FIRE AND ICE: SUPER-ERUPTIONS, VOLCANIC WINTERS, THE END-TRIASSIC EXTINCTION, AND THE RISE OF DINOSAUR-DOMINANCE

Eruptions of the giant Central Atlantic Magmatic Province (CAMP) are precisely temporally linked to the end-Triassic extinction (ETE). A striking aspect of pre-ETE continental communities is geographic provinciality. Diverse crocodile-line archosaurs and other non-dinosaurs were ecologically dominant in the tropics with no dinosaurian herbivores and generally rare and relatively small carnivorous dinosaurs. Contemporaneous high-latitude areas had higher dinosaur diversity with abundant and often large dinosaurian herbivores. Only a very few crocodile-line lineages survived the ETE, and a near-global homogenization of continental assemblages ensued with herbivorous dinosaurs spreading globally and carnivorous dinosaurs becoming much larger during the CAMP episode.

Under Triassic high-CO₂ there was no polar ice, and CO₂doublings from CAMP produced a few degrees temperature increase and some tropical lethality, but how this led to higher latitude extinctions is hard to see.

While pulses of CAMP eruptions caused CO₂ doublings over 10s to 100s of thousands of years, EACH major eruption caused a severe sulfate “volcanic winter” lasting several years plausibly leading to freezing tropical temperatures. And, there were many such coolings as opposed to a few CO₂warmings.

Crocodile-line archosaurs and dinosaurs and were relatively resistant to heat induced water stress, but the former lacked insolation, while the latter had it. The lengthy super-greenhouse events allowed some crocodile-line archosaurs to escape to cooler climes, but there was nowhere to go during volcanic winters. I hypothesise that crocodile-line and other herptile extinctions resulted from extreme cold events, for which they had no adaptations. In contrast, dinosaurs and their insulated relatives, as well as burrowing forms withstood the cold spells. This hypothesis is consistent with global post-ETE faunal homogenization, when the higher latitude dinosaurs spread globally taking over the world. This hypothesis predicts that ice crystal impressions should be found in the kinds of facies that typically have reptile footprints in eastern North America deposited simultaneously with specific eruptions that occurred elsewhere in the vast CAMP area. This is a contribution to IGCP 632.

Paraphrasing Robert Frost – ice will suffice.