The pelorus, Piscisaurus sicamalus, is a small, polycotylid-like pliosaur from the open seas of the Atlantic, Indian and Pacific Ocean, in The New Dinosaurs: An Alternative Evolution.
The pelorus is a small pliosaur and, like its relatives, it feeds on ammonites. This is the only type, however, that has the ability to attack and kill the largest ammonite of the oceans, the kraken. It hunts in the warm placid waters of the doldrums, where its prey is most abundant.
There is an oily swell, and dotted here and there are the floating bulbous shapes of kraken shells, their long tentacles streaming out just below the surface, passively entrapping any small creature that happens into their entangling fibers. A splash! And a spray of water! The tranquil scene is shattered by a frenetic burst of activity around one of the bobbing shells. A pelorus has broken the surface and is wrestling with a kraken, struggling to reach its vulnerable parts. The weak tentacles loop and coil out of the water, trying to entangle the attacker, but they have little real strength. The pelorus clambers over them, wriggles through their coils, and finally plunges its sharp jaws down into the fleshy head. Again and again it stabs, until at last the tiny brain is destroyed. The writhing tentacles gradually become still, and the pelorus begins to feast, tearing off chunks of flesh as quickly as it can before the air seeps from the shell's chambers and the massive corpse sinks to the depths.