The first of these adaptive radiations ocurred 370 million years ago, when the earliest tetrapods modified their fins into legs and emerged onto dry land. By 250 million years ago this process had reversed, and the tetrapod walking limb was once again remodeled into a fin for a return to life in the sea.
Both of these transformations are evidenced in the fossil record, and can be chronologically traced across two major extinctions spanning the Devonian to Carboniferous and Permian to Triassic. Research into these key events will improve our understanding of the functional constraints on structure in vertebrates, as well as how this might be influenced by environment, and also what can be gleaned about diversity turnover relative to large-scale ecosystem change.
Department of Earth Sciences, Uppsala University