynomorphs and charcoal) of a lignite lens from the lower part of the Lower Cretaceous Kurnub Group near King Talal Dam in Jordan. The data provide evidence for the repeated occurrence of palaeo-wildfires in coastal ecosystems on the northern margin of Gondwana during the Barremian. The fossil content of the lens indicates that the vegetation, which was repeatedly affected by fire, has been dominated by the matoniaceous tree fern Weichselia reticulata. Palynological data from the lignite, as well as the repeated occurrence of wildfires point to an at least seasonally dry (or at least less humid) climate during deposition of the lignite.

Rootlets Found in Carboniferous Giant Tree Fossils

Networks of highly branched stigmarian rootlets developed on the first giant trees

Authors:

Hetherington et al

Abstract:

Lycophyte trees, up to 50 m in height, were the tallest in the Carboniferous coal swamp forests. The similarity in their shoot and root morphology led to the hypothesis that their rooting (stigmarian) systems were modified leafy shoot systems, distinct from the roots of all other plants. Each consists of a branching main axis covered on all sides by lateral structures in a phyllotactic arrangement; unbranched microphylls developed from shoot axes, and largely unbranched stigmarian rootlets developed from rhizomorphs axes. Here, we reexamined the morphology of extinct stigmarian systems preserved as compression fossils and in coal balls from the Carboniferous period. Contrary to the long-standing view of stigmarian systems, where shoot-like rhizomorph axes developed largely unbranched, root-hairless rootlets, here we report that stigmarian rootlets were highly branched, developed at a density of ∼25,600 terminal rootlets per meter of rhizomorph, and were covered in root hairs. Furthermore, we show that this architecture is conserved among their only extant relatives, herbaceous plants in the Isoetes genus. Therefore, despite the difference in stature and the time that has elapsed, we conclude that both extant and extinct rhizomorphic lycopsids have the same rootlet system architecture.

Oldest Root Stem Cells From the Carboniferous

Scientists at Oxford University have discovered the oldest known population of plant root stem cells in a 320 million-year-old fossil.

The cells, which gave rise to the roots of an ancient plant, were found in a fossilised root tip held in the Oxford University Herbaria.

As well as revealing the oldest plant root stem cells identified to date, the research also marks the first time an actively growing fossilised root has been discovered - in effect, an ancient plant frozen in time.

The study is published in the journal Current Biology.

link.

Potentially NO Aptian and Albian Cretaceous Atmospheric CO2 changes during oceanic anoxic events

Aptian and Albian atmospheric CO2 changes during oceanic anoxic events: Evidence from fossil Ginkgo cuticles in Jilin Province, Northeast China

Authors:

Sun et al

Abstract:

The Early Cretaceous was a time with super-greenhouse conditions and episodic global oceanic anoxic events. However, relative timing of atmospheric CO2 emissions and oceanic anoxic events, and their causal relationships remain matters of debate. Using the stomatal index approach, well-preserved fossil cuticles of Ginkgo from the Lower Cretaceous Changcai Formation, eastern Jilin, and from the Lower Cretaceous Yingcheng Formation, central Jilin, Northeast China, were investigated to reconstruct atmospheric CO2 concentrations during the Aptian and earliest Albian (Early Cretaceous). The results indicate that the CO2 concentrations reached 1098–1142 ppmv (Carboniferous standardization) or 970–1305 ppmv (regression function) during the Aptian and earliest Albian. Our estimates of palaeoatmospheric CO2 concentrations during the earliest Albian (OAE 1b) are slightly higher than the data between the early Aptian Selli (OAE 1a) and the middle Aptian Fallot OAEs; this may indicate the absence of any great emissions of CO2 during the latest Aptian and earliest Albian.

Estimating Carbon dioxide Levels From the Early Cretaceous

Atmospheric palaeo-CO2 estimates based on the carbon isotope and stomatal data of Cheirolepidiaceae from the Lower Cretaceous of the Jiuquan Basin, Gansu Province

Authors:

Du et al

Abstract:

The stable carbon isotope compositions and the stomatal parameters (stomatal density and stomatal index) of four Cheirolepidiaceae species, Brachyphyllum ningxiaensis, Brachyphyllum obtusum, Pseudofrenelopsis dalatzensis and Pseudofrenelopsis gansuensis, were analyzed to recover the late Early Cretaceous atmospheric CO2 levels. The fossil plants were collected from 5 consecutive sedimentary members of the uppermost Zhonggou Formation. Based on the stomatal data, the estimated palaeo-atmospheric CO2 concentrations in the Jiuquan Basin during the late Early Cretaceous were 1060–882 ppmv based on the carboniferous standardization and were 641–531 ppmv based on the recent standardization; the pCO2 values present at first a decreasing and then an increasing trend within the sedimentary time of the five members. The δ13Cp values based on the 21 Brachyphyllum specimens showed a large variation, which ranged from −20.98‰ to −25.69‰, with an average of −24.2‰. The values also identified a C3 photosynthetic pathway for the Brachyphyllum specimens. The predicted δ13Ca values varied from −2.1‰ to −6.38‰, with an average of −5.03‰. These two proxies were irregular within the different members; therefore, the correlation with the change in atmospheric CO2 concentrations was not significant. Moreover, a water-stressed environment was proposed based on the δ13C values of the present fossil plants, a proposal that was also supported by the previous palaeobotanical, palynological and stratigraphical evidence. In the present study, an inconsistent relationship between the stable carbon isotope and the stomata values was apparent, which most likely indicated that the stomata numbers of the plant were more sensitive to the variation in the concentration of the atmospheric CO2, whereas the δ13C values were sensitive to the moisture conditions.

The Paleobotanical Changes Across the Jurassic/Cretaceous Boundary in India

Integrated palaeobotanical and palynological analysis of subsurface Gondwana sedimentary succession (Jurassic–Cretaceous) in Jangareddygudem area, Chintalapudi Sub-basin, South India: Stratigraphical and phytogeographical implications

Authors:

Jha et al

Abstract:

Here we present an integrated palaeobotanical and palynological analysis of sub-surface terrestrial deposits of Jangareddygudem area, Chintalapudi Sub-basin, Godavari Graben, India. Plant megafossil impressions and palynomorphs were recovered in the bore core MJR-11 from Jangareddygudem area. Plant megafossils impressions: Equisetites sp., Ptilophyllum acutifolium, Pachypteris indica, Elatocladus jabalpurensis, Pagiophyllum gollapallensis, and Ptilophyllum cutchense are recorded at different depths in the bore core MJR-11. Palynological investigations carried out in these megafossil bearing beds reveal the presence of Coptospora sp., Ceratosporites equalis, Appendicisporites erdtmanii, Biretisporites spectabilis, Cicatricosisporites hughesii, Cicatricosisporites sp., Concavissimisporites sp., Contignisporites cooksoniae, C. fornicatus, C. glebulentus, C. multimuratus, C. psilatus, Converrucosisporites sp., Gleicheniidites sp., Klukisporites scaberis, Plicifera delicata, Balmeiopsis limbatus, Araucariacites australis, A. cooksonii, Callialasporites dampieri, C. monoalasporus, C. segmentatus, C. turbatus, Dacrycarpites australiensis, Podocarpidites ellipticus, Podosporites variabilis, Crybelosporites stylosus, and Foraminisporis wonthaggiensis. Very rare occurrence of monocolpate, tetracolpate and tricolpate pollen is also recorded. Both plant mega- and microfloral evidences indicate Late Jurrassic–Early Cretaceous (Tithonian–Valanginian) age for these sediments. A comparative study of present mega and microfossil assemblages with known megafloral and microfloral assemblage from the Upper Gondwana sediments of Godavari and other Indian basins has also been attempted. The floral assemblage clearly indicates the presence of Gangapur sediments in Jangareddygudem area.

Similarity of the Antarctic palynofloras with those known from Godavari and other basins on the east coast of India confirms continental reconstructions that show Lambert Graben of East Antarctica to have been contiguous with eastern India prior to Gondwana break-up. The non-marine character of the palynomorphs suggests that marine conditions in this region of the Godavari Graben did not develop until at least early Early Cretaceous time.

Just What Were the Noeggerathiales Plants?

Paleoecology of Noeggerathiales, an enigmatic, extinct plant group of Carboniferous and Permian times

Authors:

Pfefferkorn et al

Abstract:

Noeggerathiales are late Paleozoic plants of uncertain systematic position. They may either be late survivors of the Devonian progymnosperms or represent a sister group to ferns and sphenopsids. Noeggerathiales carry cycad-like or fern-like leaves on small, unbranched stems. They produce microspores and megaspores in cone-like structures in which sporangia are attached adaxially to sporophylls. Noeggerathiales are rare in Carboniferous and Permian fossil floras in the Euramerican floral realm (Europe and North America). Most floras do not even contain a single specimen. In the Cathaysian floral realm (China) they are more common and some fossil floras contain Noeggerathiales in substantial or even large numbers. The paleoenvironmental and taphonomic interpretations of these occurrences allow us to deduce the paleoecological preferences of Noeggerathiales. Noeggerathiales were tropical plants as can be derived from the pattern of their occurrence and the fact that tuft-trees can survive only in frost free climates. The single growing point of a tuft tree would be endangered by frost and the investment in the large leaves is so high that they have to function for at least two to three years. In Euramerica Noeggerathiales are not present in wet tropical lowland floras on clastic substrates or on most peat-deposits. However, they occur at the margin of smaller basins and on peat that was fertilized by volcanic ash. In North America several occurrences of Noeggerathialean plants are known from the base of sedimentary sections, an indication that these Noeggerathiales were part of the extrabasinal or hinterland floras. They were present before sedimentation began and could therefore be preserved by the earliest sedimentation events. Hinterland or extrabasinal floras often grew in environments that experienced a wet–dry seasonality. In China Noeggerathiales occur in species-rich lowland assemblages preserved in sediments of wet lowlands indicating that these forms were adapted to wetter conditions. The pattern indicates a plant group that was adapted to tropical climate and needed nutrient rich soil, but could withstand wet–dry seasonality. By Permian times Noeggerathiales living on the North and South China microcontinents had adapted to ever-wet climates but still needed nutrient-rich environments.

The First Report of a Forest From Mid to Late Permian China

First report of a phytogeographically mixed (transitional) Middle–Late Permian fossil wood assemblage from the Hami area, northwest China, and implications for Permian phytogeographical, paleogeographical and paleoclimatic evolution in central Asia

Authors:

Wei et al

Abstract:

A diverse and well-preserved fossil wood assemblage is described, for the first time, from the Middle Permian Taerlang Formation and the Upper Permian Quanzijie Formation in the vicinity of the Tianshan Town, Hami City of northwestern China. On the basis of wood microstructure, the fossil woods are classified into three genera and five species, including one new genus: Prototianshanoxylon gen. nov. and two new species: Prototianshanoxylon erdaogouense sp. nov., Prototianshanoxylon hamiense sp. nov. The new genus is characterized by window-like cross-field pitting and mixed tracheid radial wall pitting that suggest a transitional type between araucarioid-type and protopinoid-type pittings.

Phytogeographically, the fossil wood assemblage is characterized by an admixture of elements of both temperate Angaran (represented by wood specimens with moderately to well defined growth rings in their secondary xylem) and tropical–subtropical north subregion of the Cathaysian floras (with wood specimens lacking well-defined growth rings). Such a phytogeographically mixed fossil wood assemblage is interpreted to represent a transitional and complex climate condition between a cool temperate and tropical to subtropical zones, showing both seasonal variation and unstable climate conditions. Previously, similarly mixed floras have already been found to exist widely in northern China ranging in age from Early to Late Permian, but the mechanisms thought to be responsible for their formation were varied and remain controversial. In this study, the formation of these mixed Permian floras of North China is linked to the closure of the Tianshan–Hingan seaway coupled with the collision and amalgamation of Siberia with North China and the Tarim block, in a manner much like closing a pair of scissors with the closure of the seaway proceeding gradually and progressively from west to the east.

Lopingian Permian Niger had a Wildly Seasonal Arid Climate With Water Inundations Like the African Namib Desert and Australian Lake Eyre Basin

Biological and physical evidence for extreme seasonality in central Permian Pangea

Authors:

Looy et al

Abstract:

Climate models indicate increased desertification in the continental interior of Pangea during the Permian, which would have affected the composition of the flora and fauna. We present a multi-proxy paleoenvironmental reconstruction of a terrestrial ecosystem in central Pangea of Lopingian age. The reconstruction is based on biological and physical data from the Moradi Formation, located in the Tim Mersoi Basin, northern Niger. Paleosols and sedimentological evidence indicate that the prevailing climate was semi-arid to very arid with marked intervals of high water availability. Carbon stable isotope data from organic matter and paleosols suggest that both the soil productivity and actual evapotranspiration were very low, corresponding to arid conditions. Histological analysis of pareiasaur bones shows evidence of active metabolism and reveals distinct growth marks. These interruptions of bone formation are indicative of growth rhythms, and are considered as markers for contrasting seasonality or episodic climate events. The macrofossil floras have low diversity and represent gymnosperm-dominated woodlands. Most notable are ovuliferous dwarf shoots of voltzian conifers, and a 25-m long tree trunk with irregularly positioned branch scars. The combined biological and physical evidence suggests that the Moradi Formation was deposited under a generally arid climate with recurring periods of water abundance, allowing for a well-established ground water-dependent ecosystem. With respect to its environment, this system is comparable with modern ecosystems such as the southern African Namib Desert and the Lake Eyre Basin in Australia, which are discussed as modern analogues.

 

Better Retcon Your Angiosperm (Flowering Plant) Origin Story! Herbaceous Angiosperm Found From Callovian Jurassic China

A Whole Plant Herbaceous Angiosperm from the Middle Jurassic of China

Authors:

Han et al

Abstract:

In contrast to woody habit with secondary growth, truthful herbaceous habit lacking secondary growth is restricted to angiosperms among seed plants. Although angiosperms might have occurred as early as in the Triassic and herbaceous habit theoretically may have been well adopted by pioneer angiosperms, pre-Cretaceous herbs are missing hitherto, leaving the origin of herbs and evolution of herbaceous angiosperms mysterious. Here we report Juraherba bodae gen. et sp. nov, a whole plant herbaceous angiosperm, from the Middle Jurassic (greater than 164 Ma) at Daohugou Village, Inner Mongolia, China, a fossil Lagerst?tten that is worldwide famous for various fossil finds. The angiospermous affinity of Juraherba is ensured by its enclosed ovules/seeds. The plant is small but complete, with physically connected hairy root, stem, leaves, and fructifications. The Middle Jurassic age recommends Juraherba as the earliest record of herbaceous seed plants, demanding a refresh look at the evolutionary history of angiosperms.

A Marine Incursion in Pennsylvanian Carboniferous Canada and its Impacts

A Marine Incursion In the Lower Pennsylvanian Tynemouth Creek Formation, Canada: Implications For Paleogeography, Stratigraphy and Paleoecology

Authors:

Falcon-Lang et al

Abstract:

We document the occurrence of a marine bed, and its associated biota, in the Lower Pennsylvanian (Langsettian) Tynemouth Creek Formation of New Brunswick, and discuss its implications for paleogeography, stratigraphy, and paleoecology. This is only the second marine interval found in the entire Pennsylvanian fill of the Maritimes Basin of Canada, the other being recently found in the broadly same-age Joggins Formation of Nova Scotia. Evidence for the new marine transgression comprises an echinoderm-rich limestone that infills irregularities on a vertic paleosol surface within the distal facies of a syntectonic fluvial megafan formed under a seasonally dry tropical climate. Gray, platy ostracod-rich shales and wave-rippled sandstone beds that directly overlie the marine limestone contain trace fossils characteristic of the Mermia Ichnofacies, upright woody trees, and adpressed megafloras. This association represents bay-fills fringed by freshwater coastal forests dominated by pteridosperms, cordaites, and other enigmatic plants traditionally attributed to dryland/upland habitats. The fossil site demonstrates that marine transgressions extended farther into the interior of Pangea than has previously been documented, and may allow correlation of the Tynemouth Creek and Joggins Formations with broadly coeval European successions near the level of the Gastrioceras subcrenatum and G. listeri marine bands. It also helps explain the close similarity of faunas between the Maritimes Basin and other paleotropical basins, if transgressions facilitated migration of marine taxa into the continental interior.

The Local Flora of a Riparian Ecosystem From Barremian Cretaceous Belgium

Local-scale analysis of plant community from the Early Cretaceous riparian ecosystem of Hautrage, Belgium

Authors:

Barral et al

Abstract:

Diversity properties and relative taxon abundance are explored to describe plant community local-scale spatial and temporal patterns during four ecological stages from the middle Barremian continental aquatic ecosystem of Hautrage, Mons basin, western Belgium. Taxon co-occurrence and correlations of taxon abundance are also analyzed to describe the main patterns of plant association within each stage and through time. Diversity, relative taxon abundance and taxonomic inventory greatly vary laterally and between ecological stages. Two of these stages show gradients in taxon richness and abundance reflecting probable edge effects. A reconstruction of the plant community evolution based on these four stages plus seven previously reported stages reveal a plant community mainly composed of the conifers Arctopitys, Brachyphyllum, Frenelopsis, and Pagiophyllum, and the ferns Gleichenites and Phlebopteris, maintained through time. Two main taxon association patterns are observed over space and time: 1) Arctopitys and Phlebopteris, and 2) Brachyphyllum, Gleichenites, Pagiophyllum. Conifer type 1, Elatides and Sphenopteris appear to have been spatially associated, whereas inverse relations between Cladophlebis and Phlebopteris and between Onychiopsis and Sphenopteris reflect possible niche overlap and competitive exclusion pressures. Three different successional stages are identified by the proportion of herbaceous and woody taxa and the presence/absence of Frenelopsis. Frenelopsis was a dominant taxon in mature community stages probably forming closed canopies, and having a negative effect on richness and abundance of other taxa. Our results evidence four intense and two less intense fire events through the series, suggesting that wildfires played an important role in the ecological succession of the plant community of Hautrage. Weichselia reticulata most probably played a key role in early successional stages, contributing in the regeneration of plant communities after wildfire disturbance events.

The Vegetation of the Malawi Rift Concurrent With Plio-Pleistocene Hominin Evolution

Persistent C3 vegetation accompanied Plio-Pleistocene hominin evolution in the Malawi Rift (Chiwondo Beds, Malawi)

Authors:

Lüdecke et al

Abstract:

The development of East African savannas is crucial for the origin and evolution of early hominins. These ecosystems, however, vary widely in their fraction of woody cover and today range from closed woodland to open grassland savanna. Here, we present the first Plio-Pleistocene long-term carbon isotope (δ13C) record from pedogenic carbonate and Suidae teeth in the southern East African Rift (EAR). These δ13C data from the Chiwondo and Chitimwe Beds (Karonga Basin, Northern Malawi) represent a southern hemisphere record in the EAR, a key region for reconstructing vegetation patterns in today's Zambezian Savanna, and permit correlation with data on the evolution and migration of early hominins in today's Somali-Masai Endemic Zone. The sediments along the northwestern shore of Lake Malawi contain fossils attributed to Homo rudolfensis and Paranthropus boisei. The associated hominin localities (Uraha, Malema) are situated between the well-known hominin bearing sites of the Somali-Masai Endemic Zone in the Eastern Rift and the Highveld Grassland in southern Africa, and fill an important geographical gap for hominin research. Persistent δ13C values around −9‰ from pedogenic carbonate and suid enamel covering the last ∼4.3 Ma indicate a C3-dominated closed environment with regional patches of C4-grasslands in the Karonga Basin. The overall fraction of woody cover of 60–70% reflects significantly higher canopy density in the Malawi Rift than the Eastern Rift through time. The discrepancy between the two savanna types originated in the Late Pliocene, when the Somali-Masai ecosystem started to show increasing evidence for open, C4-dominated landscapes. Based on the Malawi δ13C data, the evolution of savanna ecosystems in Eastern Africa followed different patterns along the north-south extent of the EAR. The appearance of C4-grasses is considered a driver of evolutionary faunal shifts, but despite the difference of ecosystem evolution in the north, similar hominins and suids occurred in both landscapes, pointing to distinct habitat flexibility and also nutritional versatility.

Turonian/Coniacian Cretaceous Kholokhovchan Flora Shows Angiosperms Penetrating Into Older Ecosystems

Late Cretaceous Kholokhovchan Flora of Northeastern Asia: Composition, age and fossil plant descriptions

Authors:

Herman et al

Abstract:

The Kholokhovchan Flora comes from tuffaceous – terrigenous deposits of the Vetvinskaya Member (Chalbugchan Group) in the Penzhina and Oklan rivers interfluve, Northeastern Russia. The depositional environment of the plant-bearing deposits is interpreted to have been a freshwater lake. The Kholokhovchan Flora hosts 42 fossil plant species belonging to Marchantiopsida, Polypodiopsida, Ginkgoales, Leptostrobales, Bennettitales, Pinales and Magnoliopsida. It is characterised by diverse angiosperms, less diverse conifers and ferns, by the presence of relatively ancient Sphenobaiera, Phoenicopsis and Pterophyllum together with advanced Late Cretaceous Taxodium, Glyptostrobus and angiosperms, among which platanoids are quite diverse. The Kholokhovchan Flora is most similar to Penzhina and Kaivayam floras of the Anadyr-Koryak Subregion and Arman Flora of the Okhotsk-Chukotka volcanogenic belt (Northeastern Russia) and should be dated as Turonian–Coniacian. The Kholokhovchan Flora, that populated volcanic plateaus and intermontane valleys, are characterised by a mixture of ancient “Mesophytic” plants with typical Late Cretaceous “Cenophytic” taxa. This peculiar composition probably reflects a gradual penetration of new angiosperm-dominated plant assemblages into older floras: during the Late Cretaceous, “Cenophytic” assemblages migrated along river valleys and other disturbed habitats into the interior of Asia, eventually occupying volcanogenic uplands, and in places replacing the “Mesophytic” fern-gymnospermous communities that existed there. Two new angiosperm species, as well as four the most characteristic conifers of the Kholokhovchan Flora, are described: Cupressaceae gen. et sp. indet. cf. Widdringtonites sp., Taxodium cf. olrikii, Taxodium sp., Glyptostrobus sp., Ettingshausenia vetviensis sp. nov. and Parvileguminophyllum penzhinense sp. nov.

Xenoxylon junggarensis: a new Gymnosperm From Norian Triassic China Growth Limited by Light?

Xenoxylon junggarensis sp. nov., a new gymnospermous fossil wood from the Norian (Triassic) Huangshanjie Formation in northwestern China, and its palaeoclimatic implications

Authors:

Wan et al

Abstract:

A permineralized gymnospermous wood, Xenoxylon junggarensis sp. nov., is described from the Norian (upper Triassic) Huangshanjie Formation in Dalongkou Section, Jimsar County, Xinjiang Uygur Autonomous Region, northwestern China. The pycnoxylic wood consists of thick-walled tracheids and thin-walled rays. It is characterized by commonly rounded to very compressed, contiguous or sometimes separated uniseriate, occasionally rounded and alternate biseriate radial pits and one or two simple, large pits in each cross-field.. The fossil wood genus Xenoxylon Gothan is known to be an indicator of cooler and/or wetter climates in the boreal hemisphere during the Mesozoic. Its occurrence in the Huangshanjie Formation from Junggar Basin, together with the palaeobotanical and palynological data, indicates that a wet and temperate climate prevailed in the northern Xinjiang during the Norian interval. The mean sensitivity of analysis of 22 growth rings is 0.36, suggesting a seasonal response to climate. Growth rings in the fossil woods are large (2.3 mm average with a maximum of 5.44 mm), representing either a longer growing season or more favorable conditions for growth, including readily available water and higher temperature. Based on a considerable amount of earlywood and a small percentage of latewood and some indirect evidence, it is hypothesized that growth of X. junggarensis in the high-latitude Junggar Basin in the late Triassic was limited by light levels.

Was Atmospheric Carbon dioxide Capped at 1000 ppm Since the Beginning of the Permian?

Was atmospheric CO2 capped at 1000 ppm over the past 300 million years?

Authors:

McElwain et al

Abstract:

Atmospheric carbon dioxide concentration has shifted dynamically over the Phanerozoic according to mass balance models and the majority of proxy estimates. A new paleo-CO2 proxy method underpinned by mechanistic understanding of plant stomatal, isotopic and photosynthetic responses to CO2 has provocatively claimed that maximum paleoatmospheric CO2 was capped at 1000 ppm for the majority of the past 300 million years. Here we evaluate the robustness of the new paleo-proxy CO2 model by testing its sensitivity to initial parameterization and to scaling factors employed to estimate paleophysiological function from anatomical and morphological traits. A series of sensitivity analyses find that the model is robust to modification in some of the constants employed, such as CO2 compensation point and mesophyll conductance, resulting in variability in paleo-CO2 estimates which are already accounted for in the error propagation of the model. We demonstrate high sensitivity in the model to key input parameters such as initial fossil plant assimilation rate, termed A0 and scaling factors used to estimate stomatal conductance from measurements of fossil stomata. Incorrect parameterization of A0 has resulted in under estimation of pCO2 by as much as 600 ppm. Despite these uncertainties, our analysis highlights that the new mechanistic paleo-CO2 proxy of Franks et al. (2014) has significant potential to derive robust and more accurate CO2 estimates from fossil plant stomata, as long as parameterization of A0 is strongly justified with species appropriate morphological and anatomical data. We highlight methods that can be used to improve current estimates of fossil plant assimilation rates, reduce uncertainty associated with implementation of the Franks et al. (2014) model and importantly add to understanding of patterns of plant productivity over the Phanerozoic, for which there currently is no consensus.