STAAB, KL*; HERNANDEZ, LP; George Washington University: Evolutionary developmental biology of the kinethmoid: Using zebrafish to investigate the development and evolution of a unique mechanism of premaxillary protrusion

The use of the zebrafish in the study of craniofacial development has yielded an enormous amount of data relevant to biomedical research. Thus the majority of the work on this species has examined morphological features found not only in most fishes, but nearly all vertebrates. Such emphasis ignores some of the truly exceptional craniofacial adaptations seen within the speciose Cyprinidae, the family to which the zebrafish belongs. In particular, cyprinids are characterized by a number of unique feeding adaptations that may have played a major role in the massive radiation seen within this group. The myriad reasons that make the zebrafish especially well-suited to developmental studies also make it appropriate for comparative studies with related species. Cyprinids are characterized by a novel ossification of the ethmoid region known as the kinethmoid. This kinethmoid plays a key role in premaxillary protrusion within these species. Premaxillary protrusion has been hypothesized to significantly improve feeding performance, and has evolved at least twice in different lineages. While much work has examined premaxillary protrusion within Acanthopterygii, cyprinids display a unique mode of premaxillary protrusion. Using standard histology, cleared and stained specimens and immunohistochemistry we describe the early development of this novel ossification within zebrafish. A survey of the Cyprinidae showed significant diversity in the structure of this element. Surprisingly, even within the genus Danio there was a significant degree of variation within the structure of the kinethmoid. Studies investigating the functional morphology of this novel skeletal element are ongoing.