Insights from sharks: evolutionary and developmental models of fin development.

The shark and its embryology have recently returned to the spotlight as a model animal in the quest to determine the origins of paired appendages during vertebrate evolution. As the most basal living gnathostomes, sharks and other extant chondrichthyans are ideal models to elucidate the developmental mechanisms utilised in mesoderm-derived primitive fin morphologies. Chondrichthyans occupy a phylogenetic position and possess morphological structures that can answer major questions on the origin of the body plan of vertebrates. This review will outline the past, present, and future use of shark species as a model system with particular emphasis on the recent studies that have utilised comparative molecular embryology of chondrichthyan species to examine the question of the origin of the paired fins. We will also examine the problems and pitfalls of utilising chondrichthyans and the barriers that remain to their utilisation in the modern era of developmental biology.