When did teeth first appear? Where did they come from? ‘The origin of teeth and teeth in non-mammals’ begins by looking at similar structures in or around the mouth that function as teeth in animals such as slugs and spiders. But what about real teeth? Teeth are homologous structures that have been passed along from a common vertebrate ancestor. The best place to look for evidence of the origin of teeth is the Silurian early jawed fishes. Once teeth were in place, the focus shifted to making them work better. Enamel evolved, along with new ways of attaching tooth to jaw. There were trends toward reduction in the number, distribution, and replacement of teeth.