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Environmental changes and resulting species diversity loss have become major issues in the modern world. In order to better understand our current situation, it is necessary to look at Earth history. As a paleobiologist, I have attempted to answer questions regarding environmental changes and their ecological consequences using fossils.

The K-Pg mass extinction event is one of the “Big five” mass extinctions, in which the taxonomic diversity significantly decreased. Studying such a mass extinction event can provide important insights into the ecological and evolutionary impacts caused by rapid environmental changes. In the marine realm, the selective extinction in cephalopods, which include squids and octopuses, is an iconic example of the extinction selectivity at the K-Pg mass extinction; Both ammonoids and nautiloids, despite their similar external shells, experienced drastically different fates during this event. Ammonoids met their end, while nautiloids survived the mass extinction. While several hypotheses have been postulated in previous studies, the definitive cause of this selective extinction remains shrouded in mystery. With the application of advanced geochemical and tomographic techniques, I aim to unearth the mechanisms behind the selective extinction phenomenon among cephalopods.