Scientists notice structural similarities between fossils of a land animal and an aquatic organism. They know the similarities are not a result of the two organisms having to adapt to similar environments. What can they attribute the structural similarities to?
The answer is common ancestor.
Since these two organisms areĀ adapted to different environments and still have structural similarities, that means that they must have a common ancestor. Common ancestor is an ancestral organism that two or more descendant lineages have in common.