Breakup of a long-period comet as the origin of the dinosaur extinction

The origin of the Chicxulub impactor, which is attributed as the cause of the K/T mass extinction event, is an unsolved puzzle. The background impact rates of main-belt asteroids and long-period comets have been previously dismissed as being too low to explain the Chicxulub impact event. Here, we show that a fraction of long-period comets are tidally disrupted after passing close to the Sun, each producing a collection of smaller fragments that cross the orbit of Earth. This population could increase the impact rate of long-period comets capable of producing Chicxulub impact events by an order of magnitude. This new rate would be consistent with the age of the Chicxulub impact crater, thereby providing a satisfactory explanation for the origin of the impactor. Our hypothesis explains the composition of the largest confirmed impact crater in Earth’s history as well as the largest one within the last million years. It predicts a larger proportion of impactors with carbonaceous chondritic compositions than would be expected from meteorite falls of main-belt asteroids.

Dale Alan Russell (1937-2019): Voyageur of a Vanished World

We review the distinguished and varied career of our friend and colleague, palaeontologist Dr. Dale A. Russell, following the recent news of his death. Dale relished his work, and approached his research—whether it be on mosasaur systematics, dinosaur extinction, or the evolution of animal intelligence—with great gusto. A deep and contextual thinker, Dale had a penchant for metanarrative rarely equaled in these times of increased research specialization. This quality, combined with his outgoing and collaborative nature, allowed Dale to make friends and colleagues with highly varied research interests throughout the world. We remember Dale fondly, and cherish the opportunity to share the stories of his adventures (and misadventures) across the globe.

Dinosaur diversification rates were not in decline prior to the K-Pg boundary

Determining the tempo and mode of non-avian dinosaur extinction is one of the most contentious issues in palaeobiology. Extensive disagreements remain over whether their extinction was catastrophic and geologically instantaneous or the culmination of long-term evolutionary trends. These conflicts have arisen due to numerous hierarchical sampling biases in the fossil record and differences in analytical methodology, with some studies identifying long-term declines in dinosaur richness prior to the Cretaceous–Palaeogene (K-Pg) boundary and others proposing continued diversification. Here, we use Bayesian phylogenetic generalized linear mixed models to assess the fit of 12 dinosaur phylogenies to three speciation models (null, slowdown to asymptote, downturn). We do not find strong support for the downturn model in our analyses, which suggests that dinosaur speciation rates were not in terminal decline prior to the K-Pg boundary and that the clade was still capable of generating new taxa. Nevertheless, we advocate caution in interpreting the results of such models, as they may not accurately reflect the complexities of the underlying data. Indeed, current phylogenetic methods may not provide the best test for hypotheses of dinosaur extinction; the collection of more dinosaur occurrence data will be essential to test these ideas further.

Osteology and phylogeny of small-bodied hadrosauromorphs from an end-Cretaceous marine assemblage

The timing of non-avian dinosaur decline is one of the most debated subjects in dinosaur palaeontology. Dinosaur faunas from the last few million years of the Mesozoic appear far less diverse than those from earlier in the Cretaceous, a trend that could suggest non-avian dinosaur extinction occurred gradually. However, the limited nature of the latest Cretaceous dinosaur record outside western North America has obscured patterns in dinosaur diversity just before the extinction. Here, I describe two associated skeletons and several isolated fossils recovered from the New Egypt Formation of New Jersey, a latest Maastrichtian unit that underlies the K–Pg boundary. The larger skeleton appears to be a small-bodied adult from a lineage outside Hadrosauridae, the dominant group of these animals during the Maastrichtian, that persisted along the eastern coast of North America. Smaller specimens are identifiable as juvenile hadrosauromorphs. These results substantiate an important assemblage of herbivorous dinosaurs from the poorly-known Cretaceous of eastern North America. The marine depositional setting for these skeletons demonstrates that proposed ecosystem preferences among hadrosauromorphs may be biased by post-mortem transportation, and the adult skeleton has implications for assessing the proposed relictual nature of Late Cretaceous eastern North American vertebrates.

Asteroid impact, not volcanism, caused the end-Cretaceous dinosaur extinction

The Cretaceous/Paleogene mass extinction, 66 Ma, included the demise of non-avian dinosaurs. Intense debate has focused on the relative roles of Deccan volcanism and the Chicxulub asteroid impact as kill mechanisms for this event. Here, we combine fossil-occurrence data with paleoclimate and habitat suitability models to evaluate dinosaur habitability in the wake of various asteroid impact and Deccan volcanism scenarios. Asteroid impact models generate a prolonged cold winter that suppresses potential global dinosaur habitats. Conversely, long-term forcing from Deccan volcanism (carbon dioxide [CO2]-induced warming) leads to increased habitat suitability. Short-term (aerosol cooling) volcanism still allows equatorial habitability. These results support the asteroid impact as the main driver of the non-avian dinosaur extinction. By contrast, induced warming from volcanism mitigated the most extreme effects of asteroid impact, potentially reducing the extinction severity.

Ecological Mechanism of Dinosaur Extinction

To analyze the reasons for the extinction of dinosaurs by applying the elimination methods, to exclude the factors that could not cause the worldwide extinction of the dinosaurs. At last obtain a conclusion that because the Ice Age had come on the Earth and caused the changing of climate that it had been becoming cold and arid from warmth and moist, and caused the phyto-group had been changing, which the Pteridophyte and gymnosperm groups fell off or died out, but the angiosperm groups had been developing and expanding. The characters of photosynthesis of producers of the biosphere had been becoming to the seasonal and regional from the perennial and global, the total of oxygen had reduced sharply in the atmosphere, the density of oxygen had declined, and finally affected the breath of dinosaurs, and led to the extinction of dinosaurs. And as the main producers of biosphere, the pteridophyte and gymnosperm groups had fallen off or died out were the mainly reasons for the creature’s extinction at the later of the Cretaceous period.

Ecological Mechanism of Dinosaur Extinction

To analyze the reasons for the extinction of dinosaurs by applying the elimination methods, to exclude the factors that could not cause the worldwide extinction of the dinosaurs. At last obtain a conclusion that because the Ice Age had come on the Earth and caused the changing of climate that it had been becoming cold and arid from warmth and moist, and caused the phyto-group had been changing, which the Pteridophyte and gymnosperm groups fell off or died out, but the angiosperm groups had been developing and expanding. The characters of photosynthesis of producers of the biosphere had been becoming to the seasonal and regional from the perennial and global, the total of oxygen had reduced sharply in the atmosphere, the density of oxygen had declined, and finally affected the breath of dinosaurs, and led to the extinction of dinosaurs. And as the main producers of biosphere, the pteridophyte and gymnosperm groups had fallen off or died out were the mainly reasons for the creature’s extinction at the later of the Cretaceous period.