March 7, 2017 โ Shaped like a torpedo and about as swift, squids are jet-propelled underwater predators. Together with their nimble brethren, the octopus and cuttlefish, they make for an agile invertebrate armada.
But that was not always the case. Hundreds of millions of years ago, the ancestors of the tentacled trio were slow, heavily armored creatures, like the coil-shelled ammonites and the cone-shelled belemnites.
Alastair Tanner, a doctoral student at University of Bristol in England, wanted to better understand why those cephalopods lost their shells. But though both ammonites and the belemnites have left behind rich fossil records, their shell-less descendants have not.
So Mr. Tanner conducted a genetic analysis of 26 present day cephalopods, including the vampire squid, the golden cuttlefish and the southern blue-ringed octopus.