Recent studies (paywalled):

Summary from the Editor:

Cephalopods rank among the most thriving aquatic invertebrates in contemporary seas, boasting a history spanning 500 million years. Nonetheless, our understanding of their evolution remains limited due to the rarity of soft-bodied creatures fossilizing. Ikegami et al. devised a method to uncover squid fossils, concentrating on their beaks, which are the only hard parts of their anatomy. Their research indicated that squids diversified swiftly after losing their shells, achieving significant levels of diversity by 100 million years ago. This discovery illustrates that squid body structures contributed to their early triumph and that their diversification was not a result of the end-Cretaceous extinction event.