Squid evolved in marine wars more than 100 million years ago

Jonathan Jackson and Zo‘ Hughes, NHMUK/University of Bristol/PA Wire

By New Scientist staff and Press Association

An evolutionary war that raged beneath the sea more than 100 million years ago created the octopus and squid, new research has shown.

Cephalopods – the tentacled creatures that include octopuses, squid and cuttlefish – possess some extraordinary traits such as instantaneous colour changing, ink squirting, jet propulsion and polarised vision.

Octopuses are also known to be highly intelligent for invertebrates and display an ability to solve complex problems.

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Until now the origins of cephalopods, which evolved from ancient marine molluscs with shells, have been shrouded in mystery.

The new research from scientists at the University of Bristol, in the UK, suggests that the octopus and its relatives developed their bizarre body plans and unusual abilities during a period of upheaval beneath the waves known as the Mesozoic Marine Revolution.

Time of dinosaurs

“On land this was the time of the dinosaurs, but beneath the seas, ecologies were changing rapidly,” says lead researcher Al Tanner. “The cephalopods are now known to have also been caught up in this major transition, evolving to lose the shells of their ancestors and develop as dynamic and uniquely adapted marine animals.”

“Fish, squid and their predators were locked in evolutionary ‘arms-races’, leading to increasingly speedy and agile predators and prey,” says Tanner.

The team compared specimens from the fossil record with evolutionary history chronicled in DNA.

A “molecular clock” technique, based on the rate at which DNA mutates naturally, was used to determine when different groups split away from each other.

“The key element of molecular clocks though is the fact that mutations steadily accumulate in genetic material over time,” says co-author Davide Pisani, also from Bristol. “So by figuring out how many mutations per million years you find, and how it may vary between different groups, we can estimate evolutionary time.”

A reduced internal skeleton helped squid and octopuses to escape predators by compressing their bodies and jetting away behind clouds of ink, say the researchers.

Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2016.2818