So what do we know about this find?
Firstly, although it has been confirmed as plesiosaurian by staff of the National Museums of Scotland (NMS), it contributes nothing to the debate over the existence of a monster in Loch Ness. The bones are millions of years old, and Loch Ness is (in geological terms at least) very recent - only 12,000 years old or so, being a glacially excavated trough.
Secondly, it didn't originate in the loch. As the NMS staff, and also Matt Dale of 'Mr Wood's Fossils' in Edinburgh, spotted, its general appearance, and the presence of holes made by burrowing sponges, show that it has spent some time in the sea, probably as a beach pebble on a coastal outcrop such as the Jurassic of the Moray Firth coast, or somewhere further afield. Yet Loch Ness is fresh water.
I have not had the chance to examine the specimen myself, and have to rely on the photographs published in the popular press (all of which show the specimen upside-down, by the way). It is an articulated series of what look like dorsal or very worn cervical vertebrae. The zygapophyses seem rather low and flat, and the rims of the articular faces rather rounded. The specimen is heavily water-worn, and a lot of surface detail appears to have been lost.
If there is any mystery about the specimen, it is how it ended up in Loch Ness. Natural transport as a glacial erratic is unlikely given the distribution of the nearest Jurassic strata, say the NMS staff, who have been diplomatically noncommittal about how it got there.
A deliberate hoax has been suggested by several people in the media. There is indeed a long history of hoaxes associated with the Loch Ness 'monster' phenomenon, and some perpetrator may well have been willing to waste money possibly to no effect. Finds of plesiosaur bones are not very common, and it would need someone who knew something about vertebrate palaeontology to recognise them as such at the first finding and, after the specimen was put in Loch Ness, to take the risk that nobody would find it. There is no suggestion at all that Mr McSorley was knowingly involved in any such deception. Indeed, the newspaper reports quote him as cleaning off 'about an inch of green algae' which suggests that it had been lying in the water of the loch for some time. It was, moreover, sheer luck that Mr McSorley happened to find it when a Dutch tourist, who knew his fossils, was standing by. It would be possible to buy such fossils - I'd guess a specimen of this kind could sell for a couple of hundred pounds. This would make it a rather expensive, and very shallow, deception.
However, a credible alternative is that the fossil was used as a demo piece for tour groups to show what real plesiosaur bones look like, and was left behind by accident one day. This has actually happened before, in the case of a plesiosaurian limb bone in the 1980s.
It will be interesting to watch the story develop.