Evrim Yazgin
Cosmos science journalist
A new, advanced technique for studying fossils has revealed that squids evolved more than 50 million years earlier than previously thought and dominated Earth’s ancient seas.
Cephalopods – the group which includes squids and octopuses – first emerged about 500 million years ago (mya). Very little is known about the evolution of cephalopods over their half-a-billion-year history because soft-bodied animals rarely fossilise.
Today, squids are the most diverse and widely distributed marine cephalopods. The previous oldest squid fossils dated to about 45 mya. This led palaeontologists to suggest that the evolution and success of squids took place after the extinction event 66 mya which spelled the end of the “Age of Dinosaurs”.
Earth’s oceans during the Cretaceous period (145–66 mya) were filled with danger. While dinosaurs roamed on land, giant marine reptiles were the apex predators under the waves. There were also sharks, which had evolved about 300 million years earlier, other large predatory fish and shelled cephalopods called ammonites which reached 2.5m across.
When one thinks of the terrors of the seas, squids probably aren’t top of the list except in Lovecraftian stories.
But the new study, published in the journal Science, shows that squids were dominant hunters as early as 100 mya during the Cretaceous.
A 164-million-year-old cephalopod called Vampyronassa rhodanica discovered in 2022 is thought to be an ancestor of modern vampire squid, but is not a true squid itself.
The palaeontologists sought to overcome the lack of fossil evidence of soft-bodied animals by developing a new method for studying fossils embedded deep in ancient rock.
The technique is called grinding tomography, or “digital fossil mining”, and involves stacking photos of polished surfaces into a 3D computer-based model. The virtual model allows for detailed examination of a sample’s inner structure without further destruction.
High-resolution grinding tomography images of Cretaceous rocks in Japan revealed 263 fossilised squid beaks, with specimens from 40 species across 23 genera and 5 families.
“Our data suggest that the radical shift from heavily shelled, slowly moving cephalopods to soft-bodied forms did not result from the end-Cretaceous mass extinction,” they write. “Early squids had already formed large populations, and their biomass exceeded that of ammonites and fishes. They pioneered the modern-type marine ecosystem as intelligent, fast swimmers.”
“In both number and size, these ancient squids clearly prevailed the seas,” says first author Dr Shin Ikegami from Japan’s Hokkaido University.
“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.”
Squids became dominant swimmers and hunters at least 30 million years before marine mammals and bony fish began to stake their claim to the ancient seas.
“These findings change everything we thought we knew about marine ecosystems in the past,” says study lead Dr Yasuhiro Iba, also at Hokkaido University. “Squids were probably the pioneers of fast and intelligent swimmers that dominate the modern ocean.”