Evolutionary Taxonomy

Combining the notions of similarity and descent has been the approach of mainstream evolutionary taxonomists for years.

They classify initially on the basis of true similarity (i.e. not convergent similarity but similarity due to shared phylogeny or evolutionary history) and then test their classifications against the evidence for common descent, including the fossil record.

Therefore, in evolutionary taxonomy (in contrast to cladistics) the crocodiles would be classified with the "true reptiles" because they still retain a reptilian "grade" of organisation, while birds would be the "out-group" despite being more closely related (by common descent) to the true reptiles.