I guess most people interested in geology and the history of life on Earth have heard about the dramatic period boundaries of the Mesozoic.
The most well known is of course the upper boundary of the Mesozoic, the Cretaceous-Paleogene boundary which marks the demise of the dinosaurs ca 65 million years ago. This boundary is marked not only by a catastrophic extraterrestrial impact, but is also contemporaneous to massive volcanism (Deccan Traps in India) and subsequent climatic and environmental changes of these events.
Almost equally famous and marked by an even bigger mass extinction is the lower boundary of the Mesozoic, the Permian-Triassic boundary ca 251 million years ago, associated with the end-Permian mass extinction event when ca 95% of all life died out. The end-Permian event is linked to massive volcanism in Siberia and the longterm climatic and environmental consequences where so severe that the major part of the Triassic is characterised by a harsh arid hothouse climate.
Some have probably also heard of the Triassic-Jurassic boundary, ca 201 million years ago, also associated with a major mass extinction event linked to the perhaps largest large igneous province known, the Central Atlantic Magmatic Province – massive volcanism during the initial opening of the Central Atlantic – with severe climatic and environmental consequences.
Am I repeating myself? 😉
But how many have heard of the Jurassic-Cretaceous boundary ca 145 million years ago?
This less well-known period boundary is also marked by major climatic changes. At least on the northern Hemisphere. Palynological, sedimentological and geochemical studies bear witness of climatic change from predominantly arid to semi arid conditions in the latest Jurassic to more amicable humid conditions in the earliest Cretaceous of NW Europe (see e.g. our paper Lindström and Erlström, 2011 for references).
So far, this less spectacular period boundary has not been linked to any major volcanic events or extra terrestrial impacts. And now Valentin Fischer and his colleagues have published a study in PLoS ONE (read paper here) about one specific ischtyosaur that survived the less famous Jurassic-Cretaceous (J/K) mass extinction and in fact their study suggests that the J/K event hardly affected ischtyosaurs at all 😀