Although longjaw mudsucker ( Gillichthys mirabilis , Gobiidae) has been studied extensively for its ability to occupy low‐oxygen environments, few studies have addressed the evolution of its exceptionally elongated jaws that extend posteriorly beyond the gill opening in large adults. In this study, the ontogeny of the maxillae of G. mirabilis , Gillichthys seta , and the out‐group species Eucyclogobius newberryi was studied wi...