Soooo, I just started up my first fortress with the new version, hoping for some spectacular undead !!FUN!!, as it was set up close to a necromancers tower. Things were coming along nicely, although I as usual had neglected my defences somewhat. Anyhow, right after the arrival of the first caravan, I get notified that "the dead walk the land", and find 4 zombies at the map edge, a goblin, 2 elves and a human. Great timing I think, as the caravan guards should be able to help me to dispose of these. The zombies approach my entrance and with perfect timing coincide with the caravan, whose guards quickly dispatch them, or so I think...
Suddenly, 20 or so mussel shells spring to life from my nearby fishery, quickly kill the nearby caravan axedwarf and proceed to wreak havoc in my fortress. Shortly after the zombies who I thought dead rise again and join them, along with an undead capybara head, it's mutilated corpse and the newly killed dwarves. I couldn't bring myself to try and stop it, it was too much fun watching my dwarves run in panic from the swarm of mussel shells.
Anyway, I guess now any kind of refuse or animal remains should be considered hazardous material? The biome wasn't even evil, so didn't expect to have anything but the invading undead attacking me, and am not sure how to proceed with making my next fortress safer :>