One of my quick posts since there is not too much to say, but it is an interesting photo and one that will be of interest to the SV-POW! boys. It shows the anterior part of the tail of Mamenchisaurs on display at the Chengdu University of Technology (CDUT) in China. As you can see, one of the neural spines on the left of the picture has a large and prominent growth of bone protruding from it. Now stupidly I did not take any real notes about it, but it is not a result of distortion or just some matrix left hanging on the neural spine, but fossil bone.
Mamenchisaurus tail with pathology
I can only assume that it is either the result of a badly healed break (though if so, it must have been close to the tip of the original spine and it is odd that it has healed so badly and created such a large mass as a result), but I think it more likely that this is a result of an infection that spread inside the tail causing the build-up of ossified tissue. Clearly it was not too bad as it never spread down the neural spine nor reached the other vertebrae. An interesting little snippet though I hope.
Dave Hone's Archosaur Musings 
The Smithsonian’s Diplodocus longus has similar pathologies in the caudal neural spines, as well as fusion between a couple of caudal centra.
That’s interesting to note Tom – you don’t happen to have a photo do you? 😉 Thanks for dropping in!
Tyrannosaurs also get a similar pathological fusion of the neural spines of the proximal caudals. These are in Brochu’s Sue monograph.
There does seem to be a lot of this kind of thing about: sauropods certainly seemed to treat their tails much more cavalierly than they did their necks (and quite right too). I’m not sure what Mamenchisaurus species/specimen you have here, but there is all sorts of stuff going on in the caudals of the M. hochuanensis holotype, as shown by photos here: http://www.miketaylor.org.uk/dino/mamenchi/
No doubt much of this is preservational, but I think not all. (This is a cast, by the way, not the real thing.)