More Squids Than Fish in Cretaceous Period Ocean

Jiji Press

10:57 JST, August 6, 2025

TOKYO (Jiji Press) — The ancient ocean was full of squids, whose population exceeded that of fish or ammonites, a Japanese research team has found through a new method using digital technology.

The team of researchers mainly from Hokkaido University discovered a large number of squid fossils from rocks of the late Cretaceous period about 70 million to 100 million years ago using a new technique called digital fossil-mining for photographing the inside of rocks in circular slices.

Using this technique, the team examined rocks from the late Cretaceous strata in Hokkaido, comparing fossils of squids with those of fish and ammonites from the same period and estimating their populations.

It found that more squids lived in the Cretaceous period ocean than fish and ammonites, which are known to have flourished then.

Few fossils of squids with little hard tissue had been found, and the process of their evolution and success was unknown. This reflected the previous difficulty of extracting fossils of squid species, because they are small and fragile, although they may leave hard beaks.

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.