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

Abstract

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.

Keywords: Chicxulub; Deccan; Dinosauria; end-Cretaceous; extinction.

Fig. 1.

Geologic (A) and paleontological (B) records of the K/Pg mass extinction. Paleothermometer (A) showing the Deccan-induced warming with the two main episodes of volcanism highlighted by the black arrows and symbols of volcanoes. The last phase extends beyond the end of the Cretaceous, characterized by the bolide impact in Chicxulub. Fossil remains of non-avian dinosaurs (body fossils, egg fragments, and nesting sites) occur throughout the whole stratigraphic record of prolonged volcanism episodes (dinosaur silhouettes). Numbers represent upper Maastrichtian dinosaur bearing localities, mapped on a late Maastrichtian paleogeography in B. 1, Hell Creek Formation (United States); 2, Lameta Formation (India); 3, Tremp Formation (Spain); 4, Phosphorite beds (Morocco); 5, Marilía Formation (Brazil); 6, Nemegt Formation (Mongolia). Dinosaur silhouette image credit: Phylopic/Jack Mayer Wood, which is licensed under CC BY 3.0.

Fig. 2.

K/Pg surface temperature (degrees Celsius) outputs from GCMs. Heat maps represent temperature fluctuations from the late Maastrichtian control, with cooler temperatures in blue and warmer temperatures in red. Late Maastrichtian climate control (A) is perturbed in B by a solar dimming simulation reproducing the effect of mild asteroid impact or extreme volcanism-induced cooling (B) at 5% (scenario 1) and of a more extreme asteroid-induced cooling scenario (C) at 10% (scenario 2) of solar radiation reduction. The effect of prolonged volcanism is reproduced with an increase to 1,120 ppm of (D) CO₂ content (scenario 5) and to (E) 1,680 ppm of CO₂ (scenario 6). A transient model including both Deccan volcanism and the effect of the Chicxulub impact is shown in F (scenario 11) and G (scenario 12), and with inactive volcanism (H, scenario 13 and I, scenario 14), while the three coldest years of the impact are modeled in F (scenario 11) and H (scenario 13) (additional details and figures on GCMs are in SI Appendix). Temperature scale runs from −40 °C to 40 °C.

Fig. 3.

Ensemble habitat suitability models (averaged) projected globally for nine clades of non-avian dinosaurs (additional details and figures on habitat suitability models are in SI Appendix). Blue color represents low level of habitat suitability (0), while red color represents high habitability (1,000). Habitat suitability models trained on the late Maastrichtian record and GCMs control (A) are then projected to decoupled solar dimming scenarios with 5% (scenario 1) of solar reduction (B) and (scenario 2) 10% of solar reduction (C). A climatic scenario modeling two different levels of greenhouse enrichment due to the Deccan volcanism is reported in D (scenario 5) and E (scenario 6). The effect on the dinosaur-suitable habitats for two transient simulations with Deccan volcanism inactive (F, scenario 11 and G, scenario 12) and active (H, scenario 13 and I, scenario 14) shows the dynamic response of global dinosaur habitability during the impact (F, scenario 11 and H, scenario 13) and throughout the recovery (G, scenario 12 and I, scenario 14).

Fig. 4.

Histogram showing areal amount of habitat suitability for different ensemble HSM averaged in each climatic-forcing scenario (Sc) for all of the clades used. A constant decrease from initial conditions (control) is observed in the solar dimming models (Sc 1, 5% and Sc 2, 10%). A habitability increase is caused by ×4CO₂ (Sc 5) and ×6CO₂ (Sc 6) addition. A transient model shows the habitability decrease during the impact-related climatic perturbation and consequent recovery without Deccan volcanism (Sc 11 and 12) and with active volcanism (Sc 13 and 14). (Inset) Maximum thresholds of HSM outputs projected in each Sc.