Romer's Gap Plugged: 5 new Tetrapods From Tournaisian Mississippian Carboniferous Scotland

Phylogenetic and environmental context of a Tournaisian tetrapod fauna

Authors:

Clack et al

Abstract:

The end-Devonian to mid-Mississippian time interval has long been known for its depauperate palaeontological record, especially for tetrapods. This interval encapsulates the time of increasing terrestriality among tetrapods, but only two Tournaisian localities previously produced tetrapod fossils. Here we describe five new Tournaisian tetrapods (Perittodus apsconditus, Koilops herma, Ossirarus kierani, Diploradus austiumensis and Aytonerpeton microps) from two localities in their environmental context. A phylogenetic analysis retrieved three taxa as stem tetrapods, interspersed among Devonian and Carboniferous forms, and two as stem amphibians, suggesting a deep split among crown tetrapods. We also illustrate new tetrapod specimens from these and additional localities in the Scottish Borders region. The new taxa and specimens suggest that tetrapod diversification was well established by the Tournaisian. Sedimentary evidence indicates that the tetrapod fossils are usually associated with sandy siltstones overlying wetland palaeosols. Tetrapods were probably living on vegetated surfaces that were subsequently flooded. We show that atmospheric oxygen levels were stable across the Devonian/Carboniferous boundary, and did not inhibit the evolution of terrestriality. This wealth of tetrapods from Tournaisian localities highlights the potential for discoveries elsewhere.

pop sci write up.

Tournaisian Mississipian Tetrapods of Scotland Lived in a Seasonal Mosaic Tropical Forest

The terrestrial landscapes of tetrapod evolution in earliest Carboniferous seasonal wetlands of SE Scotland

Authors:

Kearsey et al

Abstract:

The Lower Mississippian (Tournaisian) Ballagan Formation in SE Scotland yields tetrapod fossils that provide fresh insights into the critical period when these animals first moved onto land. The key to understanding the palaeoenvironments where they lived is a detailed analysis of the sedimentary architecture of this formation, one of the thickest and most completely documented examples of a coastal floodplain and marginal marine succession from this important transitional time anywhere in the world. Palaeosols are abundant, providing a unique insight into the early Carboniferous habitats and climate.

More than 200 separate palaeosols are described from three sections through the formation. The palaeosols range in thickness from 0.02 to 1.85 m and are diverse: most are Entisols and Inceptisols (63%), indicating relatively brief periods of soil development. Gleyed Inseptisols and Vertisols are less common (37%). Vertisols are the thickest palaeosols (up to 185 cm) in the Ballagan Formation and have common vertic cracks. Roots are abundant through all the palaeosols, from shallow mats and thin hair-like traces to sporadic thicker root traces typical of arborescent lycopods.

Geochemical, isotope and clay mineralogical analyses of the palaeosols indicate a range in soil alkalinity and amount of water logging. Estimates of mean annual rainfall from palaeosol compositions are 1000–1500 mm per year. The high mean annual rainfall and variable soil alkalinities contrast markedly with dry periods that developed deep penetrating cracks and evaporite deposits. It is concluded that during the early Carboniferous, this region experienced a sharply contrasting seasonal climate and that the floodplain hosted a mosaic of closely juxtaposed but distinct habitats in which the tetrapods lived. The diversification of coastal floodplain environments identified here may link to the evolution and movement of tetrapods into the terrestrial realm.

New insights on East Finnmark Platform palynostratigraphy

New insights on East Finnmark Platform palynostratigraphy and paleogeography — A study of three shallow cores from a Mississippian succession in the Barents Sea, Norway

Authors:

Lopes et al

Abstract:

Palynomorph assemblages from cores from three shallow stratigraphic boreholes (7029/3-U-1; 7127/10-U-2; 7127/10-U-3) drilled on the East Finnmark Platform have enabled the recognition of four miospore assemblages and two sub-assemblages from the Billefjorden Group in this area, rectifying earlier biozonations. The assemblages are correlated to the Western European biozonation and are based mainly on taxa abundance and the first and last appearances of selected species. All assemblages are Visean to possibly early Serpukhovian in age. Correlations with other biozonations from areas of similar paleolatitude are suggested. Our results suggest that strata assigned to the Billefjorden Group in the offshore may be slightly older than previously assumed. Even so, the Billefjorden Group succession in the offshore is younger than that recognized in the onshore. A mixed signature between the flora from the Arctic region and areas further south in the Euramerican Supercontinent has been observed which may be indicative that the Finnmark Platform was located in a microfloristic transitional region. Generically, the climate in this region was humid and warm during the Visean time which is reflected in the significant amount of neutral, humid and moderately humid floral elements represented by the miospore assemblages.

Palaeoenvironments of the Middle–Late Mississippian Moscow Basin were a Everglades Analog

Palaeoenvironments of the Middle–Late Mississippian Moscow Basin (Russia) from multiproxy study of palaeosols and palaeokarsts

Authors:

Alekseeva et al

Abstract:

Numerous pedogenically altered subaerial exposure surfaces within Middle–Late Mississippian (Viséan–Serpukhovian) shallow carbonates in the Moscow Basin attest to sea-level fluctuations and climate change. In total, fifteen palaeosols at seven stratigraphical levels from five open pits were described and studied in detail. They show both stratigraphic and lateral soil type variability. The factors of major influence are substrate type, time of exposure (tectonics and relief), and climate. All palaeosols are polycyclic and consist of at least two parts. The lower unit (substrate), consisting mainly of limestone, with siliciclastic deltaic and palustrine beds, was altered to different degrees by weathering/pedogenesis. Depending on climate, the limestone was transformed into calcrete or caliche. The substrate is capped by a terrigeneous topclay which represents an individual palaeosol developed prior to subsequent marine flooding. Indications of gley conditions, as well as the presence of coal, sphaerosiderite and framboidal pyrite, indicate a wet peat–swamp environment that was, however, periodically dry. The calculated mean annual precipitation (MAP) based on a CIA-K proxy of siliciclastic units shows that the climate was characterized by alternating periods of aridity and humidity, with the most humid conditions (~ 1250 mm) during the middle Visean. The same proxy applied to Late Mississippian sediments of the Appalachian Basin shows a similar MAP range. High-amplitude sea-level fluctuations at the Mikhailovian–Venevian boundary followed by prolonged exposure resulted in the development of a laterally extensive deep karst capped by a pedocomplex and then by a palustrine bed. The structure and scale of this unconformity are comparable to those of the Florida Everglades environment, which represents a modern marsh landscape. The majority of topclays are smectitic, except for the most humid and most arid environments, which are dominated by kaolinite and palygorskite, respectively. Besides mineralogy, we also provide data regarding geochemistry, carbon isotopic composition of carbonate, organic matter characteristics including solid state 13C NMR and δ13C data, and evidence of vegetation types based on field observations and SEM images.

Consider Romer's Gap Plugged! New Floodplain Siltstone Deposit From Scotland Preserves Tetrapods From Tournaisian Carboniferous

Early Mississippian sandy siltstones preserve rare vertebrate fossils in seasonal flooding episodes

Authors:

Bennett et al

Abstract:

Flood-generated sandy siltstones are under-recognised deposits that preserve key vertebrate (actinopterygians, rhizodonts, and rarer lungfish, chondrichthyans and tetrapods), invertebrate and plant fossils. Recorded for the first time from the Lower Mississippian Ballagan Formation of Scotland, more than 140 beds occur throughout a 490 m thick core succession characterised by fluvial sandstones, palaeosols, siltstones, dolostone ‘cementstones’ and gypsum from a coastal–alluvial plain setting. Sandy siltstones are described as a unique taphofacies of the Ballagan Formation. They are matrix-supported siltstones with millimetre-sized siltstone and very fine sandstone lithic clasts. Common bioclasts include plants and megaspores, fish, ostracods, eurypterids and bivalves. Fossils have a high degree of articulation compared with those found in other fossil-bearing deposits such as conglomerate lags at the base of fluvial channel sandstones. Bed thickness and distribution varies throughout the formation, with no stratigraphic trend. The matrix sediment and clasts are sourced from the reworking of floodplain sediments including desiccated surfaces and palaeosols. Secondary pedogenic modification affects 30% of the sandy siltstone beds and most (71%) overlie palaeosols or desiccation cracks. Sandy siltstones are interpreted as cohesive debris flow deposits that originated by the overbank flooding of rivers and due to localised floodplain sediment transport at times of high rainfall; their association with palaeosols and desiccation cracks indicates seasonally wet to dry cycles throughout the Tournaisian. Tetrapod and fish fossils derived from floodplain lakes and land surfaces are concentrated by local erosion and reworking and are preserved by deposition into temporary lakes on the floodplain; their distribution indicates a local origin, with sediment distributed across the floodplain in seasonal rainfall episodes. These deposits are significant new sites that can be explored for the preservation of rare non-marine fossil material and provide unique insights into the evolution of early terrestrial ecosystems.

The Role of Continental Drift & Glaciations on Carbonifierous PaleoClimates

Impact of continental motion and dynamic glaciations on low-latitude climate during the Carboniferous: The record of the Wyoming Shelf (Western United States)

Authors:

Blanchard et al

Abstract:

The dynamic character of the Late Paleozoic Ice Age is evident from glacial deposits, but its impact on tropical climate is not well constrained. Global changes in climate are overprinted on longer-term paleogeographic variations, resulting in a complex time–space distribution of climate-sensitive lithologies. The significance of such lithologies in Carboniferous successions of the western United States has not been fully explored. In this study, we provide new interpretations for the paleoclimatic context of the Amsden and Tensleep Formations (Pennsylvanian, Northern Wyoming, USA). The Amsden Formation consists of a basal sandstone member overlain by red siltstones containing pisolites. Very large-scale (~ 10 m) cross-bedding within the basal sandstone indicates deposition in an erg environment. Iron pisoid-rich layers in the overlying member suggest an evolution toward more humid conditions. Persistent arid conditions during the middle Pennsylvanian are suggested by eolian sandstones and calcretes in the overlying Tensleep Formation. These formations were deposited on the karst topography that developed on top of the lower to middle Mississippian Madison Group. Although the development of karstic features implies that humid conditions prevailed during the late Mississippian, evaporites and evidence for early dolomitization within the formation suggest that it was deposited under arid conditions. These relationships argue for a long-term climate evolution from arid to humid during the Mississippian, and a return to arid conditions during the Pennsylvanian. This trend can be explained by the northward drift from ~ 15°S to ~ 12°N. A comparison with contemporaneous records reveals a diachronous evolution across western Pangaea, with the climatic conditions documented on the Wyoming Shelf being reached later in eastern North America. These relationships indicate that plate motion considerably overprints long-term climatic records. Departures from this trend, suggested by the presence of erg deposits in the basal Amsden Formation, record the overprinting of shorter periods of climate change.

Ward Takes a hit, Romer's Gap not Real: Diverse Tournaisian Mississipian Carboniferous Tetrapods From Nova Scotia Include Several Devonian Taxa

A Diverse Tetrapod Fauna at the Base of 'Romer's Gap'

Authors:

Anderson et al

Abstract:

The lack of fossil tetrapod bearing deposits in the earliest Carboniferous (‘Romer’s Gap’) has provoked some recent discussions regarding the proximal cause, with three explanations being offered: environmental, taphonomic, and collection failure. One of the few, and earliest, windows into this time is the locality of Blue Beach exposed in the Tournaisian deposits at Horton Bluff lying along the Avon River near Hantsport, Nova Scotia, Canada. This locality has long been known but, because the fossils were deposited in high energy settings they are almost always disarticulated, so the fauna has not been described in detail. Recent intensive collection has revealed a diverse assemblage of material, including for the first time associated elements, which permits an evaluation of the faunal constituents at the locality. Although not diagnosable to a fine taxonomic level, sufficient apomorphies are present to identify representatives from numerous clades known from more complete specimens elsewhere. The evidence suggests a diverse fauna was present, including whatcheeriids and embolomeres. A single humerus previously had been attributed to a colosteid, but there is some uncertainty with this identification. Additional elements suggest the presence of taxa otherwise only known from the late Devonian. Depositional biases at the locality favor tetrapod fossils from larger individuals, but indirect evidence from trackways and tantalizing isolated bones evidences the presence of small taxa that remain to be discovered. The fossils from Blue Beach demonstrate that when windows into the fauna of ‘Romer’s Gap’ are found a rich diversity of tetrapods will be shown to be present, contra arguments that suggested this hiatus in the fossil record was due to extrinsic factors such as atmospheric oxygen levels. They also show that the early tetrapod fauna is not easily divisible into Devonian and Carboniferous faunas, suggesting that some tetrapods passed through the end Devonian extinction event unaffected.

Famennian Devonian to Mississippian Carboniferous Events of the Western USA

Uppermost Devonian (Famennian) to Lower Mississippian events of the western U.S.: Stratigraphy, sedimentology, chemostratigraphy, and detrital zircon geochronology

Authors:

Cole et al

Abstract:

Upper Devonian to Lower Mississippian strata in Utah and Montana record global events through this important interval in Earth history. Late Famennian strata of the Beirdneau, Leatham, and Pilot Shale formations in Utah, and Three Forks and Sappington formations in Montana, record widespread deposition of generally fine-grained siliciclastic and carbonate strata. Integration of sedimentology, physical stratigraphy, chemostratigraphy, and published biostratigraphy allows for the recognition of important disconformities and regional stratigraphic patterns. These enable the reconstruction of uppermost Devonian to lowermost Mississippian depositional, tectonic, and eustatic history of the region.

Carbon isotopic data allows for stratigraphic evaluation of the presence and absence of global bioevents of the Late Devonian, including the Annulata, Dasberg, and Hangenberg events, some of which are clearly recorded in hinterland deposits to the east in Colorado. While the Devonian–Mississippian boundary is also missing in our sections, a significant positive shift in δ13Ccarb in Lower Mississippian strata in Utah and Montana represents one of the largest positive δ13Ccarb isotope excursions of the Phanerozoic, linked to drawdown of atmospheric CO2 and glaciation in the Kinderhookian.

Detrital zircon spectra from latest Devonian to Early Mississippian strata of Utah and Colorado include populations representing derivation from the Mazatzal and Yavapai provinces, Middle Proterozoic anorogenic granite bodies, and a small influx of Grenville and presumed Appalachian–Caledonian grains. Minor Paleoproterozoic and Late Archean peaks in Utah are likely multiple generation grains originally derived from the Peace River Arch of northwestern Canada and recycled in Ordovician rocks of Nevada. These patterns in detrital zircon geochronological data reflect, in part, changes in sediment dispersal patterns due to tectonic and eustastic variability within the Antler foreland basin during the Devonian–Mississippian boundary interval. This variability also led to irregular spatial patterns of unconformity development, as well as complicated physical stratigraphic and chemostratigraphic architecture.

Early Seed Plants From Tournaisian Mississipian Carboniferous Argentina

Early seed plants from Western Gondwana: Paleobiogeographical and ecological implications based on Tournaisian (Lower Carboniferous) records from Argentina

Authors:

Prestianni et al

Abstract:

The oldest seed occurrences in Western Gondwana have been recognized in a new stratigraphic section located in Western Argentina (Precordillera Basin). Palynological evidence indicates an Early Mississippian (probably Tournaisian) age for this new succession. The two identified early seeds generas, Pseudosporogonites cf. hallei and Warsteinia sancheziae n. sp. were up to now considered as restricted to the Devonian of Laurussia. This finding suggests a dispersal of earliest spermatophytes between Laurussia and Gondwana during Devonian/Tournaisian times, thus accounting for the Rheic Ocean as a surmountable biogeographic barrier for continental biotas. Alternatively, contrasting biogeographic hypotheses dealing with early spermatophytes rising in paleotropics and then displacing herbaceous communities of non-spermatophytes typical from cool high latitudinal regions, are explored for explaining the recognized paleobiogeographical pattern. The new information supports a weak impact of the Devonian/Carboniferous biotic crisis on earliest seed plant diversity. Based on preliminary evidences of niches differentiation and ecological dynamics probably affected by wildfires, Tournaisian Gondwanan plant communities from high latitudes are interpreted as being more complex than previously thought, and more similar to those reported from Laurussia. In addition, their discovery in a sedimentary environment associated to glacigenic deposits, show that this new record might be linked to the coeval glacial age widely recorded elsewhere in Gondwana.

Edestus: The Weirdest Shark EVER?!

Edestus, the Strangest Shark? First Report from New Mexico, North American Paleobiogeography, and a New Hypothesis on its Method of Predation more

Author:

Itano

Abstract:

Two incomplete teeth of the chondrichthyan genus Edestus are reported. They were collected fromthe Gray Mesa Formation (Pennsylvanian, late Desmoinesian), Socorro County, New Mexico, in 1996.The better-preserved tooth belongs to Edestus sp. cf. E. heinrichi. The other cannot be identifiedbeyond the generic level. These are the first specimens of the genus known to be reported from NewMexico. The only other specimens known from the Rocky Mountain region are from Colorado. Boththe New Mexico and Colorado collections are from marine limestones. In North America, Edestus ismost common in marine black shales of the Illinois Basin, but to date has not been found in marinegray shales or limestones in the Appalachian Basin. The failure to find Edestus remains in the Appalachian Basin is probably the result of the precise timing and limited extent of marine incursionsinto that region. Edestus might have been less tolerant of restricted marine environments than otherchondrichthyans collected from Pennsylvanian deposits in the Appalachian Basin. The function of thesymphyseal tooth whorls of Edestus is obscure, inasmuch as their convex curvature makes them poorly-adapted to the “scissors” function proposed in some previous studies. Alternatively, it is pro-posed here that Edestus teeth were used to disable prey with a slicing action carried out with a verticalmotion of the head, with jaws fixed relative to each other, and not with a scissors-like action of thejaws moving relative to each other. This hypothesis is supported by the author’s observations of wearand damage on the teeth of the holotype of Edestus newtoni.  Helicoprion tooth whorls are similar to those of Edestus in that they contain sharp, serrated tooth crowns along the convex margin of the whorls and extend outside the oral cavity. The whorls might have functioned similarly to the mannerthat is hypothesized for Edestus,that is, to slash prey with a downward motion of the head, with jawsfixed. This proposed similarity in form and function would likely represent convergence
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Reassessing the Extent of Serpukhovian to Bashkirian Carboniferous Southwestern Gondwana's Glaciation

Reassessment of mid-Carboniferous glacial extent in southwestern Gondwana (Rio Blanco Basin, Argentina) inferred from paleo-mass transport of diamictites

Authors:

Gulbranson et al

Abstract:

Late Paleozoic glacial diamictites occur in many localities in western Argentina, indicating that the region was strongly affected by glaciation during the mid-Carboniferous (late Serpukhovian–early Bashkirian). In most instances these diamictites are found in steeply walled paleovalley settings in the Andean Precordillera. This study presents new data from a locality north of the Precordillera that suggests an additional, distinct, volume of ice existed in the region during the Carboniferous. The glacigenic diamictites in the Rio Blanco Basin were ultimately emplaced as gravity flows, precluding inferences of paleo-ice volume. Fold nose orientation and soft-sediment groove orientations within the diamictites indicate that the deposits were emplaced from north to south, suggesting that glacial ice was most likely not sourced from the proto-Precordillera at this locality, requiring the need for another ice center to the north of the basin. Diamictite facies indicates that the sediment was initially supplied to the study area by a warm-based glacier.

After Devonian Hangenberg Extinction, Fish Crushed Their Food

Trends in shell fragmentation as evidence of mid-Paleozoic changes in marine predation

Authors:

Salamon et al

Abstract:

Recent observations indicate that shell fragmentation can be a useful tool in assessing crushing predation in marine communities. However, criteria for recognizing shell breakage caused by durophagous predators versus physical factors are still not well established. Here, we provide data from tumbling and aquarium experiments to argue that physical and biotic processes lead to different patterns of shell damage, specifically that angular shell fragments are good indicators of durophagous predation. Using such angular shell fragments as a predation proxy, we analyze data from 57 European Paleozoic localities spanning the Ordovician through the Mississippian. Our results reveal a significant increase in angular shell fragments (either occurring as isolated valves or present in regurgitalites) in the Mississippian. The timing of this increase is coincident with the increased diversity of crushing predators as well as marked anti-predatory changes in the architecture and mode of life of invertebrate prey observed after the end-Devonian Hangenberg extinction (359 Ma). More specifically, the observed trend in shell fragmentation constitutes strong and independent confirmation of a recently suggested end-Devonian changeover in the primary method of fish predation from shearing to crushing. These results also highlight the important effect of extinction events, not only on taxonomic diversity, but also on the nature of predator-prey interactions.

Did a Great Flood Destroy the Native American Mississippian City of Cahokia?

One thousand years ago, on a floodplain of the Mississippi River near modern-day St. Louis, the massive Native American city known today as Cahokia sprang suddenly into existence. Three hundred years later it was virtually deserted.

The reasons for Cahokia's quick emergence and precipitous decline have been among the greatest mysteries in American prehistory, but new research suggests a possible cause of the city's demise: a catastrophic flood.

A team led by Samuel E. Munoz, a doctoral student at the University of Wisconsin, Madison, reported at the 2013 conference of the Geological Society of America that their study of sediment cores from a lake adjacent to the site of Cahokia reveals calamitous flooding of the area around 1200 C.E., just as the city was reaching its apex of population and power.

While analyzing cores from Horseshoe Lake, an oxbow lake that separated from the Mississippi River some 1,700 years ago, Munoz's team discovered a layer of silty clay 19 centimeters (7.5 inches) thick deposited by a massive ancient flood.

It's unlikely that the ancient floodwaters were high enough to inundate the ten-story mound at Cahokia's center, a structure now called Monk's Mound. (See "Cahokia: America's Forgotten City.") But a flood of such magnitude would have devastated croplands and residential areas, and may have made it impossible for a population numbering as many as 15,000 to continue inhabiting the area.

link.

Evidence of a Greenhouse Climate During the Visean-Serpukhovian in the Midst of the Carboniferous Ice Ages

A greenhouse interval between icehouse times: Climate change, long-distance plant dispersal, and plate motion in the Mississippian (late Visean-earliest Serpukhovian) of Gondwana

Authors:

Hermann W. Pfefferkorn, Vera Alleman and Roberto Iannuzzi

Abstract:

The late Paleozoic ice age (LPIA) is the closest example that can be compared with current climate conditions. Near the beginning of the LPIA fossil plants of Mississippian (late Visean to earliest Serpukhovian) age indicate a widespread frost-free climate in a wide belt on Gondwana indicating an interval of greenhouse conditions between the earlier Visean and later Serpukhovian icehouse times. This warm-temperate floral belt has been named the Paraca floral belt after the locality on the Peruvian coast where it was first recognized. The origin of this particular zono-biome was due to the interplay of (1) climate oscillations, (2) several kinds of long-distance plant dispersal within, between or through zono-biomes, and (3) plate motion. The Carboniferous age strata on the Paracas Peninsula in Peru serve as an example for an analysis of these large scale patterns through the analysis of local geology, paleobotany, and paleoecology. The processes observed during this time interval can serve as a model for long-distance plant dispersal at other times.

Scorpion is Gondwana's Oldest Known Land Animal

A postdoctoral fellow from Wits University has discovered the oldest known land-living animal from Gondwana in a remote part of the Eastern Cape. Dr Robert Gess, from the Evolutionary Studies Institute at Wits, discovered the 350 million year old fossilised scorpion from rocks of the Devonian Witteberg Group near Grahamstown. This unique specimen, which is a new species, has been called Gondwanascorpio emzantsiensis.

His discovery has been published in the peer reviewed journal African Invertebrate on Wednesday, 28 August 2013.

Explaining his discovery, Gess said that early life was confined to the sea and the process of terrestrialisation - the movement of life onto land - began during the Silurian Period roughly 420 million years ago. The first wave of life to move out from water onto land consisted of plants, which gradually increased in size and complexity throughout the Devonian Period.

This initial colonisation of land was closely followed by plant and debris-eating invertebrate animals such as primitive insects and millipedes. By the end of the Silurian period about 416 million years ago, predatory invertebrates such as scorpions and spiders were feeding on the earlier colonists of land.

By the Carboniferous period (350 million years ago), early vertebrates - our four-legged ancestors -had in turn left the water and were feeding on the invertebrates. Although we knew that Laurasia -the single northern landmass then comprising what is today North America and Asia - was inhabited by diverse invertebrates by the Late Silurian and during the Devonian, this supercontinent was at the time separated from the southerly positioned Gondwana by a deep ocean.

"Evidence on the earliest colonisation of land animals has up till now come only from the northern hemisphere continent of Laurasia, and there has been no evidence that Gondwana was inhabited by land living invertebrate animals at that time," explained Gess.

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