“A soft cephalopod body would not have wanted to get struck by Slimonia’s tail, but we know that octopus are capable of handling lots of spiky dangerous prey by dexterously immobilizing them with the strong tentacles,” Persons said.
He added that, unlike sea scorpions, whose fossilized shells reveal their full body size and shape, the remains of ancient cephalopods require more scientific guesswork. That's because their soft bodies do not easily fossilize.
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Clues to their existence are cephalopod shells, some of which were spiral shaped, like a snail’s, while others were swirl shaped, Persons said, “like a tall helping of soft-serve ice cream.”
“Of the swirl-shelled Silurian cephalopods — say that five times fast — a few grew to well over a meter (3.3 feet) in length,” he continued. “Like modern squid, they could have reached out with their tentacles, snagged a victim and then pulled it back into their mouths.”
It is a wonder then how many of our early vertebrate ancestors managed to dodge such predators, given Slimonia’s slashing tail and the Silurian cephalopod grabbing tentacles. Some of these ancient mammal ancestors did, however, later evolving limbs and the ability to live full time on land.