The Origin and Mechanisms of Development of Paired Fins in Vertebrates

The emergence of paired appendages is one of the most important adaptations of vertebrates; it provided the opportunity to lead an active lifestyle and develop a wide range of ecological niches. Fish fins are a basic form of paired appendages in evolution. The problem of the emergence of paired appendages has attracted the attention of researchers for more than 150 years. During this time, a number of theories have been proposed, based primarily on morphological data, two of which, the Balfour–Thatcher–Mivart lateral fold theory and the Gegenbaur gill arch theory, have not lost their relevance. However, to date, none of the proposed ideas has decisive evidence in its favor. In recent years, new data have been obtained in favor of each of the theories, which emphasize the search for options for their consistent synthesis. In this review article, we attempt to consider the results and analyze the hypotheses regarding the prerequisites and mechanisms that led to the emergence of paired appendages in vertebrates.