Harpegnathos ants have evolved elongate mandibles in a rather unusual fashion. Most long-jawed ants (such as this bulldog ant) got their long chops by simply stretching out their mandibles evenly, but Harpegnathos followed a different path. They took a little piece along the front of the mandible near the head and pulled it forward almost as if it were silly putty, leaving the rest more or less intact. The downward-pointing triangle near the base is the remains of the old mandibular tip.
Danum Valley Field Centre, Sabah Borneo