Colin Tudge wrote:Mammals are a clade, and therefore the cladists are happy to acknowledge the traditional taxon Mammalia; and birds, too, are a clade, universally ascribed to the formal taxon Aves.
To ni bil edini takratni sistem razvrščanja: v "Hunterian lectures" na Royal College of Surgeons leta 1863, je Huxley združil vretenčarje v sesalce, sauroide in ichthyoide (slednji vsebuje ribe in dvoživke).