Elasmosaurus
It was suggested by D.M.S. Watson that their method was as surface swimmers, mostly eating with their head above water, darting down to snatch smaller fish which were feeding on plankton. It is hard to see the benefit of a long neck under water. Aquatic mammals operating under water all have a streamlined torpedo-shape, as did pliosaurs and ichthyosaurs. All the longer-necked families were, from the setting of the teeth and jaws, eaters of small fish. The large number of neck vertebrae is probably linked to the modest degree of flexibility between adjacent vertebrae.