Origin of Jaws
Jaws evolved from the first gill arch, cartilage that supported the front gill of jawless fish.
Teeth evolved from small pointed structures that toughened the skin over the gill bars.
Jaws enabled vertebrates to become predators, opening many new ecological niches.
Jawless vertebrates were filter feeders, parasites or scavengers.
Image courtesy of Philippe Janvier, Tree of Life Project, http://tolweb.org/tree?group=Gnathostomata&contgroup=Vertebrata
Skull of a shark showing the jaws in red and the gill arches in green.