Are there different species? First, thwomps were introduced in SMB3. But in SM64 there were a bunch of new variations...you know, like the "whomps", those weird smiling gray blocks in the pyramid, the big rolling cylinder thwomp, and the happy red-cheeked platforms on the fortress level. Are some of those different species of thwomp or what?
Also, have you noticed the thwomps on Bowser's Castle in MK64? There's a GREEN one behind a cage. Has that type been in other Mario games before?