Cretaceous-Tertiary Boundary Research Articles

ОПРЕДЕЛЕНИЕ ИЗОТОПНОГО ВОЗРАСТА ЦИРКОНА ИЗ ТУФОВ СТРАТОТИПИЧЕСКОГО РАЗРЕЗА ЦАГАЯНСКОЙ СЕРИИ (ПРИАМУРЬЕ, ГРАНИЦА МЕЛА И ПАЛЕОГЕНА)

Any study of the boundaries of stratigraphic units in continental sequences always encounters difficulties. A sample was taken from a stratotype of the Tsagayan formation and a typical locality of the Tsagayan flora in the Amur region from crystalloclastic tuffs at the Cretaceous-Paleogene boundary to study zircon and determine its absolute age. The age of the zircons from tuffs was estimated as 68.6 ± 0.8 Ma by the lower intersection with the concordia and can be considered as close to the rock sedimentation time.

Subsurface geology and geochemical evaluation of the Middle Jurassic-Lower Cretaceous organic-rich intervals, West Kalabsha area, Western Desert, Egypt

The West Kalabsha (WKAL) area is a western extreme exploratory area of the Faghur Basin in the Western Desert of Egypt. The study of four wells (WKAL; A-1 X, K-1 X, P-1X, and C-1 X), interpreted with twenty seismic lines, shows that the area is dissected by a series of normal faults with an irregular, E–W strike direction. The general trend of the throw is toward the south–southeast. The most prospective area for hydrocarbon (HC) migration is toward the north (upthrown side) of an E-W striking normal fault north of the WKAl-K-1 X and A-1 X wells. The WKAL-P-1 X and WKAL-K-1 X wells in the Faghur Basin were selected for both geochemical evaluation of possible source rock intervals and burial history modelling within the basin. Integration of the wire-line logs with geochemical analysis identified six organic matter-rich intervals (OMRIs) within the Middle Jurassic-Lower Cretaceous sequence. Four intervals are in the Alam El-Bueib-3C (AEB-3C) member with a cumulative vertical thickness of 530ft. The other OMRIs are 110ft in thickness recorded within the AEB-6 (10ft) and Upper Safa (100ft) members. The studied organic matter (OM) reveals type III, IIIC, and IV kerogens (mainly gas-prone) with a terrestrial origin. They have reached a maturity level consistent with the late oil window. The expulsion threshold depth detected in the WKAL-P-1 X well is 12000ft in the AEB-3C member, whereas the active source depth limit (ASDL) is 15000ft in the Safa Member. The present study suggests a paleo-geothermal gradient range between 1.13oF/100ft and 1.39oF/100ft with an estimated regional erosion of 5500 to 7000ft of strata mainly between the Paleozoic-Jurassic and Cretaceous-Tertiary boundaries. The present-day geothermal gradient based on bottom-hole temperatures shows a geothermal gradient of 1.4oF/100ft (WKAL-P-1 X), that increases to the north to 1.65oF/100ft (WKAL-K-1 X). Burial history modelling reveals that sedimentary strata entered the mature oil zone in the Early Cretaceous (110–115Ma) at depths of 7500–8000ft in the deepest part of WKAL-P-1 X and WKAL-K-1 X wells (Paleozoic strata). Maturation continued to present, resulting in Jurassic and Lower Cretaceous strata currently falling into the late oil window.

Mercury evidence of Deccan volcanism driving the Latest Maastrichtian warming event

Abstract The timing and ecological impacts of the Deccan Traps large igneous province eruption are vigorously debated. Pre–Cretaceous-Paleogene (KPg) boundary impacts of Deccan volcanism have been widely identified in marine sediments, but direct evidence of terrestrial impacts remains rare. We used mercury concentrations and isotopic compositions, a proxy for volcanic activity, to assess impacts on terrestrial environments. We studied two drill cores across the KPg boundary in eastern China that represent two different depositional environments: clastic deposits in the Jiaolai Basin and carbonate deposits in the Pingyi Basin. Both drill cores exhibit strong Hg enrichment prior to the KPg boundary. Near consistent mass-independent fractionation (MIF) of odd-Hg isotopes (odd-MIF) in the Jiaolai Basin likely indicates a volcanogenic source of Hg spikes below the KPg boundary. Odd-MIF isotopes in the Pingyi Basin likewise suggest a volcanogenic Hg source but with a terrestrial Hg signature of lower Δ199Hg values before and after the Hg spike interval. The Hg enrichment level can be stratigraphically correlated to the beginning of the Latest Maastrichtian warming event (LMWE) and is consistent with a strong, negative carbon-isotope excursion (CIE) in both δ13Corg (organic matter) and δ13Ccarb (carbonate), suggesting a disturbance of the global carbon cycle induced by a major pulse of Deccan Traps volcanism. Our discovery of a ter-restrial record of pre-KPg boundary Deccan volcanism provides robust evidence of global influence of the Deccan Traps large igneous province during the LMWE.

Stratigraphic palynology and micropaleontological study of the Cretaceous-Paleogene succession of the Nani-1 well of the Anambra and Niger Delta basins: Implications for hydrocarbon exploration

Integrated palynological and micropaleontological analyses were carried out on the Nani-1 well drilled into the Anambra and Niger Delta basins of Nigeria. The study is aimed at reconstructing biozones and paleoenvironments of deposition, as well as deducing the sequence stratigraphic framework of the Cretaceous-Paleogene successions of an area containing key elements for hydrocarbon exploration. Encountered lithofacies succession of sandstone, siltstone, dark-grey to black shale, and coal beds comprises six lithostratigraphic units, namely the Nkporo Group (Campanian-Maastrichtian), Mamu Formation (Middle Maastrichtian), Ajali Formation (Middle-Late Maastrichtian), Nsukka Formation (Late Maastrichtian), Imo Formation (Danian-Thanetian) and Ameki Group (Eocene). Fourteen dinoflagellate zones (A-N) and seven pollen and spore subzones (A1-G1) are recognized based on the first occurrence of two or more species. Two major stratigraphic events are documented: (1) dinoflagellate cyst (dinocyst) zone G at 880 m depth marked by first appearance of Danea aff. californica and Danea cf. mutabilis in association with Cordosphaeridium fibrospinosum, and the last occurrence of Danea aff. californica and Phelodinium magnificum place the Cretaceous-Paleogene (K/Pg) boundary in the lowermost part of the Imo Formation; and (2) a hiatus characterized by a starved section observed at 380 m directly overlain by the Early Eocene assemblages of the Ameki Group indicates a sequence boundary at Imo/Ameki Boundary. Thus, a chronostratigraphic chart is developed for parts of the Anambra Basin and the Niger Delta. Six depositional environments which include marginal to shallow marine, marshy lagoon to estuarine, shallow neritic and tidally influenced fluvial channel are identified, and palynostratigraphic evidences indicate that fresh water palynomorphs are present in the Lower Maastrichtian strata. Four sequence boundaries and four maximum flooding surfaces are also identified within the Maastrichtian–Early Eocene sediments. The paleoenvironmental reconstruction shows that possible hydrocarbon reservoirs in the basin are the marine sandstone facies of the Nkporo Group and Mamu Formation. Their shale members constitute potential source rocks, while the overlying shale units of the Nsukka and Imo formations may provide regional seals for hydrocarbon habitation.

Phylogenomic Coalescent Analyses of Avian Retroelements Infer Zero-Length Branches at the Base of Neoaves, Emergent Support for Controversial Clades, and Ancient Introgressive Hybridization in Afroaves.

Retroelement insertions (RIs) are low-homoplasy characters that are ideal data for addressing deep evolutionary radiations, where gene tree reconstruction errors can severely hinder phylogenetic inference with DNA and protein sequence data. Phylogenomic studies of Neoaves, a large clade of birds (>9000 species) that first diversified near the Cretaceous–Paleogene boundary, have yielded an array of robustly supported, contradictory relationships among deep lineages. Here, we reanalyzed a large RI matrix for birds using recently proposed quartet-based coalescent methods that enable inference of large species trees including branch lengths in coalescent units, clade-support, statistical tests for gene flow, and combined analysis with DNA-sequence-based gene trees. Genome-scale coalescent analyses revealed extremely short branches at the base of Neoaves, meager branch support, and limited congruence with previous work at the most challenging nodes. Despite widespread topological conflicts with DNA-sequence-based trees, combined analyses of RIs with thousands of gene trees show emergent support for multiple higher-level clades (Columbea, Passerea, Columbimorphae, Otidimorphae, Phaethoquornithes). RIs express asymmetrical support for deep relationships within the subclade Afroaves that hints at ancient gene flow involving the owl lineage (Strigiformes). Because DNA-sequence data are challenged by gene tree-reconstruction error, analysis of RIs represents one approach for improving gene tree-based methods when divergences are deep, internodes are short, terminal branches are long, and introgressive hybridization further confounds species–tree inference.

An updated suprageneric classification of planktic foraminifera after growing evidence of multiple benthic-planktic transitions

Planktic foraminifera have traditionally been classified within a single order: Globigerinida. However, recent phylogenetic studies, both molecular and stratophenetic, are evidencing the polyphyletic origin of planktic foraminifera from several benthic ancestors. At least four independent events of benthic-planktic transition have been identified. One of them occurred after the Cretaceous–Paleogene boundary mass extinction, originating the first Cenozoic globigerinids. Another three occurred in the Mesozoic, originating three groups of planktic foraminifera (globotruncanids, heterohelicids and guembelitriids) not related phylogenetically to each other or to current globigerinids. These findings make it necessary to carry out an exhaustive review of their suprageneric systematics, mainly at the order level. Here we propose a new, more natural classification, grouping them into four orders: Globigerinida, Heterohelicida, Globotruncanida n. ord., and Guembelitriida n. ord. To better reflect the diversity and phylogeny of planktic foraminifera, we have also defined two new superfamilies: Abathomphaloidea n. superfam. and Parvularugoglobigerinoidea n. superfam., and one new family: Parvularuglobigerinidae n. fam.

No Consistent Shift in Leaf Dry Mass per Area Across the Cretaceous-Paleogene Boundary.

The Chicxulub bolide impact has been linked to a mass extinction of plants at the Cretaceous—Paleogene boundary (KPB; ∼66 Ma), but how this extinction affected plant ecological strategies remains understudied. Previous work in the Williston Basin, North Dakota, indicates that plants pursuing strategies with a slow return-on-investment of nutrients abruptly vanished after the KPB, consistent with a hypothesis of selection against evergreen species during the globally cold and dark impact winter that followed the bolide impact. To test whether this was a widespread pattern we studied 1,303 fossil leaves from KPB-spanning sediments in the Denver Basin, Colorado. We used the relationship between petiole width and leaf mass to estimate leaf dry mass per area (LMA), a leaf functional trait negatively correlated with rate of return-on-investment. We found no evidence for a shift in this leaf-economic trait across the KPB: LMA remained consistent in both its median and overall distribution from approximately 67 to 65 Ma. However, we did find spatio-temporal patterns in LMA, where fossil localities with low LMA occurred more frequently near the western margin of the basin. These western margin localities are proximal to the Colorado Front Range of the Rocky Mountains, where an orographically driven high precipitation regime is thought to have developed during the early Paleocene. Among these western Denver Basin localities, LMA and estimated mean annual precipitation were inversely correlated, a pattern consistent with observations of both fossil and extant plants. In the Denver Basin, local environmental conditions over time appeared to play a larger role in determining viable leaf-economic strategies than any potential global signal associated with the Chicxulub bolide impact.

Geologically constrained astronomical solutions for the Cenozoic era

Astronomical solutions provide insight into the Solar System's dynamical evolution and are indispensable tools in cyclostratigraphy and astrochronology. Constructing an absolute, fully calibrated astronomical time scale (ATS) has hitherto been hindered beyond ∼50 Ma because orbital calculations disagree before that age due to solar system chaos. We have recently developed a new approach that allows extending the fully calibrated astronomical time scale to ∼58 Ma. Here, we present geologic data and new astronomical solutions, extending our approach across the Paleocene epoch (∼66 to ∼56 Ma). New astronomical solutions were generated using numerical solar system integrations following our earlier work, which now provides geologically constrained astronomical solutions for the Cenozoic era (66-0 Ma). The orbital solutions are available to 300 Ma — we caution, however, that the time interval 300-66 Ma is unconstrained due to dynamical chaos in the solar system. We have tested the sensitivity of our new solutions to various parameters, including numerical stepsize, solar quadrupole moment, number of asteroids included, initial positions, and tidal dissipation. We demonstrate that our new solutions yield improved agreement with the geologic record across the Paleocene epoch, compared to previously available astronomical solutions for that period. Furthermore, we discuss implications of our results for solar system chaos and resonance transitions. We have also obtained K/T boundary (KTB) ages based on our new solutions, which suggest slightly younger KTB ages than those inferred from most recent 40Ar/39Ar radiometric dating.

Resolving impact volatilization and condensation from target rock mixing and hydrothermal overprinting within the Chicxulub impact structure

This work presents isotopic data for the non-traditional isotope systems Fe, Cu, and Zn on a set of Chicxulub impactites and target lithologies with the aim of better documenting the dynamic processes taking place during hypervelocity impact events, as well as those affecting impact structures during the post-impact phase. The focus lies on material from the recent IODP-ICDP Expedition 364 Hole M0077A drill core obtained from the offshore Chicxulub peak ring. Two ejecta blanket samples from the UNAM 5 and 7 cores were used to compare the crater lithologies with those outside of the impact structure. The datasets of bulk Fe, Cu, and Zn isotope ratios are coupled with petrographic observations and bulk major and trace element compositions to disentangle equilibrium isotope fractionation effects from kinetic processes. The observed Fe and Cu isotopic signatures, with δ56/54Fe ranging from −0.95‰ to 0.58‰ and δ65/63Cu from −0.73‰ to 0.14‰, mostly reflect felsic, mafic, and carbonate target lithology mixing and secondary sulfide mineral formation, the latter associated to the extensive and long-lived (>105 years) hydrothermal system within Chicxulub structure. On the other hand, the stable Zn isotope ratios provide evidence for volatility-governed isotopic fractionation. The heavier Zn isotopic compositions observed for the uppermost part of the impactite sequence and a metamorphic clast (δ66/64Zn of up to 0.80‰ and 0.87‰, respectively) relative to most basement lithologies and impact melt rock units indicate partial vaporization of Zn, comparable to what has been observed for Cretaceous-Paleogene boundary layer sediments around the world, as well as for tektites from various strewn fields. In contrast to previous work, our data indicate that an isotopically light Zn reservoir (δ66/64Zn down to −0.49‰), of which the existence has previously been suggested based on mass balance considerations, may reside within the upper impact melt rock (UIM) unit. This observation is restricted to a few UIM samples only and cannot be extended to other target or impact melt rock units. Light isotopic signatures of moderately volatile elements in tektites and microtektites have previously been linked to (back-)condensation under distinct kinetic regimes. Although some of the signatures observed may have been partially overprinted during post-impact processes, our bulk data confirm impact volatilization and condensation of Zn, which may be even more pronounced at the microscale, with variable degrees of mixing between isotopically distinct reservoirs, not only at proximal to distal ejecta sites, but also within the lithologies associated with the Chicxulub impact crater.

A reconstruction of the early Palaeocene palaeovegetation of Turtle Mountain, south-western Manitoba, Canada

The lower Goodlands Member of the Turtle Mountain Formation is exposed in a streambank outcrop on the western flank of Turtle Mountain, south-western Manitoba, Canada (49°0′2″N, 100°14′51″W). This outcrop was sampled for a 1.5 m section of microfossil-rich non-marine clay and coal-rich sediments deposited in a coastal plain environment during the early Palaeocene. These sediments were deposited 65.4–65 Ma and thus offer an opportunity to reconstruct terrestrial palaeoecology 0.6 to 1 Ma after the Cretaceous–Paleogene boundary (K–Pg) extinction event. We use quantitative palynology to reconstruct terrestrial plant ecology and explore ecological patterns of recovery and succession of these communities on a millennial time scale. Quantitative palynological analyses shows that at the time of deposition of the Goodlands Member the landscape on the coastal plain of the Western Interior Seaway – in what is now south-western Manitoba – was covered in a forested canopied swamp with tall standing swamp cypress and other conifers, Juglandaceae (walnut family), birch, alder, elms and other angiosperms, with an understory of ferns and ground cover of Sphagnum moss. Notably, palms were present but scarce, indicating a relatively warm climate. No successional pattern of diversity and community composition is evident in the samples; all samples showed high plant diversity (33–54 taxa/sample, H′ 2–3). Vegetation in Manitoba recovered within 0.6 to 1 Ma following the K–Pg extinction event or was predominantly influenced by local environmental patterns independent of time.

Conifer-mixed tropical rainforest in the Indian Paleogene: New evidences from terpenoid signatures

The Paleocene sediments from Barsingsar lignite mine section of Bikaner-Nagaur Basin in Rajasthan, India were subjected to gas chromatography–mass spectrometry (GC–MS) analysis to resolve its botanical history in relation to its terpenoid composition. The terpenoid suite was characterised by sesquiterpenoids, diterpenoids, and sporadic triterpenoids. The presence of sesquiterpenoids along with drimane, norcadalenes, cadalenes and their related compounds hint to higher plant input. High abundance of diterpenoids and their temporal universality imply a significant gymnosperm input. The diterpenoid-class of terpenoids, primarly comprises of conifer-derived abietane, phyllocladane, kaurane, pimarane/isopimarane and podocarpane-class compounds. It further point to Southern Hemisphere conifer families, Podocarpaceae and Araucariaceae. Exceptional void of phenolic abietane and labdane derivatives rule out the probability of Pinaceae as the source of these terpenes. A very low abundance of pentacyclic terpenoids like oleanane-derivatives suggest low angiosperm-derived terpenoid contribution. The average value of pristane/phytane in the realm, 1.7 indicated oxic to suboxic depositional setting. The values of ar-AGI (aromatic Angiosperm/Gymnosperm Index), t-AGI 1 and t-AGI 2 spans over 0.01 to 1, 0.009 to 1.23, and 0.002 to 0.34 respectively for the section. The research provided evidence of the occurrence of a tropical rainforest where conifers were a significant element or remained a refugia in the midst of emerging angiosperms as life stabilized in the Paleogene after the devastating Cretaceous-Paleogene (K/Pg) boundary.

New mammals from the Naskal intertrappean site and the age of India’s earliest eutherians

The first Cretaceous mammals described from India were recovered from the Naskal locality, on the southeastern edge of the Deccan Traps Volcanic Province (DTVP), where it is preserved between two basalt flows. Because the DTVP eruptions spanned the Cretaceous-Paleogene boundary (KPB), it is often unknown whether trap-associated fossil sites are latest Cretaceous (Maastrichtian) or early Paleocene in age. The Naskal locality accounts for nearly half of published mammal records from DTVP-associated sediments as well as a host of other vertebrate microfossils. Its age takes on singular importance in the context of mammalian evolution in India and the effects of the end-Cretaceous mass extinction and subsequent evolutionary radiation of placentals. Here we describe two new mammal species, Indoclemensia naskalensis gen. et sp. nov. and I. magnus sp. nov., from Naskal and present evidence from 40 Ar/ 39 Ar geochronology, magnetostratigraphy, and chemostratigraphy of the over- and underlying basalt flows to refine the age of the Naskal locality and nearby Rangapur locality. In conjunction with palynostratigraphy and vertebrate biostratigraphy, these sites can be confidently restricted to a <100 kyr interval spanning the KPB. The most probable 40 Ar/ 39 Ar age is latest Cretaceous (66.136–66.056 Ma), but an earliest Paleogene age cannot be ruled out. We explore the implications of this age assignment for Deccan chemostratigraphy and Deccan volcanism, Cretaceous-Paleogene (K/Pg) mass extinction, Indian mammalian faunal evolution, and the timing of the origin of placental mammals. • New 40 Ar/ 39 Ar geochronology, magnetostratigraphy, chemostratigraphy, and palynofloras from the Naskal and Rangapur sites. • Age of Naskal and Rangapur are likely Maastrichtian, constrained to within 100 kyr of the Cretaceous-Paleogene boundary. • Two new eutherian mammal species from the Naskal site of India are described. • These sites are ‘transitional’ distinctive in biotic composition from older and younger infra - and intertrappean localities.

Massive perturbations to atmospheric sulfur in the aftermath of the Chicxulub impact

SignificanceSulfur isotopes confirm a key role for atmospheric sulfur gases in climatic cooling, mass extinction, and the demise of dinosaurs and other global biota after the Chicxulub bolide impact at the Cretaceous-Paleogene boundary. The sulfur isotope anomalies are confined to beds containing ejecta and, in the immediately overlying sediments, are temporally unrelated to known episodes of volcanism that also bracket this event, further addressing the controversial role of the Deccan Traps in the extinction.

Innovation and Emerging Roles of Populus trichocarpa TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR Transcription Factors in Abiotic Stresses by Whole-Genome Duplication.

The TEOSINTE BRANCHED1/CYCLOIDEA/PROLIFERATING CELL FACTOR (TCP) family proteins are plant-specific transcription factors that have been well-acknowledged for designing the architectures of plant branch, shoot, and inflorescence. However, evidence for their innovation and emerging role in abiotic stress has been lacking. In this study, we identified a total of 36 TCP genes in Populus trichocarpa, 50% more than that in Arabidopsis (i.e., 24). Comparative intra-genomes showed that such significant innovation was mainly due to the most recent whole genome duplication (rWGD) in Populus lineage around Cretaceous-Paleogene (K-Pg) boundary after the divergence from Arabidopsis. Transcriptome analysis showed that the expressions of PtrTCP genes varied among leaf, stem, and root, and they could also be elaborately regulated by abiotic stresses (e.g., cold and salt). Moreover, co-expression network identified a cold-associated regulatory module including PtrTCP31, PtrTCP10, and PtrTCP36. Of them, PtrTCP10 was rWGD-duplicated from PtrTCP31 and evolved a strong capability of cold induction, which might suggest a neofunctionalization of PtrTCP genes and contribute to the adaptation of Populus lineage during the Cenozoic global cooling. Evidentially, overexpression of PtrTCP10 into Arabidopsis increased freezing tolerance and salt susceptibility. Integrating co-expression network and cis-regulatory element analysis confirmed that PtrTCP10 can regulate the well-known cold- and salt-relevant genes (e.g., ZAT10, GolS2, and SOS1), proving that PtrTCP10 is an evolutionary innovation in P. trichocarpa response to environmental changes. Altogether, our results provide evidence of the rWGD in P. trichocarpa responsible for the innovation of PtrTCP genes and their emerging roles in environmental stresses.

Hot atmospheric formation of carbonate accretionary lapilli at the Cretaceous-Paleogene boundary, Brazos River, Texas, from clumped isotope thermometry

Abstract The Chicxulub impact (in the northern Yucatan Penninsula, Mexico) marks the Cretaceous-Paleogene (K-Pg) boundary and is implicated in one of the five major extinctions. Researchers have examined ejecta from the Chicxulub impact, and most recently a drill core from the crater itself, yet the processes and chemical reactions occurring in the impact vapor plume are poorly constrained. Rounded carbonate particles, identified as accretionary lapilli, have been found thousands of kilometers from the impact crater and may be a unique record of plume conditions. We present carbon (δ13C), oxygen (δ18O), and clumped (Δ47) isotope ratios of lapilli from the Brazos River, Texas (USA), as well as from foraminifera and a mudstone. Unaltered lapilli δ13C and δ18O values covary, ranging from −9.38‰ to −2.10‰ and from −7.72‰ to −5.36‰, respectively, and they are distinct from mudstones, foraminifera, and secondarily altered lapilli in the same section. Clumped isotope temperatures [T(Δ47)] from the lapilli range from 66 °C to 539 °C and average 155 ± 46 °C (1 standard deviation), with sedimentary and fossil carbonates recording clement, shallow ocean–like T(Δ47). These data are consistent with petrography and hypothesized vapor plume formation, and we argue that the δ13C and δ18O values result from target rock decarbonation. Atmospheric temperatures &amp;gt;100 °C extending &amp;gt;1800 km from the Chicxulub crater imply an uninhabitable zone within seconds to minutes of the impact that was 10× larger in diameter than the crater itself.

Deccan volcanic activity and its links to the end-Cretaceous extinction in northern China

The Cretaceous-Paleogene (K-Pg) boundary mass extinction is commonly attributed to the Chicxulub impact and/or the Deccan Traps (DT) volcanism, but the underlying trigger remains uncertain. The lack of detailed identification of the DT eruptive pluses impedes the full assessment of their relationship to the K-Pg boundary mass extinction. Here we present the first mercury (Hg) chemostratigraphy records on the paleo Asian plate, coupled with climatic and biotic data, to constrain the effects of the DT on the Late Cretaceous climate change and mass extinction. In northern China, a total Hg (THg) spike follows warming caused by the DT volcanism and corresponds to the significant species losses. Our study suggests that this most intense pulse of the DT (~50 kyr duration) occurred just before the K-Pg boundary and suggests that it contributed to the end-Cretaceous mass extinction in northern China. • The first mercury (Hg) concentration and isotope record of the Cretaceous-Paleogene (K-Pg) boundary in the paleo Asian plate. • Hg anomaly close to the K-Pg boundary derived from a volcanic source coupling with biotic losses. • Deccan Traps LIP volcanism contributed to the end-Cretaceous mass extinction in northern China.

New Diminutive Eocene Lizard Reveals High K-Pg Survivorship and Taxonomic Diversity of Stem Xenosaurs in North America

We describe a new diminutive early Eocene lizard, Blutwurstia oliviae, gen. et sp. nov., on the basis of associated cranial and postcranial remains from the Clarks Fork Basin of Wyoming. Results from phylogenetic analyses suggest that B. oliviae is on the stem of knob-scaled lizards (Xenosaurus), a relict extant clade of specialized, stenotopic crevice-dwellers from Mexico and Central America. Results further suggest that B. oliviae is basal to all other previously described pan-xenosaurs (members of Pan-Xenosaurus, the total clade of Xenosaurus) except species of Entomophontes, to which it is closely related. Given that B. oliviae and Entomophontes are known from a limited fossil record, with only one recovered element (the maxilla) in common, the level of support for this relationship is surprisingly high. We use a posteriori time-calibrated trees and ghost lineages (maximum parsimony) and divergence time estimates under the fossilized birth-death process (Bayesian inference) to infer patterns of extinction across the Cretaceous-Paleogene (K-Pg) boundary in Pan-Xenosaurus, including those consistent with pseudoextinction. Whereas the fossil record documents a single lineage in the latest Cretaceous, results from analyses using these analytical methods suggest that three or more species existed, with high survivorship across the K-Pg boundary. The surviving lineages were apparently present at proximal to intermediate distance from the Chicxulub impact site, thought to have a causal relationship with extinctions across the K-Pg boundary. The premaxilla and dorsal vertebrae of E. incrustatus and B. oliviae, respectively, independently suggest that each of these taxa had a depressed body form consistent with extant crevice-dwelling squamates, which may have played a role in the high survivorship of pan-xenosaur lineages across the K-Pg boundary.

Unraveling the record of a tropical continental Cretaceous-Paleogene boundary in northern Colombia, South America

The Cretaceous-Paleogene (K-Pg) boundary event, triggered by the Chicxulub asteroid impact in Mexico ∼66 Myr ago, is recognized as one of the major environmental crises in Earth's history. Its effects on the evolution of tropical vegetation were drastic, giving rise to the closed-canopy tropical rainforest. Despite of its importance, the actual K-Pg boundary event layer has not yet been identified in terrestrial sections within tropical latitudes. Here, we study a sediment core (Diablito-1) from northern Colombia and described its lithofacies, palynostratigraphic content, magnetic susceptibility and geochemical composition, including the concentration of key elements linked to a meteoritic contribution such as iridium. We found an 8.2 cm-thick (0.27 inches) interval with gravel-size calcareous intraclasts, broken skeletal fragments and siliceous spherules that were transported during a short-duration high-energy event into the coastal plain. Very fine-to medium-grained spherules, concentrated in several layers of the flow structure, could be interpreted as derived from the K-Pg impact event. This thin intraclastic packstone interval lies within the extinction level of the palynomorph Echimonocolpites franciscoi, an important biostratigraphic event associated with the K-Pg boundary in Colombia. In addition, this layer is associated with both a small iridium anomaly and high concentration of several other major and trace elements that are occurring above a low Magnetic Susceptibility (MS) interval and within the initial phase of a high MS interval. These lines of evidence support the position of the K-Pg event layer within the thin interval that includes the spherules in the Diablito-1 core.

The Evolution and Fossil Record of Palaeognathous Birds (Neornithes: Palaeognathae)

The extant diversity of the avian clade Palaeognathae is composed of the iconic flightless ratites (ostriches, rheas, kiwi, emus, and cassowaries), and the volant tinamous of Central and South America. Palaeognaths were once considered a classic illustration of diversification driven by Gondwanan vicariance, but this paradigm has been rejected in light of molecular phylogenetic and divergence time results from the last two decades that indicate that palaeognaths underwent multiple relatively recent transitions to flightlessness and large body size, reinvigorating research into their evolutionary origins and historical biogeography. This revised perspective on palaeognath macroevolution has highlighted lingering gaps in our understanding of how, when, and where extant palaeognath diversity arose. Towards resolving those questions, we aim to comprehensively review the known fossil record of palaeognath skeletal remains, and to summarize the current state of knowledge of their evolutionary history. Total clade palaeognaths appear to be one of a small handful of crown bird lineages that crossed the Cretaceous-Paleogene (K-Pg) boundary, but gaps in their Paleogene fossil record and a lack of Cretaceous fossils preclude a detailed understanding of their multiple transitions to flightlessness and large body size, and recognizable members of extant subclades generally do not appear until the Neogene. Despite these knowledge gaps, we combine what is known from the fossil record of palaeognaths with plausible divergence time estimates, suggesting a relatively rapid pace of diversification and phenotypic evolution in the early Cenozoic. In line with some recent authors, we surmise that the most recent common ancestor of palaeognaths was likely a relatively small-bodied, ground-feeding bird, features that may have facilitated total-clade palaeognath survivorship through the K-Pg mass extinction, and which may bear on the ecological habits of the ancestral crown bird.

Combined data analysis of fossil and living mammals: a Paleogene sister taxon of Placentalia and the antiquity of Marsupialia.

The Cretaceous-Paleogene (KPg) boundary, one of Earth's five major extinction events, occurred just before the appearance of Placentalia in the fossil record. The Gobi Desert, Mongolia and the Western Interior of North America have important fossil mammals occurring just before and after the KPg boundary (e.g. Prodiacodon, Deltatheridium) that have yet to be phylogenetically tested in a character-rich context with molecular data. We present here phylogenetic analyses of >6000 newly scored anatomical observations drawn from six untested fossils and added to the largest existing morphological matrix for mammals. These data are combined with sequence data from 27 nuclear genes. Results show the existence of a new eutherian sister clade to Placentalia, which we name and characterize. The extinct clade Leptictidae is part of this placental sister clade, indicating that the sister clade survived the KPg event to co-exist in ancient ecosystems during the Paleogene radiation of placentals. Analysing the Cretaceous metatherian Deltatheridium in this character-rich context reveals it is a member of Marsupialia, a finding that extends the minimum age of Marsupialia before the KPg boundary. Numerous shared-derived features from multiple anatomical systems support the assignment of Deltatheridium to Marsupialia. Computed tomography scans of exquisite new specimens better document the marsupial-like dental replacement pattern of Deltatheridium. The new placental sister clade has both Asian and North American species, and is ancestrally characterized by shared derived features such as a hind limb modified for saltatorial locomotion.