 Around the same time, another group (phylogenetic systematists) insisted that recency of common ancestry provided the best theoretically-motivated foundation for relatedness (Hennig 1966). Like the pheneticists, they too sought to promote good scientific methods in systematics, and were similarly critical of established approaches. The phylogenetic systematists can be characterized by their insistence that all taxonomic groups above the species level should be monophyletic. Thus, if birds are descended from dinosaurs then they are dinosaurs (Padian &amp; Horner 2002). If the dinosaurs (or the reptiles more generally) are defined in a way that excludes birds, then the group is paraphyletic and thus cannot be a taxon in a phylogenetic taxonomic system. Ernst Mayr derisively named them “cladists” for their obsessive focus on recovering clades (i.e., monophyletic groups) (Mayr 1965a), though its practitioners were happy to embrace the name. When consistently carried out, phylogenetic taxonomic principles led to major revisions in long-standing, traditional classifications—revisions that often generated deep controversy (e.g., Halstead 1978; Gardiner et al. 1979).