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.

Alcidedorbingya inopinata: the Oldest Known Pantodont Eutherian From Danian Paleocene Paleogene Bolivia

Alcidedorbignya inopinata, a basal pantodont (Placentalia, Mammalia) from the early Palaeocene of Bolivia: anatomy, phylogeny and palaeobiology

Authors:

Muizon et al

Abstract:

The study of exceptional remains (several skulls and a complete skeleton) of a 65 MY old placental mammal from Bolivia, provides a good understanding of the cranial anatomy, biology and evolution of the first mammals which lived in South America just after the large dinosaurs disappeared, 66 MY ago. This mammal is a Pantodont named Alcidedorbingya, in honour of Alcide d’Orbigny, famous naturalist voyager of the Museum during the XIXth century. Pantodonts constitute a group of mammals from the beginning of the Tertiary, which disappeared 40 MY ago. They lived essentially in northern continents (China, North America, and Europe). They were of small (rabbit) to large size (cow) and were omnivorous. Alcidedorbignya is the only austral pantodont, the oldest, and the smallest known.

The CT scanner of the MNHN allows the authors, a reconstruction of the arterial and venous passageways of the basicranium, thus approaching an ancestral pattern of blood circulation of the first placental mammals. The complete skeleton of Alcidedorbignya, was also CT scanned, allowing virtual reconstructions of several life positions. Alcidedorbignya was terrestrial, but also capable of a bipedal position on its hind limbs and of climbing as is observed in the Recent squirels. This ability allowed Alcidedorbignya to escape the numerous crocodiles, which lived with it in a large Amazonian-like alluvial plain.

These results have been obtained thanks to the unprecedented completeness of the specimens, taking into account their geological age, in which the most common remains are only isolated teeth.

Evidence of Reduced Export Productivity Supporting Living or Heterogeneous Ocean Hypotheses for KT/K-Pg mass Extinction

Evidence for reduced export productivity following the Cretaceous/Paleogene mass extinction

Authors:

Esmeray-Senlet et al

Abstract:

The Cretaceous/Paleogene (K/Pg) mass extinction was associated with a collapse in the carbon isotopic (δ13C) gradient between planktonic and benthic foraminifera and a decrease in bulk carbonate δ13C values. These perturbations have been explained by several hypotheses: global collapse of primary productivity (Strangelove Ocean); greatly reduced export but not primary productivity (Living Ocean); little or no reduction in export productivity (Resilient Ocean); and geographic heterogeneity in the change of export productivity (Heterogeneous Ocean). We tested primary vs. export productivity changes in the paleoshelf of New Jersey, where δ13C values and organic carbon accumulation rates can distinguish among different ocean responses. On the shelf, the K/Pg boundary is associated with a ~2.5‰ δ13C decrease in bulk carbonate, a ~0.8‰ δ13C decrease in organic carbon, a collapse of the surface to bottom δ13C gradient, and a drop in organic carbon percentage. We interpret an early Danian ~1.0‰ planktonic foraminiferal δ13C gradient, a ~0.75‰ cross-shelf benthic foraminiferal δ13C gradient, and a drop in carbon accumulation rates to reflect the presence of active primary but limited export productivity, consistent with the Living Ocean hypothesis. We evaluated interbasinal deep-sea benthic foraminiferal δ13C gradients between the Pacific (Site 1210) and the Atlantic (Site 1262) oceans as a proxy for changes in export productivity. The interbasinal δ13C gradient was reduced after the mass extinction, suggesting a reduction in global export productivity. Although our data support the Living Ocean hypothesis, evidence from paleo-upwelling zones shows significant export productivity, indicating spatial heterogeneity in the wake of the K/Pg mass extinction (Heterogeneous Ocean).

Evidence the First Few Thousand Years After Chicxulub Impact the Climate Cooled

Palynological evidence for prolonged cooling along the Tunisian continental shelf following the K–Pg boundary impact

Authors:

Velekoop et al

Abstract:

The Cretaceous–Palaeogene (K–Pg) boundary mass extinction event is related to major global environmental changes resulting from a large extraterrestrial impact. Organic-walled cyst-producing marine dinoflagellates (dinocysts) survived the K–Pg mass-extinction relatively unscathed, making them ideally suited for reconstructing these environmental changes. So far, one of the best dinocyst records available is from the K–Pg boundary Global Stratotype Section and Point (GSSP) at El Kef (NW Tunisia). There, the dinocyst record shows major fluctuations across the boundary, likely reflecting strong responses to environmental changes. These fluctuations have so far not been confirmed by other studies. Therefore, in this study we performed a high-resolution marine palynological study on a closely spaced sample set from the Elles section, some 75 km south of El Kef, in order to generate a palaeoenvironmental and palaeoclimatic record across the K–Pg boundary to allow verification and refinement of earlier reported environmental changes. To better constrain the reconstructions based on qualitative biotic proxies we employed the quantitative sea surface temperature proxy TEX86. Unfortunately, the TEX86 proxy record of the studied section is compromised because of post-depositional oxidation. However, the diverse dinocyst assemblages at Elles show strong fluctuations similar to the El Kef record, therefore confirming the earlier recorded signals, showing rapid, regionally consistent changes. These records imply that the latest Cretaceous was characterized by a gradual cooling trend and the onset of relative sea level fall. Within the immediate post-extinction interval, in the first thousands of years after the impact, dinocyst assemblages reveal multiple incursions of higher-latitude dinocyst species implying repeated pulses of cooling. These results signify that the earliest Danian climatic and environmental conditions were relatively unstable across the Tunisian shelf.

An Abrupt Palaeoenvironmental Change Across the Danian/Selandian Paleocene Paleogene

Integrated bio-chemostratigraphical correlations and climatic evolution across the Danian–Selandian boundary at low latitudes

Authors:

Storme et al

Abstract:

The Global Boundary Stratotype Section and Point for the base of the Selandian Stage is defined in the Zumaia section (Spain) at an abrupt change in lithology (base of Itzurun Formation), which coincides with the onset of a negative carbonate carbon isotope shift. However, this lithological change is not always very well expressed in other sections. In order to document the stratigraphic position of the Danian/Selandian boundary (DSB) on a more global scale, we have investigated three sections across the DSB, the Zumaia reference section (GSSP), the Loubieng section (auxiliary DSB reference section, France) and the Sidi Nasseur section (Tunisia). The Danian/Selandian boundary interval is subdivided and correlated throughout low latitudes, from the Altlantic Bay of Biscay to the Southern Tethys, on the basis of seven calcareous nannofossil and planktonic foraminiferal events (E-events). The base of the Selandian is proved to coincide with the end of the Braarudosphaera acme, which correlates with the lowest consistent occurrence (LCsO) of Lithoptychius aff. bitectus (= Fasciculithus janii sensu Steurbaut and Sztrákos, 2008) (event E4), but which is slightly posterior to the second radiation of the fasciculiths, up to now considered to represent the primary correlation tool of the DSB. A short-term δ13Corg negative excursion, associated with an increase in pCO2 is recorded at the very base of the Selandian. It is interpreted as a short period of global warming (hyperthermal), the duration of which is estimated at ~ 30 kyr. It is followed in all the three studied sections by a long-term decoupled carbon isotope event, marked by increasing δ13Corg and decreasing δ13Ccarb values. It may reflect a period of climatic cooling of a few 100 kyr, interpreted as a possible precursor of the global cooling event, marking the late Paleocene in the North Atlantic realm. The integration of the biostratigraphic and the isotope data indicates major differences in sedimentation rates during the early Selandian in the studied sections, but there is no evidence of substantial breaks in sedimentation in any of the sections during this interval. The lithological shift at the base of the Selandian points to an abrupt palaeoenvironmental reorganisation, although our integrated bio-chemostratigraphical investigation does not allow for estimating its duration nor the presence of a hiatus at that time.

Complete Marine Maastrichtian-Danian Succession at Stevns Klint Strongly Supports Abrupt Faunal Turnover at Cretaceous-Paleogene Boundary

Marine macrofossil communities in the uppermost Maastrichtian chalk of Stevns Klint, Denmark

Authors:

Hansen et al

Abstract:

Three successive marine habitats and their benthic macrofossil communities have been recognized and assessed in the uppermost Maastrichtian chalk of Stevns Klint, Denmark. The mound-bedded lower Sigerslev Member was deposited below the photic zone under the influence of persistent, non-erosive bottom currents. It is draped by the upper Sigerslev Member, which was laid down in deeper water than any other chalk known from onshore Denmark. Deposition took place under quiet conditions, apparently not influenced by bottom currents. The sparse level-bottom community lived on a seafloor with low nutrient supply. It was characterized by recumbent brachiopods and bivalves, sponges and some spatulate, long-spined echinoids, which were able to traverse the soft substrate. The top part of the Maastrichtian assigned to the Højerup Member, consists of low biogenic chalk mounds formed mainly by profuse growth of small-sized bryozoans governed by nutrient-rich currents from the south. The macrofauna of this member is of very high density and richness, yet species composition is similar to that of the mound-bedded lower Sigerslev Member. The bryozoan thickets of the two members are accompanied by a rich fauna of bivalves, echinoids, polychaetes, gastropods and brachiopods. Attached forms were dependent on hard, mainly small substrates provided largely by dead bryozoans, and on a steady nutrient supply. The bivalve fauna is richer and occurs in slightly higher densities in the Højerup Member than in the similarly mound-bedded lower Sigerslev Member. The number of polychaete species is also greater in the Højerup Member. The faunal differences reflect the shallower-water setting and a higher influx of food during deposition of the latter unit. The final Maastrichtian benthic macrofossil community at Stevns Klint represented by the Højerup Member thus shows the greatest faunal richness and density in the Upper Cretaceous chalk in the Danish Basin. There is no evidence of faunal impoverishment at the end of the Cretaceous in the Stevns Klint succession, which is complete across the Cretaceous–Paleogene boundary, and the study thereby corroborates the increasingly dominant view of a very abrupt faunal turnover at the K/Pg boundary.

Earth Worm Trace Fossils Just After the KT/K-Pg Boundary

Fossil Worm Burrows Reveal Very Early Terrestrial Animal Activity and Shed Light on Trophic Resources after the End-Cretaceous Mass Extinction

Authors:

1. Karen Chin (a)
2. Dean Pearson (b)
3. A. A. Ekdale (c)

Affiliations:

a. Department of Geological Sciences and Museum of Natural History, University of Colorado Boulder, Boulder, Colorado, United States of America

b. Pioneer Trails Regional Museum, Paleontology Department, Bowman, North Dakota, United States of America

c. Department of Geology and Geophysics, University of Utah, Salt Lake City, Utah, United States of America

Abstract:

The widespread mass extinctions at the end of the Cretaceous caused world-wide disruption of ecosystems, and faunal responses to the one-two punch of severe environmental perturbation and ecosystem collapse are still unclear. Here we report the discovery of in situ terrestrial fossil burrows from just above the impact-defined Cretaceous-Paleogene (K/Pg) boundary in southwestern North Dakota. The crisscrossing networks of horizontal burrows occur at the interface of a lignitic coal and silty sandstone, and reveal intense faunal activity within centimeters of the boundary clay. Estimated rates of sedimentation and coal formation suggest that the burrows were made less than ten thousand years after the end-Cretaceous impact. The burrow characteristics are most consistent with burrows of extant earthworms. Moreover, the burrowing and detritivorous habits of these annelids fit models that predict the trophic and sheltering lifestyles of terrestrial animals that survived the K/Pg extinction event. In turn, such detritus-eaters would have played a critical role in supporting secondary consumers. Thus, some of the carnivorous vertebrates that radiated after the K/Pg extinction may owe their evolutionary success to thriving populations of earthworms.

Is Mercury a Signal for Mass Vulcanism Across the KT/K=Pg Boundary?

Mercury as a proxy for volcanic activity during extreme environmental turnover: The Cretaceous-Paleogene transition

Authors:

1. A.N. Sial (a)
2. L.D. Lacerda (b)
3. V.P. Ferreira (a)
4. R. Frei (c)
5. R.A. Marquillas (d)
6. J.A. Barbosa (e)
7. C. Gaucher (f)
8, C.C. Windmöller (g)
9, N.S. Pereira (a)

Affiliations:

a. NEG-LABISE, Department of Geology, Federal University of Pernambuco, Recife, PE, 50740-530, Brazil

b. LABOMAR, Institute of Marine Sciences, Federal University of Ceará, Fortaleza, 60165-081, Brazil

c. Institute of Geography and Geology, University of Copenhagen, Oster Volgade 10, Copenhagen, Denmark, 1350

d. Universidad de Salta, Salta, Argentina CONICET, Buenos Aires 177, 4400 Salta, Argentina

e. LAGESE, Department Geology, Federal University of Pernambuco, Recife, 50740-530, Brazil

f. Facultad de Ciencias, Universidad de La Republica, Montevideo, Uruguay

g. Department of Chemistry, Federal University of Minas Gerais, Av. Antônio Carlos 6627, Belo Horizonte, Minas Gerais, 31270-901, Brazil

Abstract:

The usually low geological background concentrations of Hg makes this trace element suitable for identifying accumulation pulses in sediments that can be tentatively related to weathering processes and thus to climatic changes. Intense volcanism has witnessed the Cretaceous‒Paleogene transition (KTB) and was, perhaps, responsible for dramatic climatic changes and decrease in biodiversity and mass extinction. We have used Hg concentrations as a proxy for volcanic activity and atmospheric Hg and CO2 buildup across the KTB at three localities. In the Salta Basin, Argentina, Hg contents display several spikes across the KTB, with a maximum value of 250 ng.g− 1. In three drill cores across the KTB in the Paraíba Basin, northeastern Brazil, Hg contents increase from the late Maastrichtian to early Danian and Hg spikes predate the KTB, perhaps, as a record of volcanic activity before (but very close to) this transition. At Stevns Klint, Denmark, Hg contents reached almost 250 ng.g− 1 within a 5 cm thick-clay layer, the Fiskeler Member (‘Fish Clay’) that comprises the KTB. Some co-variation between Hg and Al2O3 contents has been observed in all of the studied sections across the KTB, suggesting that Hg is probably adsorbed onto clays. Thermo-desorption experiments in selected samples from the Yacoraite Formation showed Hg+ 2 as the major species present, which is in agreement with a volcanic origin. Combined Hg and C-isotope chemostratigraphy may become a powerful tool for the eventual assessment of the role of volcanic activity during extreme climatic and biotic events, such as those during the KTB.

Mammals Through the KT Extinction

Mammals across the K/Pg boundary in northeastern Montana, U.S.A.: dental morphology and body-size patterns reveal extinction selectivity and immigrant-fueled ecospace filling

Author:

1. Gregory P. Wilson (a)

Affiliations:

a. Department of Biology and Burke Museum of Natural History and Culture, 24 Kincaid Hall, University of Washington, Seattle, Washington 98195-1800 U.S.A.

Abstract:

The Cretaceous/Tertiary (K/Pg) mass extinction has long been viewed as a pivotal event in mammalian evolutionary history, in which the extinction of non-avian dinosaurs allowed mammals to rapidly expand from small-bodied, generalized insectivores to a wide array of body sizes and ecological specializations. Many studies have used global- or continental-scale taxonomic databases to analyze this event on coarse temporal scales, but few studies have documented morphological diversity of mammalian paleocommunities on fine spatiotemporal scales in order to examine ecomorphological selectivity and ecospace filling across this critical transition. Focusing on well-sampled and temporally well-constrained mammalian faunas across the K/Pg boundary in northeastern Montana, I quantified dental-shape disparity and morphospace occupancy via landmark- and semilandmark-based geometric morphometrics and mean body size, body-size disparity, and body-size structure via body-mass estimates.

My results reveal several key findings: (1) latest Cretaceous mammals, particularly metatherians and multituberculates, had a greater ecomorphological diversity than is generally appreciated, occupying regions of the morphospace that are interpreted as strict carnivory, plant-dominated omnivory, and herbivory; (2) the decline in dental-shape disparity and body-size disparity across the K/Pg boundary shows a pattern of constructive extinction selectivity against larger-bodied dietary specialists, particularly strict carnivores and taxa with plant-based diets, that suggests the kill mechanism was related to depressed primary productivity rather than a globally instantaneous event; (3) the ecomorphological recovery in the earliest Paleocene was fueled by immigrants, namely three multituberculate families (taeniolabidids, microcosmodontids, eucosmodontids) and to a lesser extent archaic ungulates; and (4) despite immediate increases in the taxonomic richness of eutherians, their much-celebrated post-K/Pg ecomorphological expansion had a slower start than is generally perceived and most likely only began 400,000 to 1 million years after the extinction event.

Tales from the KT Boundary: Dead Clades Walking?

Survival, but…! New Tales of ‘Dead Clade Walking’ from Austral and Boreal Post-K–T Assemblages

1. J Stillwell (a,*)
2. E Håkansson


a. Applied Palaeontology and Basin Studies Group, School of Geosciences, Monash University, Clayton, Vic 3800, Australia Centre for Evolutionary


*. Author to contact: Jeffrey.Stilwell@sci.monash.edu.au

Abstract:

Our knowledge of postmass extinction biotic trajectories is at the mercy of available data and detailed research on the governing factors of differential extinction/survivorship patterns of fossil biotas. Some taxa managed—barely—to survive major extinction events, but only for the short-term, becoming extinct at variable times in the following geologic stage, having succumbed to myriad natural forces generated by severe paleoenvironmental perturbations. These ‘Dead Clade Walking’ (DCW) organisms should be included in investigations on the resultant effects of the extinction bottleneck and subsequent rebound phase(s). Significantly, even though the ‘big five’ mass extinctions of the Phanerozoic are distinguished primarily by their overwhelming intensities, their magnitudes—and thus importance for shaping the present-day biosphere—have been systematically underestimated, when time frames including immediate, post-apocalyptic DCW taxa are included in survivorship/extinction analyses. Our research from recent studies of Austral and Boreal invertebrates and vertebrates in relation to the Cretaceous–Tertiary (K–T) boundary provides alluring new evidence of the DCW phenomenon, including the short-term survivorship of ammonoid cephalopods and possible non-avian dinosaurs into the dawn of the Cenozoic.

Link. Cenozoic dinosaurs live on.