Science Hokkaido University team discovered ancient ocean full of squids

A Japanese research team, primarily based at Hokkaido University, has discovered that ancient oceans during the late Cretaceous period—around 70 to 100 million years ago—were dominated by squids, whose numbers surpassed those of both fish and ammonites. This finding was made possible through a new technological approach known as digital fossil mining, which involves taking circular cross-sectional images of rocks to examine their internal contents.





The researchers applied this method to rock strata from the Cretaceous period in Hokkaido. They were able to compare the abundance of squid fossils to those of fish and ammonites, which had long been considered among the most prolific marine species of the time. The analysis revealed that squid populations were, in fact, greater. Until now, very few squid fossils had been recovered due to their lack of hard body parts, which made preservation difficult. This had left gaps in understanding how squids evolved and became so widespread. The new imaging technique has helped overcome these challenges by allowing scientists to identify squid remains—particularly their small and delicate structures, such as beaks—that would have previously gone undetected.

Yasuhiro Iba, an associate professor at Hokkaido University, and fellow researchers developed the new method, in which rocks containing fossils are repeatedly polished and photographed in nanometers to digitize their internal structures in high-resolution full color. As a result, a total of 1,000 cephalopod beak fossils were found. Of them, 263 were those of squids, and 39 out of the 40 squid species were new ones. The oldest squid fossil dates back about 100 million years. No such fossil has been found in earlier geological formations, suggesting the emergence of squids during this period and their rapid diversification over about 6 million years.

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