The best article I found was this one. In it it says among other things that:
Kanzi, an unusually intelligent Bonobo chimp trained at Georgia State
University, was remarkable in that he learned to use around 200
symbols on a portable electronic symbol board, a computer with buttons
in the shape of absolute arbitrary symbols rather than manual signs.
I think you are confused about what erect limbs means, monotremes have erect hindlimbs. Erect is not the same as pillar erect (which is exceedingly rare) Just because a limb is bent or a joint can rotate does not mean it is not an erect limb. More importantly terms like semi-erect don't actually mean much, it is a weak gradation not discrete categories. ...