When I was a kid I saw some of these pictures and thought 'dinosaur' now that I'm an adult with biology training I only wish I could think that. Saddly they aint.
Take a good look at the 'head' look at it closely. You can see that the head may just really be a thicker lump of tissue. The spine is still apparently visible where the animals nose would be, plus the tissue itself doesn't remind me of what you would see in a head. My guess is its a whale or basking/whale shark thats just baddly decomposed.
I've seen how basking sharks decompose and they look almost exactly like a rotted plesiosaurs, at least what you would think one should look like. Most of the head area is gills which quickly rot away, leaving a small head and a long neck.
I'd LOVE for this to be a real plesiosaurs but the odds of there being a large, airbreathing marine animal is pretty damn slim at this point. I would be surprised if we don't find more living fossils in the sea and hell we may even find a dinasaur, but I can't see it being one of the mega dinosaurs. If we are really really lucky, some small lizard in some isolated area will get a geneticly classified and turn up to be closely related to dinosaurs, but I'm afraid thats the only dinosaur you will find.
Birds may in fact be part of the dinosaur genetic tree, and I think that theory is correct, but its not quite the same thing.
Also look at those yellow fibers around the 'fin' that looks a lot like whale baleen. Its visible in other shots as well.
That I found with a random google image search, looks not unlike that first picture.
Edit:blah they caught me stealing their bandwidth so that one picture is gone and I'm way to lazy to regoogle

Also I should really do these when I'm awake and not at 2AMish, ugh the typos.