An evidence of a common ancestral for fishes, amphibians, reptiles, birds and mammals is the

The evidence of a common ancestor for fishes, amphibians, reptiles, birds and mammals is the presence of gill clefts in vertebrate embryos. All vertebrate embryos at some point during development have gill slits, which are openings in the neck region that eventually develop into various structures in different species. This is evidence of a shared ancestry because it indicates that these organisms share a common developmental pathway that has been modified over time through evolution to produce the diverse range of adult forms seen in these groups. Possession of wings by birds and bats, cold-bloodedness of fishes, amphibians, and reptiles, and possession of scales by fish and reptiles are all characteristics that have evolved independently in these groups and are not unique to their common ancestor.