Squids are rarely preserved as fossils because they don’t have hard shells. Their origin and early evolution are the biggest questions in the 500-million-year history of cephalopods, which have been model animals for long-term evolution. Squid beaks, hard mouthparts that have a high fossilization potential, are therefore important clues for studying how squids evolved.

One of the study’s most striking discoveries was how common squids were in ancient oceans. The team found that squid fossils far outnumbered those of ammonites and bony fishes. Ammonites are extinct shelled relatives of squids and have been considered among the most successful swimmers of the Mesozoic era.

Digital fossil-mining of squid beaks. (Video credit: HU)

“In both number and size, these ancient squids clearly dominated the seas,” said Dr. Shin Ikegami of the Department of Earth and Planetary Sciences at Hokkaido University, the study’s first author. “Their body sizes were as large as fish and even bigger than the ammonites we found alongside them. This shows us that squids were thriving as the most abundant swimmers in the ancient ocean.”

The research also revealed that the two main groups of modern squids, Myopsida, which live near the shore, and Oegopsida, found in the open sea, were already present around 100 million years ago. Until now, scientists believed that squids only began to flourish after the mass extinction event that ended the age of dinosaurs about 65 million years ago. The new study shows that squids had already originated and explosively diversified long before then.

“These findings change everything we thought we knew about marine ecosystems in the past,” said Associate Professor Yasuhiro Iba of the Department of Earth and Planetary Sciences at Hokkaido University, who led the study. “Squids were probably the pioneers of fast and intelligent swimmers that dominate the modern ocean.”