Eutherian Mammals (Placentals) Evolved Faster Right After Dinosaurs Went Extinct

Eutherians experienced elevated evolutionary rates in the immediate aftermath of the Cretaceous–Palaeogene mass extinction

Authors:

Halliday et al

Abstract:

The effect of the Cretaceous–Palaeogene (K–Pg) mass extinction on the evolution of many groups, including placental mammals, has been hotly debated. The fossil record suggests a sudden adaptive radiation of placentals immediately after the event, but several recent quantitative analyses have reconstructed no significant increase in either clade origination rates or rates of character evolution in the Palaeocene. Here we use stochastic methods to date a recent phylogenetic analysis of Cretaceous and Palaeocene mammals and show that Placentalia likely originated in the Late Cretaceous, but that most intraordinal diversification occurred during the earliest Palaeocene. This analysis reconstructs fewer than 10 placental mammal lineages crossing the K–Pg boundary. Moreover, we show that rates of morphological evolution in the 5 Myr interval immediately after the K–Pg mass extinction are three times higher than background rates during the Cretaceous. These results suggest that the K–Pg mass extinction had a marked impact on placental mammal diversification, supporting the view that an evolutionary radiation occurred as placental lineages invaded new ecological niches during the Early Palaeocene.

pop sci link.

Chicxulub's Impact Caused "Nuclear" Winter in New Jersey

Evidence for Cretaceous-Paleogene boundary bolide "impact winter" conditions from New Jersey, USA

Authors:

Vellekoop et al

Abstract:

Abrupt and short-lived "impact winter" conditions have commonly been implicated as the main mechanism leading to the mass extinction at the Cretaceous-Paleogene (K-Pg) boundary (ca. 66 Ma), marking the end of the reign of the non-avian dinosaurs. However, so far only limited evidence has been available for such a climatic perturbation. Here we perform high-resolution TEX86 organic paleothermometry on three shallow cores from the New Jersey paleoshelf, (northeastern USA) to assess the impact-provoked climatic perturbations immediately following the K-Pg impact and to place these short-term events in the context of long-term climate evolution. We provide evidence of impact-provoked, severe climatic cooling immediately following the K-Pg impact. This so-called "impact winter" occurred superimposed on a long-term cooling trend that followed a warm phase in the latest Cretaceous.

90% of North American Mammals Estimated to Have Died out Because of the Dinosaur Killer

Over 90 per cent of mammal species were wiped out by the same asteroid that killed the dinosaurs in the Cretaceous period 66 million years ago, significantly more than previously thought.

A study by researchers at the Milner Centre for Evolution at the University of Bath and published in the Journal of Evolutionary Biology, reviewed all mammal species known from the end of the Cretaceous period in North America. Their results showed that over 93 per cent became extinct across the Cretaceous-Paleogene (K-Pg) boundary, but that they also recovered far more quickly than previously thought.

The scientists analysed the published fossil record from western North America from two million years before the Cretaceous-Paleogene boundary, until 300,000 years after the asteroid hit. They compared species diversity before and after this extinction event to estimate the severity of the event and how quickly the mammals recovered. The extinction rates were much higher than previous estimates based on more limited data sets.

Dr Nick Longrich from the Milner Centre for Evolution, in the University of Bath's Department for Biology & Biochemistry, explained: "The species that are most vulnerable to extinction are the rare ones, and because they are rare, their fossils are less likely to be found. The species that tend to survive are more common, so we tend to find them.

link.

The Antarctic was NOT a Refuge From the KT/K-Pg Mass Extinction

A study of more than 6,000 marine fossils from the Antarctic shows that the mass extinction event that killed the dinosaurs was sudden and just as deadly to life in the polar regions.

Previously, scientists had thought that creatures living in the southernmost regions of the planet would have been in a less perilous position during the mass extinction event than those elsewhere on Earth.

The research, published today in the journal Nature Communications, involved a six-year process of identifying more than 6,000 marine fossils ranging in age from 69- to 65-million-years-old that were excavated by scientists from the University of Leeds and the British Antarctic Survey on Seymour Island in the Antarctic Peninsula.

link.

Were Dinosaurs in Delcine BEFORE the Chicxulub Impact? Or has Statisticosaurus bit the Paleontologist Again?

Dinosaurs in decline tens of millions of years before their final extinction

Authors:

Sakamoto et al

Abstract:

Whether dinosaurs were in a long-term decline or whether they were reigning strong right up to their final disappearance at the Cretaceous–Paleogene (K-Pg) mass extinction event 66 Mya has been debated for decades with no clear resolution. The dispute has continued unresolved because of a lack of statistical rigor and appropriate evolutionary framework. Here, for the first time to our knowledge, we apply a Bayesian phylogenetic approach to model the evolutionary dynamics of speciation and extinction through time in Mesozoic dinosaurs, properly taking account of previously ignored statistical violations. We find overwhelming support for a long-term decline across all dinosaurs and within all three dinosaurian subclades (Ornithischia, Sauropodomorpha, and Theropoda), where speciation rate slowed down through time and was ultimately exceeded by extinction rate tens of millions of years before the K-Pg boundary. The only exceptions to this general pattern are the morphologically specialized herbivores, the Hadrosauriformes and Ceratopsidae, which show rapid species proliferations throughout the Late Cretaceous instead. Our results highlight that, despite some heterogeneity in speciation dynamics, dinosaurs showed a marked reduction in their ability to replace extinct species with new ones, making them vulnerable to extinction and unable to respond quickly to and recover from the final catastrophic event.

Did Seed Eating Save the Birds at the Cretaceous Paleogene Extinction?

When the dinosaurs became extinct, plenty of small bird-like dinosaurs disappeared along with giants like Tyrannosaurus and Triceratops. Why only some of them survived to become modern-day birds remains a mystery. Now, researchers reporting April 21 in Current Biology suggest that abrupt ecological changes following a meteor impact may have been more detrimental to carnivorous bird-like dinosaurs, and early modern birds with toothless beaks were able to survive on seeds when other food sources declined.

"The small bird-like dinosaurs in the Cretaceous, the maniraptoran dinosaurs, are not a well-understood group," says first author Derek Larson, a paleontologist at the Philip J. Currie Dinosaur Museum in Alberta and PhD candidate at the University of Toronto. "They're some of the closest relatives to modern birds, and at the end of the Cretaceous, many went extinct, including the toothed birds—but modern crown-group birds managed to survive the extinction. The question is, why did that difference occur when these groups were so similar?"

The team of researchers, which also included David Evans of the Royal Ontario Museum and the University of Toronto and Caleb Brown of the Royal Tyrrell Museum of Paleontology, began by investigating whether the extinction at the end of the Cretaceous was an abrupt event or a progressive decline simply capped off by the meteor impact. The fossil record holds evidence to support both scenarios, depending on which dinosaurs are being examined.

Delving into the bird-like dinosaurs, Larson collected data describing 3,104 fossilized teeth from four different maniraptoran families. Some were already published, but much of the information came from Larson's own work at the microscope, cataloging the shape and size of each tooth.

link.

Chicxulub Impact, not Deccan Traps, Killed Dinosaurs Based on Ocean Chemistry Evidence

Biogeochemical significance of pelagic ecosystem function: an end-Cretaceous case study

Authors:

Henehan et al

Abstract:

Pelagic ecosystem function is integral to global biogeochemical cycling, and plays a major role in modulating atmospheric CO2 concentrations (pCO2). Uncertainty as to the effects of human activities on marine ecosystem function hinders projection of future atmospheric pCO2. To this end, events in the geological past can provide informative case studies in the response of ecosystem function to environmental and ecological changes. Around the Cretaceous–Palaeogene (K–Pg) boundary, two such events occurred: Deccan large igneous province (LIP) eruptions and massive bolide impact at the Yucatan Peninsula. Both perturbed the environment, but only the impact coincided with marine mass extinction. As such, we use these events to directly contrast the response of marine biogeochemical cycling to environmental perturbation with and without changes in global species richness. We measure this biogeochemical response using records of deep-sea carbonate preservation. We find that Late Cretaceous Deccan volcanism prompted transient deep-sea carbonate dissolution of a larger magnitude and timescale than predicted by geochemical models. Even so, the effect of volcanism on carbonate preservation was slight compared with bolide impact. Empirical records and geochemical models support a pronounced increase in carbonate saturation state for more than 500 000 years following the mass extinction of pelagic carbonate producers at the K–Pg boundary. These examples highlight the importance of pelagic ecosystems in moderating climate and ocean chemistry.

The Ability to Enter Torpor Might Have Saved Mammals Across the KT/K-Pg Mass Extinction

Cool echidnas survive the fire

Authors:

Nowack et al

Abstract:

Fires have occurred throughout history, including those associated with the meteoroid impact at the Cretaceous–Palaeogene (K–Pg) boundary that eliminated many vertebrate species. To evaluate the recent hypothesis that the survival of the K–Pg fires by ancestral mammals was dependent on their ability to use energy-conserving torpor, we studied body temperature fluctuations and activity of an egg-laying mammal, the echidna (Tachyglossus aculeatus), often considered to be a ‘living fossil’, before, during and after a prescribed burn. All but one study animal survived the fire in the prescribed burn area and echidnas remained inactive during the day(s) following the fire and substantially reduced body temperature during bouts of torpor. For weeks after the fire, all individuals remained in their original territories and compensated for changes in their habitat with a decrease in mean body temperature and activity. Our data suggest that heterothermy enables mammals to outlast the conditions during and after a fire by reducing energy expenditure, permitting periods of extended inactivity. Therefore, torpor facilitates survival in a fire-scorched landscape and consequently may have been of functional significance for mammalian survival at the K–Pg boundary.

A Contrarian K-Pg/KT Mass Extinction Root Cause Proposal

End-cretaceous cooling and mass extinction driven by a dark cloud encounter

Authors:

Nimura et al

Abstract:

We have identified iridium in an ~5 m-thick section of pelagic sediment cored in the deep sea floor at Site 886C, in addition to a distinct spike in iridium at the K-Pg boundary related to the Chicxulub asteroid impact. We distinguish the contribution of the extraterrestrial matter in the sediments from those of the terrestrial matter through a Co-Ir diagram, calling it the "extraterrestrial index" fEX. This new index reveals a broad iridium anomaly around the Chicxulub spike. Any mixtures of materials on the surface of the Earth cannot explain the broad iridium component. On the other hand, we find that an encounter of the solar system with a giant molecular cloud can aptly explain the component, especially if the molecular cloud has a size of ~100 pc and the central density of over 2000 protons/cm^3. Kataoka et al. (2013, 2014) pointed that an encounter with a dark cloud would drive an environmental catastrophe leading to mass extinction. Solid particles from the hypothesized dark cloud would combine with the global environment of Earth, remaining in the stratosphere for at least several months or years. With a sunshield effect estimated to be as large as -9.3 W m^-2, the dark cloud would have caused global climate cooling in the last 8 Myr of the Cretaceous period, consistent with the variations of stable isotope ratios in oxygen (Barrera and Huber, 1990; Li and Keller, 1998; Barrera and Savin, 1999; Li and Keller, 1999) and strontium (Barrera and Huber, 1990; Ingram, 1995; Sugarman et al., 1995). The resulting growth of the continental ice sheet also resulted in a regression of the sea level. The global cooling, which appears to be associated with a decrease in the diversity of fossils, eventually led to the mass extinction at the K-Pg boundary.

Colombian Island has 2 cm Spherulites From the Chicxulub Impact that Wiped out the Dinosaurs

A team of scientists working on the Colombian island of Gorgonilla, in the Pacific, has found fragments of the meteorite that 66 million years ago caused the extinction of the dinosaurs, sources close to the investigation said Tuesday.

“(We have) evidence of the impact of the meteorite, (they are very tiny) particles that are the result when the meteorite hit,” geologist Herman Bermudez told Spanish news agency EFE.

Those remains, called spherulites, which are small, rounded bodies that commonly occur in vitreous igneous rocks, are part of the continental shelf material that is currently the Yucatan Peninsula and they were found with fragments of the meteorite.

The spherulites are 2 cm (about 0.8 inches) in diameter and look like marbles, being made of glass.

Under the microscope small crystals from the meteorite can be seen and they show its composition.

When the meteorite hit Earth, it blasted out a crater 200 km (125 mi.) in diameter known today as Chicxulub, which is on the Yucatan Peninsula.

link.

The End of All Things #3

Cretaceous-Paleogene (K-Pg/KT) Mass Extinction:

The Chicxulub Impact Crater will be drilled. Some are saying for the first time, but I do believe the original oil workers who reported it back in the 80s (?) did so before.

There was a partial collapse of the marine carbon pump at the K-Pg boundary.marine

Permian Triassic Mass Extinction:

There is contrary evidence from conondont tooth oxygen isotopes suggesting a sharp temperature drop right at the PT Extinction. This is contrary to the global cooking scenario.

The Permian ocean bottom waters in China were not anoxic at the time of the PT Extinction.

In South China, the redox conditions were fluctuating at the PT Boundary.

The Kayitou Formation in China appears to have the terrestrial record of the PT Extinction.

There is also evidence of cyanobacteria blooms from China as well across the PT.

Devonian Mass Extinctions:

Here's evidence of what happened during the Famenian-Frasnian Event (aka mass extinction) in Devonian in China.

There was a disruption in the nitrogen cycle at the end Devonian Mass Extinction.

Here's some more interesting evidence of what was going on during the end Devonian Mass Extinction.

End of all Things #1: a Mass Extinction Aggregation Post

Ediacaran/Cambrian Extinction:

Were the Ediacaran's wiped out, in part and the Cambrian Explosion initiated by greatly increased UV radiation?

Permian Triassic Mass Extinction:

The Permian Triassic boundary has been geochronologically located in the Spanish Pyrenees and produced an interesting and diverse fauna from the early Triassic.

The early Triassic locales of the Persian Gulf show evidence of repeated and sustained conditions like during the mass extinction itself.

Cretaceous-Paleogene (KT) Mass Extinction:

Another extraordinary claim that the KT/K-Pg mass extinction was caused by dark matter has been made.

Sixth Mass Extinction:

The carbon dates in North America appear to match well with the Human Overkill Hypothesis for the reason why the megafauna (mammoths, sloths, dire wolves, etc) went extinct.

What were the implications of the loss of large Pleistocene carnivores on the ecosystem?

Or for that matter for the impact of the loss of ALL the missing megafauna on the ecosystem?  Or more specifically on the forests?  Was the impact uniform or variable on the ecosystems of North and South America?

What were the changes on the nutrient cycle with the extinctions taking place?

Or!  Gasp!  The lack of mammoths farts on the atmosphere?

Or in the sea coast, what about the impacts of the extinction of the stellar's sea cow?

The data strongly supports the extinction of Australia's giant bird, Genyornis, as being caused by humans.

In fact, multiple sources of data suggest humanity was the cause of the extinctions in the Sahul (greater Australia).

META:

The proposed planet 9, proposed by Caltech astronomers, is unlikely to have anything to do with the mass extinctions on Earth.  Even so, if it pans out, for historical reasons, I hope they name the new planet 'Nemesis.'

Placental Mammals Exploded in Diversity After the KT/K-Pg Mass Extinction

Resolving the relationships of Paleocene placental mammals

Authors:

Halliday et al

Abstract:

The ‘Age of Mammals’ began in the Paleocene epoch, the 10 million year interval immediately following the Cretaceous–Palaeogene mass extinction. The apparently rapid shift in mammalian ecomorphs from small, largely insectivorous forms to many small-to-large-bodied, diverse taxa has driven a hypothesis that the end-Cretaceous heralded an adaptive radiation in placental mammal evolution. However, the affinities of most Paleocene mammals have remained unresolved, despite significant advances in understanding the relationships of the extant orders, hindering efforts to reconstruct robustly the origin and early evolution of placental mammals. Here we present the largest cladistic analysis of Paleocene placentals to date, from a data matrix including 177 taxa (130 of which are Palaeogene) and 680 morphological characters. We improve the resolution of the relationships of several enigmatic Paleocene clades, including families of ‘condylarths’. Protungulatum is resolved as a stem eutherian, meaning that no crown-placental mammal unambiguously pre-dates the Cretaceous–Palaeogene boundary. Our results support an Atlantogenata–Boreoeutheria split at the root of crown Placentalia, the presence of phenacodontids as closest relatives of Perissodactyla, the validity of Euungulata, and the placement of Arctocyonidae close to Carnivora. Periptychidae and Pantodonta are resolved as sister taxa, Leptictida and Cimolestidae are found to be stem eutherians, and Hyopsodontidae is highly polyphyletic. The inclusion of Paleocene taxa in a placental phylogeny alters interpretations of relationships and key events in mammalian evolutionary history. Paleocene mammals are an essential source of data for understanding fully the biotic dynamics associated with the end-Cretaceous mass extinction. The relationships presented here mark a critical first step towards accurate reconstruction of this important interval in the evolution of the modern fauna.

~13% of Calcareous Nannoplankton Survived the K-Pg/K-T Mass Extinction

Calcareous nannoplankton assemblage changes linked to paleoenvironmental deterioration and recovery across the Cretaceous–Paleogene boundary in the Betic Cordillera (Agost, Spain)

Authors:

Lamolda et al

Abstract:

Investigations of calcareous nannoplankton assemblages including species richness and abundance data were performed across the K–Pg boundary interval at Agost (SE Spain), between − 100 cm and + 100 cm, below and, respectively, above the boundary, at a considerable high resolution averaging 2 cm. From a total of 98 species of the Upper Maastrichtian, only 13 survived mass extinction, while the rest of the 86% vanished in the K–Pg fallout layer. A slight progressive decline in species richness and abundance was observed toward the top of the Maastrichtian, where mixed assemblages, consisting of both cold-water taxa and typical Tethyan ones are present. Four successive acme events were observed, i.e. Markalius inversus and the calcareous dinoflagellate genus Thoracosphaera starting from the base of the Paleocene, followed by those of Braarudosphaera bigelowii and Neobiscutum parvulum. The most prominent acme intervals belong to Thoracosphaera spp. and B. bigelowii, opportunistic taxa, for which the survival strategy may be linked to their capability to encyst and survive severe environmental deterioration. At the upper part of the studied succession, calcareous nannoplankton assemblages are already dominated by survivor species, as well as incoming ones, showing an early pioneer calcareous nannoplankton ecosystems about 35–40 kyr after the K–Pg boundary. Correlation between the calcareous nannoplankton assemblage fluctuation, including species richness and abundance, and the paleoenvironmental changes, such as the eustatic and climatic modifications, are also discussed.

Sea Grass Meadow and Foraminifera Relationship may Predate the Cretaceous-Paleogene Mass Extinction

The Cretaceous/Paleogene boundary: Foraminifera, sea grasses, sea level change and sequence stratigraphy

Authors:

Hart et al

Abstract:

The tsunami generated by the Chicxulub impact eroded the uppermost Cretaceous surface of the Gulf Coast region (U.S.A.) forming a distinctive topography that was previously interpreted as a sequence boundary. At more distal sites, such as Stevns Klint (Denmark), there appears to be no sequence boundary at the Cretaceous/Paleogene boundary but there is one within the uppermost Maastrichtian, between the Sigerslev and Højerup members, and another in the lowermost Paleocene (top of Zone P1a). Both of these surfaces are identified by distinctive, phosphatized, and incipient hardgrounds. The changes in sea level involved in the generation of uppermost Cretaceous sequences are thought to have been minimal as, in the Gulpen and Maastricht formations of the Maastricht area (Netherlands), the presence of sea grasses and their associated foraminifera would indicate that the chalk sea floor remained within the range of water depth that would allow photosynthesis (less than 20 m), even across the postulated sequence boundaries. The assemblages of foraminifera associated with sea grasses in the uppermost Maastrichtian are comparable in morphology with those associated with modern sea grass meadows and indicate a relationship that may have existed since, at least, the latest Cretaceous.

Did the Chicxulub Impact Trigger a Massive, Global Algae Bloom?

NOx production and rainout from Chicxulub impact ejecta reentry

Authors:

Parkos et al

Abstract:

The Chicxulub impact 66.0 Ma ago initiated the second biggest extinction in the Phanerozoic Eon. The cause of the concurrent oceanic nitrogen isotopic anomaly, however, remains elusive. The Chicxulub impactor struck the Yucatán peninsula, ejecting 2 × 1015 kg of molten and vaporized rock that reentered globally as approximately 1023 microscopic spherules. Here we report that modern techniques indicate that this ejecta generates 1.5 × 1014 moles of NOx, which is enough to cause the observed nitrogen enrichment of the basal layer. Additionally, reentry-based NO production would explain the anomalously heavy isotopic composition of the observed nitrogen. We include N, O, N2, O2, and NO species in simulations of nonequilibrium chemically reacting flow around a reentering spherule. We then determine the net production of NO from all the spherules and use turbulence models to determine how quickly this yield diffuses through the atmosphere. Upon reaching the stratosphere and troposphere, cloud moisture absorbs the NOx and forms nitric acid. We model this process and determine the acidity of the resulting precipitation, which peaks about 1 year after the impact. The precipitation ultimately reaches the upper ocean, where we assume that the well-mixed surface layer is 100 m deep. We then model the naturally occurring carbonate/bicarbonate buffer and determine the net pH. We find that insufficient NOx reaches the ocean to directly cause the observed end-Cretaceous oceanic extinction via acidification and buffer removal. However, the resulting nitrates are sufficient to explain the concurrent nitrogen isotopic anomaly and facilitate an end-Cretaceous algae bloom.

Did Modern Birds Evolve in Turonian/Coniacian Cretaceous South America and Spread Worldwide After K-Pg/K-T Mass Extinction

New research led by the American Museum of Natural History reveals that the evolution of modern birds was greatly shaped by the history of our planet's geography and climate. The DNA-based work, published today in the journal Science Advances, finds that birds arose in what is now South America around 90 million years ago, and radiated extensively around the time of the Cretaceous-Paleogene extinction event that killed off the non-avian dinosaurs. The new research suggests that birds in South America survived this event and then started moving to other parts of the world via multiple land bridges while diversifying during periods of global cooling.

"Modern birds are the most diverse group of terrestrial vertebrates in terms of species richness and global distribution, but we still don't fully understand their large-scale evolutionary history," said Joel Cracraft, a curator in the Museum's Department of Ornithology and co-author of the paper. "It's a difficult problem to solve because we have very large gaps in the fossil record. This is the first quantitative analysis estimating where birds might have arisen, based on the best phylogenetic hypothesis that we have today."

Cracraft and lead author Santiago Claramunt, a research associate in the Museum's Department of Ornithology, analyzed DNA sequences for most modern bird families with information from 130 fossil birds to generate a new evolutionary time tree.

link.

Dr Gerta Keller Trumpets a Charge: Multiple Papers About Deccan Traps and the the K-Pg/KT Mass Extinction

Dr Keller has been leading an insurgency against the idea the Chicxulub impact was the underlying event that brought about the Cretaceous-Paleogene (K-Pg) Mass Extinction (formerly the KT Extinction).  This is rather contrarian to the generally accepted theory.  

The journal Paleaeogeography, Palaeoclimateology, Palaeoecology has an issue dedicated to how volcanic eruptions impacted (see what I did there?) past mass extinctions (or didn't as it may be).  That's the reason for all the volcano related posts this past week.  

Dr Keller's 'team' has a large number of articles in the publication.  Rather than do my traditional one-paper-per-post method, I am going to do a list here of each.  The reason being I don't buy her hypothesis that the Deccan Traps caused the mass extinction during the Maastrichtian.  I've posted as much since the evidence comparing mass extinctions already strongly tied to volcanic eruptions is rather different from what is present for the K-Pg Extinction.  I wrote as much in the Stop Dreaming post.  

That said, I am sure the Deccan Traps did cause some environmental impacts (see!), but they are insufficient to have caused the mass extinction.

While I admire tenacity, I think she has crossed over to religion.  However, rather than ignoring the recent papers, since they are peer reviewed papers in a respected journal, I am going to link to each here with a very short title and a description of each and a short comment.

Upheavals during the Late Maastrichtian: Volcanism, climate and faunal events preceding the end-Cretaceous mass extinction. Keller et al present their case the Maastrichtian Cretaceous was a time a climate upheaval and ecological degradation caused by the Deccan Traps with the ecology dominated by opportunistic, disaster taxa.  My comment: T rex.  Too big.

A multi-proxy approach to decode the end-Cretaceous mass extinction. Punekar argues there are multiple bits of evidence suggest the Deccan Traps caused the mass extinction at the K-Pg, especially the release of 12 to 28 teratons of carbon. Comment: Unfortunately, in the same journal edition, the OAE1 from the Early Aptian Cretaceous is stated to have been caused by the release of 20 teratons of carbon. The OAE1 was a mass extinction but a very, very mild one. Additionally, in a surprise result, calciferous plankton actually grow MORE with higher carbon dioxide levels, not less as was expected.

Tracing acidification induced by Deccan Phase 2 volcanism. Font et al ID some potential evidence of aquatic acidification at the end of the Deccan 2 Eruptions. These are located in India. Comment: Best to check to see how global this was before making a claim of global occurrence.

Palaeoenvironmental changes associated with Deccan volcanism, examples from terrestrial deposits from Central India. Fantasia et al present evidence of local impacts of the Deccan Traps caused stressed environment from India. Their claim is the DT caused environmental stress and could have made the Maastrichtian fauna vulnerable to a mass extinction at the end of the Cretaceous. Comment: Possible, but this could be completely local. Mount ST Helens did enormous damage locally, but only modestly globally.

Climatic fluctuations and sea-surface water circulation patterns at the end of the Cretaceous era: Calcareous nannofossil evidence. Thibault et al make the argument surface plankton became stressed and lost species during the proposed Deccan Warmings. However, 100k to 140k years before the K-Pg Boundary, the plankton had regained their species richness. Comment: Interesting. Given the problems of IDing what forminifers are what species I'd be cautious. The recovery would suggest whatever stress caused by the DTs had ended though.

The Role of Hell Creek Formation in Understanding the KT/K-Pg Mass Extinction

The Hell Creek Formation and its contribution to the Cretaceous–Paleogene extinction: A short primer

Authors:

Fastovsky et al

Abstract:

Although it represents but one geographic data point, the uppermost Maastrichtian Hell Creek Formation (HCF), exposed in the upper Great Plains of the North American craton, remains the most studied source for understanding the final ∼1.5 Myr of the Mesozoic Era in the terrestrial realm. Because it lies conformably below the earliest Paleocene Fort Union Formation, and together these two units preserve a rich fauna and flora, much of what is understood about the terrestrial Cretaceous–Paleogene (K–Pg) boundary comes from this sequence.

The HCF has been reconstructed as an expansive, fluvially drained, low coastal plain, built out, to the west, against the Laramide Orogen, and to the east, against the ultimate transgression (Cannonball) of the Western Interior Sea. Its meandering rivers and moist soils supported a multi-tiered angiosperm-dominated flora and rich insect and vertebrate faunas, including dinosaurs, crocodilians, squamates, turtles, and mammals. A dramatic facies change representing the initiation of catastrophic flooding is preserved, within available levels precision, at the K–Pg boundary.

High-precision stratigraphy has proven difficult in this lenticular fluvial system. Where present, the boundary can be recognized by the bipartite boundary claystone; otherwise, palynostratigraphy has proven a powerful tool. Numerical dates have been successfully obtained from in tonsteins at the boundary and above, in the Fort Union; however, these have proven elusive below the boundary within the HCF. The K–Pg boundary in this region is dated at 66.043 Ma (Renne et al., 2013). Magnetostratigraphic studies have been carried out in the HCF; although all but one have lacked numerical dates, these have been used for correlations of widespread, disjunct exposures and for the estimation of sedimentation rates.

The palynoflora is largely homogenous through the HCF; at the K–Pg boundary, it shows an abrupt ∼30% extinction. This makes it a powerful tool for identification of the K–Pg boundary, although because the boundary is identified on absence of Cretaceous taxa rather than presence of earliest Paleocene taxa, several competing methods have been applied to identifying the K–Pg boundary using pollen.

The macroflora, consisting largely of leaves, consists of three successive floras, showing increasing diversity through the HCF. The ultimate of these three floras undergoes an abrupt 57% extinction; taken as a whole, however, the macroflora undergoes a 78% extinction at the K–Pg boundary.

The best data available for dinosaurs – including archaic Aves – show an abrupt extinction. By contrast, salamanders and other lissamphibians, as well as chelonians, cross the boundary virtually without perturbation. Squamates appear to have suffered significant extinctions at the K–Pg boundary, as did euselachians (elasmobranchs) and insects. Mammals suffered a 75% extinction; however, some of this figure cannot be shown to have occurred in less than the last 500 kyr of the Cretaceous, and thus has been potentially attributable to causes other than a bolide impact. Taken together, the survivorship patterns are concordant with the catastrophic inception of ubiquitous flooding characterizing the K–Pg boundary.

While the key K–Pg boundary question in the HCF was once the rate of the biotic extinction, it has moved to the distinction between single-cause scenarios, with the Chicxulub bolide as agent of extinction, and multi-cause scenarios, uniting habitat partitioning, Deccan flood-basalt volcanism, climate change, competition, and bolide impact. Not every potential environmental perturbation need be a mechanism for the extinction: parsimony and the data continue to be concordant with a bolide impact as the single agent of the terrestrial K–Pg mass extinction.

What Crocodylomorphs Survived the KT/K-Pg Asteroid Impact Extinction in Europe

Review of the Late Cretaceous-early Paleogene crocodylomorphs of Europe: Extinction patterns across the K-PG boundary

Authors:

Puértolas-Pascual et al

Abstract:

Although the European dinosaur succession during the latest Cretaceous and its relationship with the Cretaceous-Paleogene (K-Pg) mass extinction has been the focus of recent work, other continental vertebrates, such as crocodylomorphs, have received less attention. The European continental record of crocodylomorphs in general, and of eusuchians in particular, is relatively dense through the Maastrichtian until the K-Pg boundary. Traditionally it has been argued that continental crocodylomorphs were minimally impacted by the K-Pg extinction, but they were substantially affected in Europe with the disappearance of endemic eusuchians such as Hylaeochampsidae, Allodaposuchus and their close relatives, and non-eusuchians such as Doratodon or Theriosuchus. Despite extensive sampling in Danian continental deposits, only scarce fragmentary crocodylomorph remains have been cited. It is not until the late Paleocene and Eocene that a recovery in continental crocodylomorphs is observed. The presence of taxa such as planocraniids, the alligatoroids Diplocynodon and Hassiacosuchus, and stem crocodyloids during this period provide the first reliable continental records of Crocodylia in Europe and is best explained by post-extinction immigration from Asia or North America. By contrast, marine forms such as Thoracosaurus are found on both sides of the K-Pg boundary in Europe. The adaptation of these marine animals to different environments, from shallow seas to more transitional or fluvial environments, could be the key to their success and survival across the K-Pg boundary, as seen in other marine crocodylomorph clades such as Dyrosauridae.