The extremely long necks of "plesiosauromorphs" have caused speculation as to their function from the very moment their special build became apparent. Conybeare had offered three possible explanations. The neck could have served to intercept fast-moving fish in a pursuit. Alternatively, plesiosaurs could have rested on the sea bottom, while the head was sent out to search for prey, which seemed to be confirmed by the fact the eyes were directed relatively upwards. Finally, Conybeare suggested the possibility that plesiosaurs swam on the surface, letting their necks plunge downwards to seek food at lower levels. All these interpretations assumed that the neck was very flexible. The modern insight that the neck was, in fact, rather rigid, with limited vertical movement, has necessitated new explanations. One hypothesis is that the length of the neck made it possible to surprise schools of fish, the head arriving before the sight or pressure wave of the trunk could alert them. "Plesiosauromorphs" hunted visually, as shown by their large eyes, and perhaps employed a directional sense of olfaction. Hard and soft-bodied cephalopods probably formed part of their diet. Their jaws were probably strong enough to bite through the hard shells of this prey type. Fossil specimens have been found with cephalopod shells still in their stomach. The bony fish (Osteichthyes), which further diversified during the Jurassic, were likely prey as well. A very different hypothesis claims that "plesiosauromorphs" were bottom feeders. The stiff necks would have been used to plough the sea bottom, eating the benthos. This would have been proven by long furrows present in ancients seabeds. Such a lifestyle has in 2017 been suggested for "Morturneria". "Plesiosauromorphs" were not well adapted to catching large fast-moving prey, as their long necks, though seemingly streamlined, caused enormous skin friction. Sankar Chatterjee suggested in 1989 that some Cryptocleididae were suspension feeders, filtering plankton. "Aristonectes" e.g. had hundreds of teeth, allowing it to sieve small Crustacea from the water.