Abstract
Sepioids are an evolutionarily successful group of modern ten-armed cephalopods (Decabrachia) of high biodiversity, providing a large amount of biomass in present-day oceans. They include the internally shelled order Sepiida (cuttlefish) and the soft-bodied order Sepiolida (bobtail squid). The phylogenetic position and evolutionary history of these orders are, however, so far poorly understood due to the patchy fossil record of the Decabrachia. Here we report Uluciala rotundata gen. et sp. nov. from the upper Campanian to upper Maastrichtian (~74-67 Ma, Upper Cretaceous), South Dakota, which shows an intermediate morphology between Sepiida and Sepiolida. This discovery was facilitated by a new approach in palaeontology, the Digital fossil-mining method incorporating a zero-shot learning AI model. Uluciala rotundata demonstrates a close relationship between the two sepioid orders, which has previously been interpreted controversially. Our findings indicate that sepioids experienced an early phase of radiation in the later part of the Late Cretaceous.