My understanding from previous threads ( http://www.glitch.com/forum/general/18283/) is that they will come out sometime in phase 2 of R2. Sometime in April or May, depending. And, they will live on Ur, necessitating that we leave our houses to gather resources. But just where they'll live on Ur remains a tantalizing mystery.
If they are wild, as opposed to semi-domesticated (pigs, butterflies, chickens), then perhaps we'll have to chase them down in order to harvest them. That would be interesting. Sloths may be good at hiding, foxes might be good at jumping and running.
ETA, perhaps they'll migrate from street to street so we can't just point to a street in UR and say "a sloth lives there, a fox lives over there." I would welcome this 'hunting' aspect to the game