The models show the life cycles of a fish and a frog. explain why these life cycles show characteristics common to their class of vertebrates.

This is because all land vertebrates share a common ancestor. All land vertebrates emanated from evolution form the oceans and seas from a group categorized as Sacropterygii. Therefore during the early phylotypic stages of embryonic development, the embryos of all land vertebrates look alike morphologically. It is believed it is during this stage that the basic plan of the body takes shape before it begins to diverge.