Squids radiated globally prior to the Cretaceous−Paleogene mass extinction

Squids (Orders Oegopsida and Myopsida) are an essential component of the modern marine ecosystem, having high biodiversity and a huge biomass. Their global distribution, owing to their elaborate locomotor systems, is a key feature that has made them a very successful group of nektonic organisms. They originated at the Early-Late Cretaceous boundary (100 Ma), but records of early squids are extremely scarce due to the low fossilization potential of their shell-less body. Squids of Cretaceous age are so far only known from the northwest Pacific Ocean; therefore, to understand their early radiation, paleobiogeographic investigations are required. Here, we discovered new oegopsid squid fossils from late Maastrichtian sediments (ca. 67 Ma) in South Dakota. These sediments were deposited in the Western Interior Seaway, a vast inland sea that existed in North America. This is the first documentation of Cretaceous squids outside the Pacific. Based on beak morphology, these fossils are assigned to two new species, Scuthoteuthis concavus sp. nov. and Fringillorostrus simplex gen. et sp. nov. The morphological similarity between the new species and contemporaneous squid taxa from the northwest Pacific Ocean suggests that they emerged from the same ancestors. Since the Western Interior Seaway is a region most distant from the northwest Pacific, our results indicate that squids had already radiated globally before the Cretaceous−Paleogene mass extinction (66 Ma).