 Both pheneticism and cladism were developed in opposition to entrenched views in systematics. In response, biologists committed to more traditional methods sought to articulate the theoretical underpinnings of their approach, which came to be known as evolutionary systematics. With Ernst Mayr as their most prominent advocate, evolutionary systematists sought to incorporate phylogeny into classifications, but permitted that classifications might also (or even instead) represent important adaptive differences between groups (Simpson 1961; Mayr 1969). A prominent example that regularly featured in these debates is the taxonomic placement of the birds and crocodiles. Mayr argued that though birds are descended from dinosaurs and reptiles more generally, birds share a cluster of adaptations which justify classifying them as a distinctive group at a taxonomically equivalent rank as reptiles. However, even though crocodiles are more closely related to birds than to lizards and thus belong to a clade with birds that lizards are not a part of, Mayr still classifies crocodiles as part of the reptile “grade”—a group characterized by a well integrated adaptive complex (Mayr 1974). Thus unlike the cladists, evolutionary systematists advocated for the inclusion of reptiles and other paraphyletic groups in taxonomy.