Fig. 10

Synapomorphies are not static; they may continue to evolve. Changes in the character “upper portion of the second visceral arch” [hyomandibula, stapes] are traced on the phylogenetic tree for the Chordata (animals with notochords). Both the story and the phylogenetic tree have been substantially simplified to emphasize the idea of character origin and modification rather than the finer details of character evolution. Names in italics refer to extinct species known from fossils. Line drawings and photographs of various structures and species can be found easily on the web