Origin and radiation of squids revealed by digital fossil-mining.

The evolution of soft-bodied squids, which provide a major part of the biomass in modern oceans globally, is poorly understood owing to their patchy fossil record. We provide a comprehensive evolutionary history of squids through "digital fossil-mining" techniques, revealing a new lagerstätte. The more than 250 fossil beaks of 40 species show that squids originated and rapidly radiated by 100 million years ago. Our data suggest that the radical shift from heavily shelled, slowly moving cephalopods to soft-bodied forms did not result from the end-Cretaceous mass extinction (66 million years ago). Early squids had already formed large populations, and their biomass exceeded that of ammonites and fishes. They pioneered the modern-type marine ecosystem as intelligent, fast swimmers. Editor's summary: Cephalopods are one of the most successful marine invertebrates in modern oceans, and they have a 500-million-year-old history. However, we know very little about their evolution because soft-bodied animals rarely fossilize. Ikegami et al. developed an approach to reveal squid fossils, focusing on their beaks, the sole hard component of their bodies. They found that squids radiated rapidly after shedding their shells, reaching high levels of diversity by 100 million years ago. This finding shows both that squid body forms led to early success and that their radiation was not due to the end-Cretaceous extinction event. —Sacha Vignieri [ABSTRACT FROM AUTHOR]