On some principles of taxonomy

In eukaryotes, in contrast to prokaryotes, phyletic lineages are usually quite distinct. Therefore, the best classifications of eukaryotes are usually phylogeny-based. However, in many groups of organisms, higher rank taxa are based on horizontal rather than phyletic groups or, more precisely, on groups of the mixed type. This is largely true for vertebrates where the division into fishes and tetrapods or into anamniotes (nonamniotes) and amniotes is just of the mixed type. Frequent parallelisms in these cases make the strict adherence to the principle of monophyly senseless and imply a compromise system. Strict cladistic practice violates this approach and ignores Hennig’s rule that his methodology should only be applied to synchronous organisms.