Nasty surprise isn't it? a HE on the pts (Pinky) kept saying it split but I was like get out I've never seen it (SH). Then on live I had someone use a dagger special on it and hello!! 8 mobs and we all fall down ><
the pronghorn as well as the frost buffalo split if you use special attacks on them. however, the mobs spawned when they split don't drop the spellbooks, so you'll need to keep them whole if you're attempting to farm them for those.
A sps or SH can solo any group mobs that don't split, easy, I've done it 55-60ish. I don't even think either class can make the ones that split do it anyway