End Of The Cretaceous Research Articles

Developments in the stratigraphy of the Deccan Volcanic Province, peninsular India

The Deccan Volcanic Province has been considered as one of the largest magmatic regions, involving an aerial coverage of ca. 500,000 km2. It is subdivided into four sub-provinces, and holds a unique position in global tectonic models for understanding earth's geodynamics and the impact of voluminous eruptions on the contemporary biosystem and climate system. Published stratigraphic data suggest that volcanic eruption took place from 69 to 64 million years (Ma) ago when the Indian plate passed over the Réunion hotspot. The main phase of volcanic activity consisting of about 80% of total basaltic lava, erupted rapidly, during a short span (<1 Ma) or even less (two or three hundred thousand years), close to chron 29R, straddling to the Cretaceous–Paleogene (K–Pg) boundary. Recent high-precision age data show that the main volcanic phase is genetically linked to the Chicxulub impact and plume-head of the hotspot, and largely contributed to the end-Cretaceous mass extinction. To assess the links of the province to the K–Pg boundary, Chicxulub impact, Réunion plume, and Late Cretaceous global climate crisis, it is crucial to have a current state of knowledge of the understanding of its stratigraphy. A review of published data shows a surge in the province research that has considerably advanced the understanding of its stratigraphy. This province is intercalated with numerous infra- and intertrappean sedimentary beds that have yielded diverse biota, providing a reliable relative time control for duration of the volcanic activity. This paper presents a review of the stratigraphic developments of the province (lithostratigraphy, chemostratigraphy, magnetostratigraphy, and chronostratigraphy) from the very beginning to the present, and discusses the role of the Réunion plume in its formation.

Spatiotemporal Distributions of Non-ophidian Ophidiomorphs, With Implications for Their Origin, Radiation, and Extinction

Non-ophidian ophidiomorphs, colloquially referred to as ‘dolichosaurs,’ are small-bodied aquatic lizards that lived in shallow seaways, rivers, and reef environments during the Late Cretaceous. Preservational, geographic, and taphonomic biases in this group make trends in biodiversity difficult to assess. This is exemplified by the fact that the majority of the described species are monotypic and known only from single specimens, imparting very little information on morphological or spatial variation. Here we present a revision of the spatial and temporal distributions of non-ophidian ophidiomorph lizards (‘dolichosaurs’) from Cretaceous sediments worldwide. The fossil record of dolichosaurs begins in the Valanginian (Early Cretaceous). The late Early Cretaceous records are sparse but suggest a wide geographic distribution spanning the Tethys and Western Pacific. This is followed by a dense Cenomanian record from Tethyan and British deposits, and rarer specimens from North America. Though there is a substantial drop in the number of specimens recorded from the Turonian-Maastrichtian, these rare occurrences represent the largest geographical distribution of dolichosaurs: spanning Europe, North America, and South America before going extinct during the end-Cretaceous mass extinction. These occurrences indicate that ophidiomorphs most likely originated in the Jurassic Tethys and continued to radiate spatially and phylogenetically until the end of the Mesozoic, showing much more temporally and environmentally diverse patterns than previously indicated.

Fossil evidence reveals how plants responded to cooling during the Cretaceous-Paleogene transition

BackgroundAround the Cretaceous-Paleogene (K-Pg) boundary, an obvious global cooling occurred, which resulted in dramatic changes in terrestrial ecosystems and the evolutionary trends of numerous organisms. However, how plant lineages responded to the cooling has remained unknown until now. Between ca. 70–60 Ma Mesocyparis McIver & Basinger (Cupressaceae), an extinct conifer genus, was distributed from eastern Asia to western North America and provides an excellent opportunity to solve this riddle.ResultsHere we report a new species, Mesocyparis sinica from the early Paleocene of Jiayin, Heilongjiang, northeastern China. By integrating lines of evidence from phylogeny and comparative morphology of Mesocyparis, we found that during ca.70–60 Ma, the size of seed cone of Mesocyparis more than doubled, probably driven by the cooling during the K-Pg transition, which might be an effective adaptation for seed dispersal by animals. More importantly, we discovered that the northern limit of this genus, as well as those of two other arboreal taxa Metasequoia Miki ex Hu et Cheng (gymnosperm) and Nordenskioldia Heer (angiosperm), migrated ca.4–5° southward in paleolatitude during this time interval.ConclusionsOur results suggest that the cooling during the K-Pg transition may have been responsible for the increase in size of the seed cone of Mesocyparis and have driven the migration of plants southwards.

Biostratigraphy and geochemistry of the Cretaceous-Paleogene (K/Pg) and early danian event (Dan-C2), a possible link to deccan volcanism: New insights from Red Sea, Egypt

The end of the Cretaceous is a dramatic period in the Earth's history, when a catastrophic event known as the Cretaceous-Paleogene mass extinction event took place (66.043 ± 0.011 Ma). During the early Danian a minor hyperthermal event, known as Dan-C2 event, was raised and caused a minor perturbation in the carbon cycle. These two events were coincident with the second and the last phases of Deccan eruption in India. In El-Beida section, Quseir area, Red Sea, Egypt, the (K/Pg) is placed in the middle part of Dakhla Formation on the contact between the Hamama and Beida Member and is determined based on the high occurrence HO of Nerphrolithus frequens (CC26), the abrupt shift in δ13Corg from −23.5‰ to −24.3‰, and Hg enrichment was observed just below KPB; the Hg reaches 63.5 ppb, the earliest Danian zones (NP1, lower part of NP2, P0 and P1a) are missing due to the KPB hiatus. Dan-C2 is placed at the top of the Cretaceous-Paleogene boundary hiatus, and coincident to the base of NP2 nannofossil biozone. In general, only the second carbon isotope spike of the Dan-C2 is present and is characterized by 1.5‰ negative shift in organic carbon isotope, a sudden drop in TOC content, and mercury enrichment coincident with the δ13Corg onset that may be linked to the Deccan volcanic eruption (phase-3).

Constraints on the volume and rate of Deccan Traps flood basalt eruptions using a combination of high-resolution terrestrial mercury records and geochemical box models

Deccan Traps continental flood basalt eruptions spanned the Cretaceous-Paleogene mass extinction, erupting over a million cubic kilometers of basalt over a total duration of approximately a million years. The environmental consequences of flood basalt eruptions depend on the timing and amount of volatile release; eruption rates are thus needed to evaluate their potential to cause climate change. Radioisotopic dates are not currently sufficient to resolve sub-ten thousand year eruptive tempos, necessary for constraining the effects of short-lifetime volatiles including sulfur dioxide. Recent studies have demonstrated that increases in mercury concentration in sedimentary records correlate with flood basalt eruptions under some circumstances. However, mercury concentrations have primarily been used to show the presence or absence of flood basalt eruptions. We show that this proxy can be used to quantitatively estimate eruptive rates using a mercury geochemical cycle framework. We illustrate this using new mercury chemostratigraphic records from terrestrial Cretaceous-Paleogene boundary sections in eastern Montana, USA, with multiple high-resolution chronologic constraints. We estimate that Deccan eruptions lasted on the order of centuries and released 500–3000 megagrams (Mg) of mercury per year, corresponding to ∼50–250 km3/a of lava. The box model framework highlights the importance of carefully accounting for differences in sedimentation rate and sampling resolution when comparing mercury records from different locations and depositional environments. While there are uncertainties in the box model estimates due to possible variation in flood basalt mercury emissions and sedimentation rates, they provide a useful framework to quantitatively evaluate the global mercury budget change indicated by changing concentration in sedimentary records. Eruptions of the estimated size would have released enough SO2, if it reached the stratosphere, to cause significant cooling for the duration of the eruption. However, given our constraints on the duration of individual eruptions, these colder periods are likely too brief to be clearly visible in most existing paleoclimate records.

Late Cretaceous-Paleocene stratigraphic and structural evolution of the central Mexican fold and thrust belt, from detrital zircon (U-Th)/(He-Pb) ages

Combined U-Pb and (U-Th)/He ages on a small sample set of Cretaceous foreland-basin sandstone from a transect of the fold-thrust belt in east-central Mexico reveal correspondence between episodes of thrust-belt exhumation with previously postulated deformational events and with at least one wedge of synorogenic sediment in the adjacent Tampico-Misantla basin. Detrital zircon U-Pb ages, sandstone petrography and multidimensional scaling analysis of the Cenomanian-Turonian Mineral de Pozos sandstone, the Coniacian Soyatal and Campanian San Felipe formations, and the Paleocene Chicontepec Formation indicate sediment sources in the Mexican Cordilleran magmatic arc of western Mexico, the accreted Guerrero arc terrane, and Mesozoic sedimentary rocks of central and western Mexico. (U-Th)/He cooling ages define into three age clusters: (1) ~136-120 Ma, (2) ~99-80 Ma, and (3) ~66-56 Ma. Cooling ages are younger toward the transect's western part, which represents the interior part of the fold-thrust belt. Dominant Early Cretaceous cooling ages in the San Felipe Formation indicate lack of, or partial, resetting of the He system. Late Cretaceous cooling ages are dominant in the Soyatal Formation and are partially equivalent to their maximum depositional age (88 ± 1 Ma), suggesting derivation of grains from adjacent rapidly exhumed thrust sheets. Alternatively, these grains were partial reset. Youngest cooling ages dominate the Mineral de Pozos sandstone samples, indicating Paleocene exhumation and erosion of interior thrust sheets. The Paleocene exhumation event is equivalent to stratal ages of the lower part of the Chicontepec Formation, and sandstone composition of that unit indicates dominant sediment sources in carbonate rocks of the frontal part of the fold-thrust belt. Combined cooling ages and sandstone petrography thus indicate coeval exhumation of the entire width of the orogen in the Paleogene, rather than out-of-sequence thrust-sheet uplift and exhumation of only the interior part of the thrust wedge. Orogen-wide exhumation is corroborated by a previously published early Paleocene illite 40Ar/39Ar age of 64 ± 2 Ma for thrust deformation at the eastern flank of the Valles-San Luis Potosí carbonate platform, which formed the latest Cretaceous-Paleocene boundary between the fold-thrust belt and foreland basin in which the Chicontepec Formation was deposited.

Quantitative analysis of planktonic foraminifera across the Cretaceous-Paleogene transition and observations on the extinction horizon, Haymana Basin, Turkey

The Haymana Basin, Turkey, hosts complete record of sedimentation across the Cretaceous-Paleogene (K-Pg) boundary. To examine the K-Pg boundary transition and delineate the bioevents, two consecutive sections (UH and UKHB) were measured and sampled at high resolution. Three biozones were established: Plummerita hantkeninoides, P0 and Pα. A detailed quantitative study on planktonic foraminifera was carried out for the P. hantkeninoides and the P0 zones for 63–150 μm and >150 μm size fractions. Results show dominance of ecological generalists with small, simple tests over ecological specialists with large, robust, ornamented morphologies. Heterohelicids are the most dominant group on both size fractions throughout the late Maastrichtian, however right after the K-Pg boundary Guembelitria cretacea blooms and dominates the planktonic foraminiferal assemblage in early Danian P0 Zone. The K-Pg boundary characterizes itself as 2–3 mm thick reddish oxidized layer and its transition reveals a series of events: A rapid change in sedimentation from Maastrichtian mudstones to Danian marls. A sudden annihilation of large, ornamented ecological specialists (e.g., Globotruncana, Rugoglobigerina, Planoglobulina) right at the reddish layer (even though quantitative study revealed that there is a systematic reduction in the foraminiferal species richness throughout the P. hantkeninoides Zone). Spikes of calcareous dinoflagellate Thoracosphaera and fecal pellets right after the K-Pg boundary in the Danian P0 Zone. Anomalous increase in CaO rich spherules and amorphous grains coupled with barite crystals right at the K-Pg boundary layer. Paleobathymetric calculations also revealed approximately 400 m paleodepth for the study area corresponding the upper bathyal zone.

The early wasp plucks the flower: disparate extant diversity of sawfly superfamilies (Hymenoptera: ‘Symphyta’) may reflect asynchronous switching to angiosperm hosts

AbstractThe insect order Hymenoptera originated during the Permian nearly 300 Mya. Ancestrally herbivorous hymenopteran lineages today make up the paraphyletic suborder ‘Symphyta’, which encompasses c. 8200 species with very diverse host-plant associations. We use phylogeny-based statistical analyses to explore the drivers of diversity dynamics within the ‘Symphyta’, with a particular focus on the hypothesis that diversification of herbivorous insects has been driven by the explosive radiation of angiosperms during and after the Cretaceous. Our ancestral-state estimates reveal that the first symphytans fed on gymnosperms, and that shifts onto angiosperms and pteridophytes – and back – have occurred at different time intervals in different groups. Trait-dependent analyses indicate that average net diversification rates do not differ between symphytan lineages feeding on angiosperms, gymnosperms or pteridophytes, but trait-independent models show that the highest diversification rates are found in a few angiosperm-feeding lineages that may have been favoured by the radiations of their host taxa during the Cenozoic. Intriguingly, lineages-through-time plots show signs of an early Cretaceous mass extinction, with a recovery starting first in angiosperm-associated clades. Hence, the oft-invoked assumption of herbivore diversification driven by the rise of flowering plants may overlook a Cretaceous global turnover in insect herbivore communities during the rapid displacement of gymnosperm- and pteridophyte-dominated floras by angiosperms.

New Material of Paleocene-Eocene Pellornis (Aves: Gruiformes) Clarifies the Pattern and Timing of the Extant Gruiform Radiation

Pellornis mikkelseni is an early gruiform from the latest Paleocene-earliest Eocene Fur Formation of Denmark. At approximately 54 million years old, it is among the earliest clear records of the Gruiformes. The holotype specimen, and only material thus far recognised, was originally considered to comprise a partial postcranial skeleton. However, additional mechanical preparation of the nodule containing the holotype revealed that the skeleton is nearly complete and includes a well-preserved skull. In addition to extracting new information from the holotype, we identify and describe two additional specimens of P. mikkelseni which reveal further morphological details of the skeleton. Together, these specimens show that P. mikkelseni possessed a schizorhinal skull and shared many features with the well-known Paleogene Messelornithidae (“Messel rails”). To reassess the phylogenetic position of P. mikkelseni, we modified an existing morphological dataset by adding 20 characters, four extant gruiform taxa, six extinct gruiform taxa, and novel scorings based on the holotype and referred specimens. Phylogenetic analyses recover a clade containing P. mikkelseni, Messelornis, Songzia and crown Ralloidea, supporting P. mikkelseni as a crown gruiform. The phylogenetic position of P. mikkelseni illustrates that some recent divergence time analyses have underestimated the age of crown Gruiformes. Our results suggest a Paleocene origin for this important clade, bolstering evidence for a rapid early radiation of Neoaves following the end-Cretaceous mass extinction.

Nature and timing of biotic recovery in Antarctic benthic marine ecosystems following the Cretaceous–Palaeogene mass extinction

AbstractTaxonomic and ecological recovery from the Cretaceous–Palaeogene (K–Pg) mass extinction 66 million years ago shaped the composition and structure of modern ecosystems. The timing and nature of recovery has been linked to many factors including palaeolatitude, geographical range, the ecology of survivors, incumbency and palaeoenvironmental setting. Using a temporally constrained fossil dataset from one of the most expanded K–Pg successions in the world, integrated with palaeoenvironmental information, we provide the most detailed examination of the patterns and timing of recovery from the K–Pg mass extinction event in the high southern latitudes of Antarctica. The timing of biotic recovery was influenced by global stabilization of the wider Earth system following severe environmental perturbations, apparently regardless of latitude or local environment. Extinction intensity and ecological change were decoupled, with community scale ecological change less distinct compared to other locations, even if the taxonomic severity of the extinction was the same as at lower latitudes. This is consistent with a degree of geographical heterogeneity in the recovery from the K–Pg mass extinction. Recovery in Antarctica was influenced by local factors (such as water depth changes, local volcanism, and possibly incumbency and pre‐adaptation to seasonality of the local benthic molluscan population), and also showed global signals, for example the radiation of the Neogastropoda within the first million years of the Danian, and a shift in dominance between bivalves and gastropods.

Deposition and age of Chicxulub impact spherules on Gorgonilla Island, Colombia

AbstractThe end-Cretaceous mass extinction (66 Ma) has long been associated with the Chicxulub impact on the Yucatan Peninsula. However, consensus on the age of this impact has remained controversial because of differing interpretations on the stratigraphic position of Chicxulub impact spherules relative to the mass extinction horizon. One side argues that the impact occurred precisely at the Cretaceous-Paleogene boundary, thus coinciding with the mass extinction; the other side argues that the impact predated the Cretaceous-Paleogene boundary, based on the discovery of primary impact spherules deposits in NE Mexico and Texas near the base of planktic foraminiferal zone CF1, dated at 170 k.y. before the Cretaceous-Paleogene boundary. A recent study of the most pristine Chicxulub impact spherules discovered on Gorgonilla Island, Colombia, suggested that they represent a primary impact deposit with an absolute age indistinguishable from the Cretaceous-Paleogene boundary. Here, we report on the Gorgonilla section with the main objective of evaluating the nature of deposition and age of the spherule-rich layer relative to the Cretaceous-Paleogene boundary.The Gorgonilla section consists of light gray-yellow calcareous siliceous mudstones (pelagic deposits) alternating with dark olive-brown litharenites (turbidites). A 3-cm-thick dark olive-green spherule-rich layer overlies an erosional surface separating Maastrichtian and Danian sediments. This layer consists of a clast-supported, normally graded litharenite, with abundant Chicxulub impact glass spherules, lithics (mostly volcanic), and Maastrichtian as well as Danian microfossils, which transitions to a calcareous mudstone as particle size decreases. Mineralogical analysis shows that this layer is dominated by phyllosilicates, similar to the litharenites (turbidites) that characterize the section. Based on these results, the spherule-rich layer is interpreted as a reworked early Danian deposit associated with turbiditic currents. A major hiatus (&amp;gt;250 k.y.) spanning the Cretaceous-Paleogene boundary and the earliest Danian is recorded at the base of the spherule-rich layer, based on planktic foraminiferal and radiolarian biostratigraphy and carbon stable isotopes. Erosion across the Cretaceous-Paleogene boundary has been recorded worldwide and is generally attributed to rapid climate changes, enhanced bottom-water circulation during global cooling, sea-level fluctuations, and/or intensified tectonic activity. Chicxulub impact spherules are commonly reworked and redeposited into younger sediments overlying a Cretaceous-Paleogene boundary hiatus of variable extent in the Caribbean, Central America, and North Atlantic, while primary deposits are rare and only known from NE Mexico and Texas. Because of their reworked nature, Gorgonilla spherules provide no stratigraphic evidence from which the timing of the impact can be inferred.

Delayed calcareous nannoplankton boom-bust successions in the earliest Paleocene Chicxulub (Mexico) impact crater

AbstractThe Cretaceous-Paleogene (K-Pg; 66 Ma) mass extinction was caused by a bolide impact on the Yucatán platform near modern Chicxulub, Mexico. Calcareous nannoplankton, a dominant group of primary producers, were almost eradicated at this time. Post-impact nannoplankton assemblages from Northern Hemisphere sites were characterized by a short-lived series of high-dominance, low-diversity acmes (“boom-bust” successions), which likely represent an unstable post-impact environment. Although these boom-bust successions are a global signal, the mechanisms that controlled the taxonomic switchovers between acmes are currently unknown. Here, we present detailed analyses of calcareous nannoplankton and planktic foraminiferal assemblages in a new K-Pg section from the peak ring of the Chicxulub crater. We show that although nannoplankton assemblages resemble the typical series of acmes at Tethyan sites, the termination of the “disaster” acme in the crater is delayed by at least 500 k.y. The coincidence between shifts in the dominant planktic foraminiferal trophic group and switchovers in nannoplankton boom-bust taxa suggests that this series of acmes may represent a gradual trend toward oligotrophy driven by the global restoration of biological pump efficiency. Thus, the global diachroneity of boom-bust successions likely reflects the differential pacing of biological pump restoration between oceanic basins and settings.

Evolution: Bedbugs Evolved before Their Assumed Ancestral Host

It has long been assumed that human-parasitic bedbugs evolved from the ectoparasites of bats. However, new fossil-calibrated phylogenetic analysis places their appearance at ∼115 million years ago; before the Cretaceous-Paleogene mass extinction and ∼30 million years prior to fossil records of the first bats.

Divergence rates of subviral pathogens of angiosperms abruptly decreased at the Cretaceous-Paleogene boundary

Biogeographic distribution of infected plants and the continental drift theory allow a tentative time calibration of the phylogenetic tree of Pospiviroidae. Hypothetically, viroids evolved in the late Early Cretaceous shortly after the appearance of angiosperms, which constitute their only known hosts. No decline in the estimated divergence rates of Pospiviroidae is observed during the Late Cretaceous but it appears that they abruptly decreased at the Cretaceous-Paleogene boundary. However, an adaptive radiation of Pospiviroidae which occurred in the late Paleocene may reflect a recovery from the Cretaceous-Paleogene (K–Pg) mass extinction. It seems that the evolutionary history of viroids has been in part shaped by radiation and extinction events of angiosperms. Herein, for the first time I show the probable impact of a mass extinction event on the divergence rates of subviral pathogens, which are the simplest known “lifeforms”.

A mid-Cretaceous tyrannosauroid and the origin of North American end-Cretaceous dinosaur assemblages.

Late Cretaceous dinosaur assemblages of North America-characterized by gigantic tyrannosaurid predators, and large-bodied herbivorous ceratopsids and hadrosaurids-were highly successful from around 80 million years ago (Ma) until the end of the 'Age of Dinosaurs' 66 Ma. However, the origin of these iconic faunas remains poorly understood because of a large, global sampling gap in the mid-Cretaceous, associated with an extreme sea-level rise. We describe the most complete skeleton of a predatory dinosaur from this gap, which belongs to a new tyrannosauroid theropod from the Middle Turonian (~92 Ma) of southern Laramidia (western North America). This taxon, Suskityrannus hazelae gen. et sp. nov., is a small-bodied species phylogenetically intermediate between the oldest, smallest tyrannosauroids and the gigantic, last-surviving tyrannosaurids. The species already possesses many key features of the tyrannosaurid bauplan, including the phylogenetically earliest record of an arctometatarsalian foot in tyrannosauroids, indicating that the group developed enhanced cursorial abilities at a small body size. Suskityrannus is part of a transitional Moreno Hill (that is, Zuni) dinosaur assemblage that includes dinosaur groups that became rare or were completely absent in North America around the final 15 Myr of the North American Cretaceous before the end-Cretaceous mass extinction, as well as small-bodied forebears of the large-bodied clades that dominated at this time.

Morphospace expansion paces taxonomic diversification after end Cretaceous mass extinction.

Highly resolved palaeontological records can address a key question about our current climate crisis: how long will it be before the biosphere rebounds from our actions? There are many ways to conceptualize the recovery of the biosphere; here, we focus on the global recovery of species diversity. Mass extinction may be expected to be followed by rapid speciation, but the fossil record contains many instances where speciation is delayed-a phenomenon about which we have a poor understanding. A probable explanation for this delay is that extinctions eliminate morphospace as they curtail diversity, and the delay in diversification is a result of the time needed for new innovations to rebuild morphospace, which can then be filled out by new species. Here, we test this morphospace reconstruction hypothesis using the morphological complexity of planktic foraminifer tests after the Cretaceous-Palaeogene mass extinction. We show that increases in complexity precede changes in diversity, indicating that plankton are colonizing new morphospace, then slowly filling it in. Preliminary diversification is associated with a rapid increase in the complexity of groups refilling relict Cretaceous ecospace. Subsequent jumps in complexity are driven by evolutionary innovations (development of spines and photosymbionts), which open new niche space. The recovery of diversity is paced by the construction of new morphospace, implying a fundamental speed limit on diversification after an extinction event.

Diversity on the rebound.

The reduction in biodiversity after the end-Cretaceous mass extinction event did not instantaneously create evolutionary opportunities for planktonic protists. Survivors instead re-diversified in pulses that followed morphological innovations.

A seismically induced onshore surge deposit at the KPg boundary, North Dakota

The most immediate effects of the terminal-Cretaceous Chicxulub impact, essential to understanding the global-scale environmental and biotic collapses that mark the Cretaceous-Paleogene extinction, are poorly resolved despite extensive previous work. Here, we help to resolve this by describing a rapidly emplaced, high-energy onshore surge deposit from the terrestrial Hell Creek Formation in Montana. Associated ejecta and a cap of iridium-rich impactite reveal that its emplacement coincided with the Chicxulub event. Acipenseriform fish, densely packed in the deposit, contain ejecta spherules in their gills and were buried by an inland-directed surge that inundated a deeply incised river channel before accretion of the fine-grained impactite. Although this deposit displays all of the physical characteristics of a tsunami runup, the timing (<1 hour postimpact) is instead consistent with the arrival of strong seismic waves from the magnitude Mw ∼10 to 11 earthquake generated by the Chicxulub impact, identifying a seismically coupled seiche inundation as the likely cause. Our findings present high-resolution chronology of the immediate aftereffects of the Chicxulub impact event in the Western Interior, and report an impact-triggered onshore mix of marine and terrestrial sedimentation-potentially a significant advancement for eventually resolving both the complex dynamics of debris ejection and the full nature and extent of biotic disruptions that took place in the first moments postimpact.

A small yet occasional meal: predatory drill holes in Paleocene ostracods from Argentina and methods to infer predation intensity

AbstractOstracods are common yet understudied prey item in the fossil record. We document drill holes in Paleocene (Danian) ostracods from central Argentina using 9025 specimens representing 66 species. While the percentage of drilled specimens at assemblage‐level is only 2.3%, considerable variation exists within species (0.3–25%), suggesting prey preference by the drillers. This preference is not determined by abundance because no significant correlation is found between species abundance and drilling percentages. Seven methods were used, some of which are new, to quantify drilling percentages for the abundant and commonly drilled Togoina argentinensis. The resulting range, from 9.9% to 14.6%, suggests that drilling percentages are fairly insensitive to the method used, implying that comparisons across studies are possible. This information, combined with data from the literature, suggests the Cretaceous–Palaeogene mass extinction may have had a limited effect on drilling intensity in ostracods. The cylindrical (Oichnus simplex) and parabolic (O. paraboloides) drill holes from Argentina may have been caused primarily by naticid and possibly muricid gastropods. Two oval drill holes (O. ovalis) are morphologically similar to octopod drill holes, but their small size, the fact that extant octopods are not known to drill ostracods and the absence of such holes in co‐occurring gastropods, preclude ascription to a predator clade. Drill holes are located preferentially in the median and dorsal regions, where most soft tissue, including the adductor muscle, is located. Drilled specimens are statistically taller than non‐drilled specimens for T. argentinensis and larger predators selected larger ostracods. The drilling percentage does not significantly differ in ornamented ostracods.

Ocean Drilling Perspectives on Meteorite Impacts

Extraterrestrial impacts are a ubiquitous process in the solar system, reshaping the surface of rocky bodies of all sizes. On early Earth, impact structures may have been a nursery for the evolution of life. More recently, a large meteorite impact caused the end-Cretaceous mass extinction, causing the extinction of 75% of species known from the fossil, including non-avian dinosaurs, and clearing the way for the dominance of mammals and eventual evolution of humans. Understanding the fundamental processes associated with impact events is critical to understanding the history of life on Earth, and the potential for life in our solar system and beyond. Scientific ocean drilling has generated a large amount of unique data on impact processes. With the constant subduction and creation of oceanic crust, the Chicxulub impact is the single largest and most significant impact event that can be studied by sampling modern ocean basins. Marine sediment cores have been instrumental in quantifying the environmental, climatological, and biological effects of that impact. Drilling in the Chicxulub Crater has significantly advanced our understanding of fundamental impact processes, notably the formation of peak rings in large impact craters, but also raised new questions waiting to be addressed with further drilling. Within the crater, the nature and thickness of the melt sheet in the central basin is unknown, and an expanded Paleocene hemi-pelagic section would provide insights to both the recovery of life and the climatic changes after the impact. Globally, new cores in the Pacific could directly sample the downrange ejecta of this northeast-southwest trending impact. Extraterrestrial impacts have been controversially suggested as primary drivers for many important paleoclimatic and environmental events throughout Earth History. However, marine sediment archives and geochemical proxies (e.g., Osmium isotopes) provide a long-term archive of major impact events in recent Earth history and show that, other than the end-Cretaceous, significant environmental changes do not appear to be driven by impacts.