Most primate incisors carry enamel on both faces. In marmosets the lower incisors have thick enamel in front and little behind, so the softer rear wears faster and the tooth self-sharpens into a chisel edge. Paired with an unusually deep jaw and a wide gape, this lets the animal anchor its upper teeth against bark and scrape upward.
The wounds are worked repeatedly. A marmoset family maintains a set of gouge sites within its range and revisits them as gum accumulates, which turns a slow-renewing resource into something close to a farmed one. Gum is hard to digest, and marmosets carry an enlarged caecum where gut microbes ferment it. In the dry caatinga, where fruit fails for months, this exudate feeding is what keeps the group in place.
A related trait often reported incorrectly is chimaerism. Marmoset twins exchange blood cells in the womb, so an individual can carry its sibling's cells; whether this extends to tissues beyond the blood-forming lineage is disputed.