Were Heterodontosaurs Arboreal?

A newly described specimen of a tiny plant-eating dinosaur shows features indicating that it may have been able to climb around in branches -- an ability so far unknown in any dinosaurs except birds.

Dinosaurs were enormously successful vertebrates that dominated terrestrial ecosystems for almost the entire Mesozoic Era. The dinosaur family tree can be divided into three major branches: the theropods, mostly carnivorous bipeds (including birds); the sauropods, usually enormous long-necked herbivores; and the ornithischians, an incredibly diverse assemblage of beaked herbivores. Commonly known onithischians include (but are not limited to) armored dinosaurs, horned dinosaurs, bone-headed dinosaurs, and duck-bills. One of the earliest groups of ornithischians to appear in the fossil record are the heterodontosaurids, small bipeds recognizable by the long tusk-like teeth in their upper and lower beaks. Heterodontosaurids are known from the Upper Triassic to the Lower Cretaceous rocks in Africa, Asia, Europe, and North and South America and include the namesake Heterodontosaurus from the Early Jurassic of South Africa as well as the famous filament-covered Tianyulong from the Early Cretaceous of China.


In June, researchers described a new specimen of a heterodontosaurid found in Lower Jurassic rocks from Argentina dated to about 180 million years ago. The specimen, which consists of portions of the left and right foot, several toe bones, and some tail vertebrae comes from the Cañadón Asfalto Formation in near the town of Cerro Condor, Chubut Province. The authors think it’s likely that the remains belong to Manidens condorensis, a pigeon-sized heterodontosaurid found from the same location. Unfortunately the only known specimen of Manidens lacks its feet, so there are no overlapping parts that would make the assignment definitive.

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Evidence of Environmental Mosaic in Toarcian Jurassic China

A late Early Jurassic flora from Xilinhot Basin of Inner Mongolia,with discussions on coeval climate in China

Authors:

Shenghui et al

Abstract:

The flora from the Jurassic Hongqi Formation of the Xilinhot Basin,Inner Mongolia,North China,is composed of 37 species in 21 genera:Equisetites sp. and Neocalamites sp. of Equisetales;Hausmannia ussuriensis Kryshtofovich,H. leeiana Sze,Coniopteris bella Harris,C. sp.,Eboracia lobifolia(Phillips)Thomas,Todites williamsonia(Bronign.)Seward,Cladophlebis angutula (Heer)Fontaine,Cl. asiatica Chow et Yeh,Cl. cf. asiatica Chow et Yeh,Cl. haiburnensis(L. et H.)Bronigniart,Cl. hsiehiana Sze, Cl. lobifolia(Phillips)Bronigniart, Cl.ingens Harris,Cl.pseudoraciborskii Srebrodolskaja,Cl. shansiensis,Cl. scariosa Harris Sze and Cl. sp. nov. of Filicopsida;Anomozamites turkmenicus Burakova,Nilssoniopteris angustifolia Wang,Ptilophyllum contiguum Sze,Pterophyllum sp.,Nilssonia sp. nov. and Ctenis sp. of Cycadopsida;Ginkgoites ferganensis Brick,Ginkgoites hottonii (Sternb.)Heer, Phoenicopsis angustifolia Heer,Czekanowskia setacea Heer, Cz. latifolia Turutanova-Ketova and Sphenobaiera sp. of Ginkgopsida;Elatocladus sp.1, Elatocladus sp.2,Podozamites eichwaldi Schimper,Pityophyllum longifolium(Nath.)Moeller and Pityophyllum sp. of Coniferopsida and seed Carpolithus sp. The flora is characterized by abundant ferns and appearance of Coniopteris and Eboracia of the Dicksoniacea and some thermophilous elements. The thermophilous plants include dipteridaceous fern Hausmannia and Ptilophyllum of Bennettitales. The age of the flora is late Early Jurassic and most possibly the Toarcian. The age of the Hongqi Formation is chiefly late Early Jurassic and its upper part is possibly the early Middle Jurassic. The appearance of the climate sensitive plants,particularly the south-type(thermophilous)elements,indicates that the Xilinhot Basin was located in the warm temperate zone-subtropic zone during the late Early Jurassic. It was warmer than that of the early Early Jurassic and early Middle Jurassic,indicating a temperature raising event in the late Early Jurassic. Based on the palaeontological and sedimentary data, there existed 5 palaeoclimatic regions during the late Early Jurassic in China,namely the eastern Heilongjiang warm-cool climatic region,North China warm-temperate and warm-humid climatic region,central China tropic-subtropical semi-arid and semi-humid climatic region,central-southern China tropic-subtropical arid climatic region and the Tibet-western Yunnan tropical arid climatic region. The boundary between the warm-temperate warm-humid climatic region and the tropic-subtropical semi-arid and semi-humid climatic region was about 4-8 degrees of latitude northwards than both in the early Early Jurassic and early Middle Jurassic,also indicating a temperature arising event occurred in the late Early Jurassic. This climatic event most possibly happened in the Toarcian of Early Jurassic and is likely the response of the terrestrial ecological system to the Toarcian Oceanic Anoxic Event(T-OAE).

Dearcmhara shawcrossi: a new Toarcian/Bajocian Jurassic Ichthyosaur From Scotland

Ichthyosaurs from the Jurassic of Skye, Scotland

Authors:

Brusatte et al

Abstract:

Fossils of Mesozoic vertebrates are rare in Scotland, particularly specimens of marine reptiles such as plesiosaurs and ichthyosaurs. We describe a suite of ichthyosaur fossils from the Early to Middle Jurassic of Skye, which to our knowledge are the first ichthyosaurs from Scotland to be described and figured in detail. These fossils span approximately 30 million years, from the Sinemurian to the Bathonian, and indicate that ichthyosaurs were a major component of Scottish marine faunas during this time. The specimens include isolated teeth that could represent the most northerly known occurrences of the widespread Sinemurian species Ichthyosaurus communis, a characteristic component of the famous Lyme Regis faunas of England, suggesting that such faunas were also present in Scotland during the Early Jurassic. An associated humerus and vertebrae from Toarcian–Bajocian-aged deposits are named as a new genus and species of basal neoichthyosaurian, Dearcmhara shawcrossi. The taxonomic affinities of this taxon, which comes from a critical but poorly sampled interval in the fossil record, suggest that non-ophthalmosaurid neoichthyosaurians dominated European assemblages around the Early–Middle Jurassic boundary, and were later replaced by ophthalmosaurids, whose radiation likely took place outside Europe. Many of these specimens were collected by amateurs and donated to museum collections, a co-operative relationship essential to the preservation of Scotland’s fossil heritage.

Toarcian Jurassic Gregarious Tritylodontid (?) Therapsid Dunefield Trackways Suggest Colonial, Prairie Dog-like Lifestyle

TRACKWAYS OF A GREGARIOUS, DUNEFIELD-DWELLING, EARLY JURASSIC THERAPSID IN THE AZTEC SANDSTONE OF SOUTHERN NEVADA

Authors:

Rowland et al

Abstract:

We describe and interpret a tracksite in the Lower Jurassic Aztec Sandstone in Valley of Fire State Park, southern Nevada. The site contains approximately one hundred tracks of the ichnogenus Brasilichnium, arranged in twelve, subparallel trackways, all on the same foreset bedding plane. The Brasilichnium trackmaker was most probably a fossorial, tritylodontid therapsid. Sedimentologicial analyses indicate that the trackway surface is a wind-ripple horizon with a primary dip of about 25°, and that the animals climbed straight up the slip face of the dune. A combination of features leads us to conclude that the footprints were impressed into a crust of moist, cohesive sand, leaving two modes of preserved tracks: (1) shallow, well-defined tracks without associated sand crescents, and (2) deeper, less well defined tracks with associated sand crescents. We interpret this assemblage of tracks to record gregarious behavior in a mixed-age group of tritylodontid therapsids. In the correlative Navajo Sandstone, other researchers have documented the presence of complex networks of burrows concentrated in elevated mounds, reminiscent of colonies of North American prairie dogs. The Brasilichnium trackmaker is a good candidate to have excavated the burrows. Although we cannot directly associate the Brasilichnium trackmaker with the burrow complexes, we hypothesize that these gregarious, fossorial animals lived in prairie-dog–town–like colonies. This study supports the aridity food-distribution hypothesis, which posits that the patchy distribution of food resources in arid environments creates selective pressure for colonial behavior.

Multiple Isotopic Signatures in Toarcian Jurassic Oceanic Anoxic Event

Multiproxy geochemical analysis of a Panthalassic margin record of the early Toarcian oceanic anoxic event (Toyora area, Japan)

Authors:

Kemp et al

Abstract:

The early Toarcian oceanic anoxic event (OAE) was a significant palaeoenvironmental perturbation that led to marked changes in ocean chemistry and climate, and which also had a long-lasting impact on marine ecosystems. The global significance of the event has been recognised from the widespread occurrence of a ~ 3-7‰ negative excursion in the carbon-isotope (δ13C) composition of marine organic and inorganic matter and terrestrial plant material. This feature of the event is indicative of a pronounced perturbation to the global carbon cycle; an inference further supported by widespread evidence for seawater deoxygenation and elevated rates of organic carbon burial. Nevertheless, the precise palaeoenvironmental impacts of this event from sections outside of the Boreal and Tethyan realms are uncertain. Here, we present the results of a multiproxy geochemical study of an expanded record of the early Toarcian event from the northwest Panthalassa Ocean margin exposed in southwest Japan (Toyora area, Yamaguchi prefecture). Our results indicate that in the studied succession, organic matter enrichment persisted through the early Toarcian event, but elemental redox proxies do not support persistent seawater anoxia. Analyses of terrigenously derived major and trace element abundances coupled with sedimentological observations reveal an increase in coarse-grained sediment close to the onset of a ~ − 4‰ excursion in δ13Corg, and coincident with an inferred increase in terrestrial organic matter flux. These observations are consistent with previously published evidence for a marked strengthening of hydrological cycling and increased runoff that occurred contemporaneously with abrupt warming at the onset of the carbon isotope event.

The Impact of the Toarcian Jurassic Oceanic Anoxic Event on Pelagic Macrofauna

The impact of anoxia on pelagic macrofauna during the Toarcian Oceanic Anoxic Event (Early Jurassic)

Authors:

Caswell et al

Abstract:

Extreme environmental change during the Toarcian Oceanic Anoxic Event had widespread impacts on marine biota. This study provides new evidence, from the Yorkshire coast sections, UK, that the event was associated with periods of elevated fish and ammonite mortality. Using a synthesis of pelagic macrofaunal changes, benthic macrofaunal data and geochemical proxies we show that there are stratigraphical correlations between: (1) pelagic macrofaunal ranges and abundance, (2) benthic macrofaunal abundance, and (3) geochemical proxies that indicate deoxygenation. We identify eight stratigraphical intervals of differing character. Results suggest two major phases of relatively persistent deoxygenation with photic zone euxinia. The cyclostratigraphic timescale indicates that each phase lasted at least tens of thousands of years. Belemnite migration during the event probably resulted from increased seawater temperatures and low food supply similar to that observed for many marine taxa, including squid, within the present-day oceans.

Patterns & Timing of Toarcian Jurassic Nanfossil Crisis

Pattern and timing of the Early Jurassic calcareous nannofossil crisis

Author:

Clemence

Abstract:

The Toarcian calcareous nannofossil crisis associated with the early Toarcian Oceanic Anoxic Event (T-OAE) in the Early Jurassic period is thought to represent one of the most important biocalcification crises during the Mesozoic, occurring simultaneously with a profound disturbance of the carbon cycle. However, the causes are still under debate, particularly with regard to the pattern, timing of the biocalcification crisis, relative roles of intrinsic and extrinsic processes as drivers of the crisis, and also causal mechanisms of the T-OAE.

In this study, a new quantification of Toarcian calcareous nannofossil abundance and size is presented for the Sancerre borehole (Paris Basin, France). Beyond the recognition of a severe biocalcification crisis defined by the major drop in abundance, and the reduction in size of the most important pelagic carbonate producer Schizosphaerella punctulata, for the first time, this study proposes an insight into the pace and timing of the nannoplankton crisis. At Sancerre, the carbonate production of the lower Toarcian sediments previously attributed to obliquity forcing of climate allows to estimate a duration of ~ 210 kyr for the biocalcification crisis and of ~ 120 kyr for the shift towards lower carbon isotope values. The onset of the biocalcification crisis marked by a fertility event lasted ~ 60 kyr, and the calcium carbonate values remained low for ~ 150 kyr; the subsequent recovery of carbonate and nannoplankton lasted ~ 60 kyr and greater than 550 kyr, respectively. Additionally, a link between the biocalcification crisis, the seawater palaeotemperature, and the carbon isotope steps can be demonstrated. This covariance provides compelling evidence of fundamental change in the response of the climatic warming and the carbon cycle systems triggering the biocalcification crisis. These observations indicate that the biocalcification crisis can be regarded as a direct or indirect consequence of a global warming. Moreover, a deficiency of the biological pump is proposed here as a complementary casual mechanism for explaining the negative carbon-isotope excursion.

Nanofossil Evidence of the Early Toarcian Cretaceous Oceanic Anoxic Event

The Early Toarcian Oceanic Anoxic Event in the External Subbetic (Southiberian Palaeomargin, Westernmost Tethys): Geochemistry, nannofossils and ichnology

Authors:

Reilid et al

Abstract:

The analysis of macroinvertebrates, trace fossils, calcareous nannofossils and geochemistry from Pliensbachian to Lower Toarcian deposits of the Subbetic (Southern Spain) allows us to interpret the incidence of the Toarcian Oceanic Anoxic Event (T-OAE) in the boundary between the Tethys and the Hispanic Corridor. Trace fossils from the marl-limestone rhythmite (Upper Pliensbachian to Lower Toarcian) indicate an oxygenated bottom. A dark marly interval occurs above a fossil-rich condensed surface with a negative excursion of δ18O, interpreted as evidence of the Early Toarcian transgression and a climate warming. The carbon cycle perturbation is recorded by decreasing CaCO3 content and the negative excursion of δ13C at the base of the Serpentinum Zone, NJT 6 nannofossil Zone. The barren interval for nektonic and benthic organisms at the beginning of the Serpentinum Zone confirms the oxygen restricted conditions in the sea-floor. Environmental conditions were unfavourable for the development of calcareous nannoplankton, as attested by the drop in absolute abundances. The deep photic zone seemed to be particularly hostile to phytoplankton, as shown by the decrease in relative abundance of the deep-dweller Mitrolithus jansae, related to shoaling of the oxygen minimum zone in the water column. Increasing values of redox sensitive elements and total organic carbon, as well as the record of pyrite framboids < 5 μm size, confirm the anoxic conditions (probably euxinic conditions in any moment) at the base of the dark marly interval (NJT 6). The return to oxic or dysoxic conditions is confirmed by the record of fossil-poor marls with scarce macroinvertebrates and microfossils, as well as the recovery of trace fossils mainly (low-oxygen tolerant Chondrites tracemakers). Increasing abundance of calcareous nannofossils and deep-dweller M. jansae indicate ameliorated environmental conditions in the water column. Geochemistry supports the recovery of carbonate production (increasing CaCO3) and oxygen availability (decrease of TOC and redox sensitive elements).

Toarcian Jurassic Anoxic Events (Mass Extinction?) Driven by Karoo Volcanism?

Effects of Karoo–Ferrar volcanism and astronomical cycles on the Toarcian Oceanic Anoxic Events (Early Jurassic)

Authors:

Ikeda et al

Abstract:

One of the most profound environmental changes in the Mesozoic took place during Pliensbachian–Toarcian (Early Jurassic), including oceanic anoxia (Toarcian Oceanic Anoxic Event; T-OAE). The T-OAE is thought to have been caused by increased atmospheric CO2 triggered by Karoo–Ferrar volcanism. This idea, however, remains debated, primarily due to uncertainties in their age constraints of the relevant sedimentary sequences. To examine their temporal relationships, herein, we provide the astronomical time scale of the Lower Jurassic deep-sea bedded chert sequences from the pelagic Panthalassa superocean, which are exposed in the Inuyama area, central Japan. A 405-kyr tuned astrochronology, anchored to the end-Triassic extinction as 201.4 ± 0.2 Ma (Ikeda and Tada, 2013), allows us to constrain the ages of two black bedded cherts (T-OAE1 and T-OAE2). The ages of these T-OAEs overlap U–Pb ages of Karoo volcanic rocks. T-OAE in the European region is also synchronous with the Karoo–Ferrar volcanism, based on radiolarian and ammonite biostratigraphic correlation. These temporal relationships support the potential impact of Karoo–Ferrar volcanism on T-OAEs on a global scale. On the other hand, the onset of T-OAEs occur at the maxima of ~ 40 kyr, ~ 100 kyr, and 405 kyr cycles of chert thickness variation. The termination of T-OAEs and the recovery to oxic conditions in pelagic ocean coincide with the minima of ~ 40 kyr, ~ 100 kyr, and 405 kyr cycles of chert thickness. Moreover, the termination of final black chert and grey chert deposition coincide with the minima of ~ 1800 kyr cycles of chert thickness. These temporal relationships imply that orbital-scale productivity cycles were important in controlling the onset and termination of T-OAEs through the carbon cycle dynamics, which have been already amplified by Karoo–Ferrar volcanism.

Ferns Stole 'neochrome' Gene From Hornworts During the Toarcian Jurassic 179 Million Years ago

During the age of the dinosaurs, the arrival of flowering plants as competitors could have spelled doom for the ancient fern lineage. Instead, ferns diversified and flourished under the new canopy -- using a mysterious gene that helped them adapt to low-light environments.

A team led by Duke University scientists has pinpointed the curious origins of this gene and determined that it was transferred to ferns from a group of unassuming moss-like plants called hornworts. The findings were announced today, April 14, in the Proceedings of the National Academy of Sciences.

For years, researchers have suspected that a gene called neochrome played a role in the evolution of ferns. Neochrome is a hybrid of two other plant genes which code for photoreceptor proteins that sense blue and red light.

"Neochrome is a 'chimeric' gene," said Fay-Wei Li, lead author and Ph.D. student in Duke's biology department. It produces a photoreceptor that senses both blue and red light, affording ferns a unique advantage in forests shaded by flowering plants. "Most plants sense and grow toward blue light, but under the canopy, the filtered light spectrum has more red light than blue."

"Neochrome helped ferns to 'see' better," Li said. What hasn't been crystal clear is the gene's origin. Li set out to investigate its evolution by systematically combing through plant genomes from the Duke Herbarium and 1000 Plants Initiative.

Neochrome turned up in a surprising place: the genomes of hornworts, a damp-loving plant group related to mosses.

Three scenarios could have explained how the gene came to be shared by ferns and hornworts: 1) a common ancestor that had the gene; 2) independent evolution of the gene in both groups; or 3) a process called horizontal gene transfer, which ferried neochrome from one group to the other.

To sort out these theories, the team looked not only at the evolutionary relationships of land plants and algae, but also at how all of their light-sensitive genes were related.

Ferns and hornworts diverged in evolution 400 million years ago. If neochrome came from a common ancestor, it would have been passed on to many other plant families, too. But then it had to have been lost in all but the ferns, since no seed plants still have it. The analysis also didn't support the idea that an unusual gene like neochrome evolved independently in both hornworts and ferns.

What the scientists found instead was strong evidence that the fern version of neochrome descended from the hornwort version. By looking at sequence changes in the gene's various spellings, they constructed a family tree of light-sensitive genes, in which fern neochrome "nested" neatly within the hornwort lineage. The analysis also showed that the gene versions separated about 179 million years ago.

Only one mechanism could explain how the gene hopped from hornworts to ferns so long after the lineages themselves diverged: horizontal gene transfer. But researchers have only just begun to explore how this occurs in plants.

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Toarcian Jurassic Fossil Fern Preserves Chromosomes, Mitosis in Action

Researchers from Lund University and the Swedish Museum of Natural History have made a unique discovery in a well-preserved fern that lived 180 million years ago. Both undestroyed cell nuclei and individual chromosomes have been found in the plant fossil, thanks to its sudden burial in a volcanic eruption.

The well-preserved fossil of a fern from the southern Swedish county of Skåne is now attracting attention in the research community. The plant lived around 180 million years ago, during the Jurassic period, when Skåne was a tropical region where the fauna was dominated by dinosaurs, and volcanoes were a common feature of the landscape. The fossilised fern has been studied using different microscopic techniques, X-rays and geochemical analysis. The examinations reveal that the plant was preserved instantaneously, before it had started to decompose. It was buried abruptly under a volcanic lava flow.

"The preservation happened so quickly that some cells have even been preserved during different stages of cell division", said Vivi Vajda, Professor of Geology at Lund University.

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Significant Climate Change Observed for Toarcian Jurassic in Paris Basin

Continental weathering and climatic changes inferred from clay mineralogy and paired carbon isotopes across the early to middle Toarcian in the Paris Basin

Authors:

Hermoso et al

Abstract:

Lower Toarcian strata (Lower Jurassic) have been extensively studied with a view to understanding the oceanographic, climatic and biological processes that drove the Earth’s system into an Oceanic Anoxic Event (OAE). For this time period, the evolution of the European marine seaways is now relatively well constrained owing to multiple geochemical studies, but investigations regarding climatic trends in the continental realm remain sparse. In the present study, we test the clay mineralogy as a continental climate-sensitive proxy in the well-documented Sancerre core (southern Paris Basin). We compare variations in the kaolinite content with pCO2 fluctuations (derived from paired carbon isotopes; ∆13C = δ13Ccarb – δ13Corg), taking advantage of the detailed chemostratigraphic, palaeoenvironmental and sequence stratigraphy frameworks established for this core material. The results indicate a substantial decrease in kaolinite abundance at the end of the Pliensbachian, which is compatible with a long-term diminution in continental weathering and an inferred temperature decrease. The early Toarcian, prior to the carbon cycle perturbation and deposition of black shale facies, remained relatively cold with minima in both the proportion of kaolinite and reconstructed pCO2. The mineralogical and geochemical responses across the prominent negative carbon isotope excursion (CIE) itself are not univocal. The first of four steps that compose the negative limb of the CIE at Sancerre is associated with decreased kaolinite and pCO2, and increased carbonate oxygen isotope ratios. Taken together, these trends are compatible with a transient cooling phase immediately preceding the onset of black shale deposition. Conversely, the subsequent steps are marked by substantial enrichment in kaolinite that matches increased osmium isotope ratios measured in Yorkshire, providing compelling evidence for rapid increases in continental weathering and riverine runoff forced by intensification of greenhouse conditions during the CIE. Relaxation in the intensity of continental weathering, as suggested by resumed low kaolinite abundance is seen immediately after the cessation of CO2 input (after the fourth step of the CIE). The interval spanning the upper portion of the early Toarcian and the middle Toarcian records a subsequent long-term increase in the proportion of kaolinite synchronous with significant clay enrichment of the sediment. Continued greenhouse conditions, even after the recovery from the carbon isotope perturbation and “regional” black shale deposition, are likely related to sustained CO2 emission by Karoo-Ferrar volcanism through the considered interval.

Toarcian Jurassic Oceanic Anoxic Event Evidence From Foraminifera and Ostracods Isotopic Evidence

Stable isotopes on foraminifera and ostracods for interpreting incidence of the Toarcian Oceanic Anoxic Event in Westernmost Tethys: Role of water stagnation and productivity

Author:

Matías Reolid

Abstract:

The analysis of δ13C and δ18O from whole rock and the shells of selected foraminifera (Lenticulina and Dentalina) and bairdioid ostracods from Lower Toarcian of the South Iberian Palaeomargin (Western Tethys) is presented with the aim of improving knowledge of the processes and the environmental effects of the Toarcian Oceanic Anoxic Event. In addition, isotopic data are compared with geochemical redox and palaeoproductivity proxies. The microhabitat affected δ13C values, δ13CLenticulina generally being lower than δ13CDentalina due to more depleted 13C values for sediment pore-water in the deep infaunal microhabitat. The lowest values of δ13C (lower part of Serpentinum Zone) happen during suboxic conditions, as indicated by redox proxies, low diversity and abundance of foraminifera and higher TOC values. The fine-grained, organic rich sediments allow for conditions favouring pore-water dissolved inorganic carbon that is depleted in 13C with respect to that of the bottom sea-water, particularly during the suboxic conditions. The δ13C of potential deep infauna (Lenticulina) reflects the oxygen restricted conditions better than shallow infauna (Dentalina) and whole sediment. Regarding δ18O, values from bulk rock present stronger fluctuations and lower values than δ18ODentalina and δ18OLenticulina. The stratigraphic differences between δ18ODentalina and δ18OLenticulina correspond to vital effects, since no important fluctuations in temperature occurred in the bottom sea-water, as deduced from the absence of peaks and stratigraphic trends in the interval studied. The δ18O values do not allow us to infer temperature changes related to the Toarcian Oceanic Anoxic Event in this part of the palaeomargin.

Evidence of the Toarcian Jurassic Oceanic Anoxic Event in Greece

The Toarcian Oceanic Anoxic Event in the Ionian Zone, Greece

Authors:

Kafousia et al

Abstract:

The Early Jurassic was characterized by a global disturbance of the carbon cycle known as the Toarcian Oceanic Anoxic Event (T-OAE). This event is recorded worldwide by a negative excursion in marine and terrestrial carbon-isotope ratios, typically interrupting an overarching positive trend attributed to large-scale burial of marine organic matter under oxygen-depleted conditions. The negative excursion is attributed to introduction of isotopically light carbon into the ocean–atmosphere system. Three sections from the Ionian Zone in Greece have been analysed in terms of biostratigraphy, Total Organic Carbon (TOC), CaCO3, δ13Ccarb, δ18Ocarb and δ13Corg. On the basis of bio- and chemostratigraphy, the age of Pliensbachian–Toarcian formations from the Ionian Zone in Greece has been refined and the geochemical signature of the T-OAE recognized. All sections illustrate the characteristic negative excursion in carbon isotopes from both carbonates and organic matter and, in only one locality, a positive excursion has also been recorded. The recognition of the T-OAE in this part of the Tethyan continental margin offers additional information on the global impact and amplitude of this important Jurassic palaeoceanographic event.

Evidence for Caudal Fins in Plesiosaurs From the Toarcian Jurassic

MORPHOLOGY OF THE CAUDAL VERTEBRAE IN RHOMALEOSAURUS ZETLANDICUS AND A REVIEW OF THE EVIDENCE FOR A TAIL FIN IN PLESIOSAURIA

Author:

Adam S. Smith

Abstract:

The holotype of the large plesiosaurian Rhomaleosaurus zetlandicus from the Toarcian (Lower Jurassic) of England comprises an almost complete skeleton, including the caudal vertebral series. The osteology of the tail is described and two morphological characteristics are interpreted as evidence for a caudal fin in Rhomaleosaurus: 1. A distinct node consisting of two relatively anteroposteriorly shortened vertebrae; and 2. Laterally compressed terminal caudal centra. This inference is based on osteological correlates derived from other marine reptile groups that possessed a vertically oriented bilobed dermal tail fin in life (ichthyosaurs, thalattosuchian crocodylomorphs, and mosasaurs). This corroborates evidence from other plesiosaurian taxa and suggests that a caudal fin may have been widespread among plesiosaurians, with implications for locomotion and behavior.

Benthic Faunal Reactions to Climate Change During the Toarcian Jurassic

The Impact of Global Warming and Anoxia on Marine Benthic Community Dynamics: an Example from the Toarcian (Early Jurassic)

Authors:

1. Silvia Danise (a)
2. Richard J. Twitchett (a)
3. Crispin T. S. Little (b)
4. Marie-Emilie Clémence (a)

Affiliations:

a. School of Geography, Earth and Environmental Sciences, Plymouth University, Plymouth, United Kingdom

b. School of Earth and Environment, University of Leeds, Leeds, United Kingdom

Abstract:

The Pliensbachian-Toarcian (Early Jurassic) fossil record is an archive of natural data of benthic community response to global warming and marine long-term hypoxia and anoxia. In the early Toarcian mean temperatures increased by the same order of magnitude as that predicted for the near future; laminated, organic-rich, black shales were deposited in many shallow water epicontinental basins; and a biotic crisis occurred in the marine realm, with the extinction of approximately 5% of families and 26% of genera. High-resolution quantitative abundance data of benthic invertebrates were collected from the Cleveland Basin (North Yorkshire, UK), and analysed with multivariate statistical methods to detect how the fauna responded to environmental changes during the early Toarcian. Twelve biofacies were identified. Their changes through time closely resemble the pattern of faunal degradation and recovery observed in modern habitats affected by anoxia. All four successional stages of community structure recorded in modern studies are recognised in the fossil data (i.e. Stage III: climax; II: transitional; I: pioneer; 0: highly disturbed). Two main faunal turnover events occurred: (i) at the onset of anoxia, with the extinction of most benthic species and the survival of a few adapted to thrive in low-oxygen conditions (Stages I to 0) and (ii) in the recovery, when newly evolved species colonized the re-oxygenated soft sediments and the path of recovery did not retrace of pattern of ecological degradation (Stages I to II). The ordination of samples coupled with sedimentological and palaeotemperature proxy data indicate that the onset of anoxia and the extinction horizon coincide with both a rise in temperature and sea level. Our study of how faunal associations co-vary with long and short term sea level and temperature changes has implications for predicting the long-term effects of “dead zones” in modern oceans.

Signals for Multiple Pulses in Early Toarcian Jurassic Extinction

The early Toarcian (early Jurassic) ostracod extinction events in the Iberian Range: The effect of temperature changes and prolonged exposure to low dissolved oxygen concentrations

Author:

1. Carmen Arias (a)

Affiliation:

a. Departamento de Paleontología e Instituto de Geociencias (IGEO), Facultad de Ciencias Geológicas, Universidad Complutense de Madrid, 28040-Madrid, Spain

Abstract:

The early Toarcian extinction event, once regarded as spanning the late Pliensbachian-early Toarcian boundary period, actually occurred in two distinct phases in the early Toarcian of the Iberian Range. The first episode occurred in the Mirabile Subzone, Tenuicostatum Zone and is characterized by the disappearance of about 12% of ostracod species and one suborder, the Metacopina (Superfamily Healdioidea). This study shows that this suborder disappears during stratigraphical intervals that are considered to be representative of low oxygen conditions in the Iberian Range. The collapse of marine ecosystems (affecting up 40% of ostracod species) in the Elegantulum Subzone, Serpentinum Zone was most likely triggered by a sudden and widespread lethal increase in seawater temperature. These combined processes of oxygenation and temperature change are considered to be responsible for the profound changes in marine environments that resulted in the early Toarcian ostracod extinction in the Iberian Range.

More Evidence of a Toarcian Mass Extinction: Ammonites Had Low Diversity in Toarcian Jurassic Northern NeoTethys of Cacasian Russia

Spatial heterogeneity of the Early–Middle Toarcian (Jurassic) ammonite diversity and basin geometry in the Northwestern Caucasus (southwestern Russia; northern Neo-Tethys)

Author:

1. Dmitry A. Ruban (a)

Affiliation:

a. Division of Mineralogy and Petrography, Geology and Geography Faculty, Southern Federal University, Zorge Street 40, Rostov-na-Donu, 344090, Russian Federation

Abstract:

Palaeontological and geological information from the Northwestern Caucasus, a large region in southwestern Russia, allows to evaluate the spatial heterogeneity of the Early–Middle Toarcian ammonite diversity and its possible controls. The total number of ammonite species and genera is calculated for four time slices, which correspond to the D. semicelatum, H. falciferum, H. bifrons, and H. variabilis zones, in each of ten areas distinguished within the study region. These areas differ by the ammonite diversity, which indicates heterogeneity. The latter persisted through the entire Early–Middle Toarcian. This heterogeneity was relatively low in the beginning of the Toarcian, when the total regional diversity of ammonites was minimal. Long- and short-term landward shoreline shifts facilitated spatial distribution of ammonites and increase in their taxa number. Shallow-marine palaeoenvironments tended to sustain a higher diversity than those deep-marine, and, therefore, changes in the basin depth were also responsible for the observed spatial heterogeneity of the ammonite diversity. Interestingly, a more or less similar diversity dynamics is established in the areas of the Northwestern Caucasus. The distribution of ammonites in the study region indicates that these invertebrates migrated to there from the open sea(s) stretched along the northern margin of the Neo-Tethys Ocean. Results of the present analysis also imply that the mass extinction might have been responsible for the low diversity of ammonites (observed in the entire region and its particular areas) in the beginning of the Toarcian.

Pliensbachian–Toarcian Jurassic Extinction Was a Phased Event

The Pliensbachian–Toarcian (Early Jurassic) extinction, a global multi-phased event

Authors:

1. Andrew H. Caruthers (a)
2. Paul L. Smith (a)
3. Darren R. Gröcke (b)

Affiliations:

a. Department of Earth Ocean and Atmospheric Sciences, University of British Columbia, Room 2020 Earth Sciences Building, 2207 Main Mall, Vancouver British Columbia V6T 1Z4, Canada

b. Department of Earth Sciences, Durham University, South Road, Durham DH1 3LE, UK

Abstract:

During the Pliensbachian–Toarcian of Early Jurassic, there is a well-known second order marine extinction that is observable at the species and genus levels. Ammonite diversity data from successions throughout Europe and parts of the Arctic suggest that this extinction may have been multi-phased with diversity declining over six separate intervals. The main-phase of decline begins at the Pliensbachian–Toarcian boundary and extends into the Lower Toarcian, to a level that is correlative with the Tenuicostatum / Serpentinum Zone boundary. To date, only the main-phase of extinction has been demonstrated as being global in extent and affecting multiple taxonomic groups. This multi-phased extinction has been attributed to regional and global controlling mechanisms that are associated with the Volcanic Greenhouse Scenario which links the eruption of the Karoo–Ferrar large igneous province (LIP) to global warming and mass extinction.

We compare stratigraphic ranges of ammonite and foraminiferal species in Pliensbachian–Toarcian successions of western North America to the record in Europe and parts of the Arctic in order to test the geographic extent of the multiple phases of extinction. Our results show six intervals of species level decline that correlate with those recognized in Europe: 1) middle of the Lower Pliensbachian (middle Whiteavesi–middle Freboldi Zones), 2) middle of the Upper Pliensbachian (upper Kunae–lower Carlottense Zone), 3) Pliensbachian / Toarcian boundary into the Lower Toarcian (upper Carlottense–middle Kanense Zones), 4) Middle Toarcian (upper Planulata–lower Crassicosta Zones), 5) upper Middle–lower Upper Toarcian (middle Crassicosta–Hillebrandti Zones) and 6) Upper Toarcian (lower Yakounensis Zone).

Recognition of this multi-phased event in three separate ocean basins (paleo Pacific, paleo Arctic, and Tethys Oceans), in at least two taxonomic groups, greatly expands the known geographic extent of this multi-phased event and argues for a controlling mechanism that is global in its reach. In relation to the Volcanic Greenhouse Scenario, our study shows that four of the six pulses of extinction occur within the main-phase of Karoo magmatism. The decline in the Early Pliensbachian, previously thought to be separate from this event, occurs within error range of the onset of Karoo magmatism and the decline in the Late Toarcian coincides with the later stages of magmatism. These observations extend the known duration of this multi-phased extinction event to the Early Pliensbachian and support the Volcanic Greenhouse Scenario, specifically the eruption of the Karoo–Ferrar LIP, as a preeminent factor driving the multi-phased extinction of the Pliensbachian–Toarcian.

Very Large Toarcian Jurassic English Pterosaur Found

The humeral head (anterodorsal view) and the scapulocoracoid (medial view) of NHMUK R36634. Scale bar = 10 mm

A pterosaur humerus and scapulocoracoid from the Jurassic Whitby Mudstone Formation, and the evolution of large body size in early pterosaurs

Authors:

1. Michael O'Sullivan (a)
2. David M. Martill (a)
3. David Groocock (b)

Affiliations:

a. School of Earth and Environmental Sciences, University of Portsmouth, Portsmouth, PO1 3QL, UK

b. 77 Osborne Terrace, Stacksteads, Bacup, Lancashire OL1 8JY, UK

Abstract:

Early Jurassic pterosaurs are rare and display low diversity with only three well known genera for a period of ~21 million years duration. The Hettangian-Pliensbachian Dimorphodon reached a wingspan estimated at only 1.3 m, while the Lower Toarcian forms Dorygnathus and Campylognathoides reached wings spans of 1.8 m. Here we describe a new specimen of Toarcian pterosaur from the north east coast of England that may have achieved an estimated wingspan between 1.6 and 3.2 m.