Most of us assume that ivory for key tops were from elephants, but
I believe that walrus ivory was used and maybe some other animal.
Someone with greater knowledge than I could give some detail on this.
There were many walrus available; one type of a 1990 census were
200,000.

My parents in the UK had a 'Challen' piano in the 1940s, one of the
best makes in that land, and I remember that the ivory keytops were
very highly polished, more so than most I have ever seen since on
either side of the 'Pond'.  Also, I do not remember the 'split' in the
keytop to join with the longer piece [tail].  It appeared distinctly
all one piece.

I obtained a warthog tusk some years ago, and that ivory appeared the
toughest of any.

Stephen Bentley
Vancouver, British Columbia, Canada