Acquisition of the paired fins: a view from the sequential evolution of the lateral plate mesoderm.

The origin of paired fins has long been a focus of both paleontologists and developmental biologists. Fossil records indicate that the first pair of fin-like structures emerged in the body wall of early vertebrates. However, extant agnathan lampreys and hagfishes lack paired fins, and thus it has been difficult to determine the developmental processes underlying the ancestral acquisition of paired fins in vertebrates. Fortunately, recent advances in our knowledge of the developmental mechanisms of the lateral plate mesoderm among different taxa have provided clues for understanding the evolutionary origin of vertebrate paired appendages.