TOKYO – A research team at a Japanese university has found that the world’s oceans during the Cretaceous period, roughly 70 million to 100 million years ago, were dominated by squid.
In a report published recently in the journal Science by the researchers from the Department of Earth and Planetary Sciences at Hokkaido University, evidence suggested that squid far outnumbered ammonites and fish — the opposite of previous assumptions.
Being soft-bodied creatures, squid rarely fossilized, with typically only their beaks remaining after decomposition.
The team developed a technique to digitally produce three-dimensional recreations of even the tiniest fossils by repeatedly photographing rock slices just one-hundredth of a millimeter thick.
Analyzing Cretaceous period rocks found on Japan’s northern main island of Hokkaido, the team identified 263 fossils of squid beaks, averaging about 4 mm in length.
Based on the shapes of the beaks, the team was able to classify the squid into 40 species, some of which were similar to modern squid.
Observations of rocks from different periods suggest that squid appeared around 100 million years ago and diversified rapidly over the course of around 6 million years.
It is believed that their population grew so much that it surpassed that of the prosperous ammonites.
In contrast to the shelled ammonites, their fellow cephalopods, squid are thought to have evolved fast swimming abilities and intelligence that were advantageous for catching food, according to the team.
Squid established their position in the marine ecosystem earlier than fish and whales, diversified after the mass extinction event at the end of the Cretaceous period, and have remained a central presence to this day, it said.