I asked the question but it was never settled. Preferences where leaning towards Corpus, Creo or Vim.
But I think I will use the source as a story element. As play starts, the bones harvested so far will have yielded some Animal (3 small bones each worth 1 pawn), Corpus (1 pawn) and Vim (a single bone worth 2 pawns).
While keeping watch for new bones to surface, one of the grogs found an old broken knife...