That sounds like a really good guess. Check out:
http://courses.science.fau.edu/~jwyneken/sta/
for an extremely detailed account of sea turtle anatomy.
Under the skeletal anatomy there are pictures of the vertebrae and I don't think they really match the pictures Steve posted, unfortunately. The vertebrae look much more complicated, more like our own. I couldn't find any pictures of nerves coming out of a turtle spinal cord, to possibly explain what the big tubes coming out of the bones in the pictures were. Hmmm...very interesting. Do we know whether it just washed ashore or was dragged up in a trawl?
Cheers!
EDIT:
I was a little unsure about what I posted above as the previous website never explicitly stated which part the cervical vertebrae were (since the pictures included an atlas vertebrae I figured it was just the whole backbone, which in retrospect was silly as it only had 7 bones in it which wouldn't really be enough. Interesting factoid: humans and giraffe, and I guess sea turtles as well now, all have the same number of bones in their neck, 7!).
Here:
http://tofino.ex.ac.uk/euroturtle/bones/skel.htm has an overall break down of the skeletal system. Though it is simple, it shows that the cervial vertebrae go from the head to the shell. While the vertebrae passes under the shell, it looks like the bone structure becomes very different. Coming out of the shell, it again turns more complicated to form the caudal vertebrae (I think). Pictures of the caudal vertebrae can be seen in the first link.
So I take back what I have said, this could be the vertebrae from underneith the shell of a sea turtle. Now the question is, can the vertebrae become detached from the shell without coming apart? Very fascinating!
