Fig. 1.

Zebrafish lack oral teeth and oral expression of the tooth marker dlx2b. (A and B) Sketches of adult A. mexicanus (A) and zebrafish (B; D. rerio), illustrating that whereas characiforms like A. mexicanus have both oral and pharyngeal teeth, cypriniforms completely lack oral teeth and retain only lower pharyngeal teeth. (C and D) Diagrams of lateral views of developing larvae of these species, illustrating the locations of dlx2b expression in developing teeth and in the pectoral fin (data from refs. 12, 19, and 29). f, pectoral fin; ot, oral tooth germs or teeth; pt, pharyngeal tooth germs or teeth.