Fur seals and sea lions have similar body shapes and features. based on their anatomy, they seem to have a relatively recent common evolutionary ancestor. what further evidence would best substantiate that the two animals have a recent common ancestor?

Looking at the two species' DNA would be a good place to start. If there are a number of similarities in their genotypes, then there would be a good chance that the two would also share some type of a common ancestor. This would be evidence that there was some type of selection that took place that necessitated two different species that shared a number of traits and features.