According to embryology, why do fish and birds have a common ancestor?

Embryology can provide evidence of common ancestry when different animals share features during early development. Fish and birds both have embryos with gill slits and tails, even though these features develop differently or change as they grow. That shared embryonic pattern supports the idea that they have a common ancestor, so the correct choice is “They both have embryos with gill slits and tails.”

AI-written and checked against the verified answer.