Harpegnathos jumping 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 their mandibles out 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.
Laboratory colony at Arizona State University