Ancient squids reigned over the oceans around 100 million years ago

The digital fossil-mining method utilizes grinding tomography to create digitized rocks and reveal hidden fossils within them (Ikegami et al., Science, June 26, 2025).

A newly developed fossil discovery method has revealed that squids first emerged and quickly became widespread, varied, and dominant in the oceans 100 million years ago, offering fresh insights into ancient marine ecosystems.

According to a new study published in the journal Science, squids emerged around 100 million years ago and rapidly became dominant predators in ancient oceans. Researchers from Hokkaido University developed an advanced fossil detection method that fully digitizes rocks and their embedded fossils in 3D. Using this technique, they discovered 1,000 fossilized cephalopod beaks within Late Cretaceous rocks in Japan. Among these delicate remains were 263 squid specimens, representing roughly 40 previously unknown species.

Because squids lack hard shells, they are rarely preserved as fossils, making their origins and early development major unresolved questions in the 500-million-year history of cephalopods—organisms often used to study long-term evolution. However, squid beaks, their durable mouthparts with a higher chance of fossilization, offer valuable insights into their evolutionary past.

One of the study’s most remarkable findings was the sheer abundance of squids in ancient oceans. The researchers discovered that squid fossils vastly outnumbered those of ammonites and bony fish. Ammonites, shelled relatives of squids, were previously thought to be among the most successful swimmers of the Mesozoic era.

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“In both quantity and size, these ancient squids clearly dominated the oceans,” said Dr. Shin Ikegami, lead author of the study and a researcher in the Department of Earth and Planetary Sciences at Hokkaido University. “They reached sizes comparable to fish and even exceeded the size of the ammonites found with them. This indicates that squids were thriving as the most abundant swimmers in ancient seas.”

The study also found that the two main types of modern squids—Myopsida, which inhabit coastal waters, and Oegopsida, which live in the open ocean—were already in existence around 100 million years ago. Previously, scientists believed squids only began to flourish after the mass extinction that wiped out the dinosaurs 65 million years ago. However, the new findings reveal that squids had already emerged and rapidly diversified well before that event.

“These discoveries completely reshape our understanding of ancient marine ecosystems,” said Associate Professor Yasuhiro Iba of Hokkaido University’s Department of Earth and Planetary Sciences, who led the research. “Squids were likely the early trailblazers of the fast, intelligent swimmers that now rule today’s oceans.”