Vertebrates represent the majority of the phylum Chordata. Vertebrates are species of animals within the subphylum Vertebrata and include the jawless fish and the jawed vertebrates, which includes the cartilaginous fish (sharks and rays) and the bony fish. Extant vertebrates range in size from some frog species as little as 7.7 millimetres, to the blue whale, at up to 33 metres. Vertebrates make up about 4% of all described animal species, the rest are invertebrates which lack vertebral columns. The defining characteristic of a vertebrate is the vertebral column, in which the notochord (a stiff rod of uniform composition) found in all chordates has been replaced by a segmented series of stiffer elements (vertebrae) separated by mobile joints.

Vertebrates originated about 525 million years ago during the Cambrian Period. Unlike other fauna that dominated the Cambrian, these groups had the basic vertebrate body plan: a notochord, rudimentary vertebrae, and a well-defined head and tail. All of the early vertebrates lacked jaws in the common sense and relied on filter feeding close to the seabed.

The first jawed vertebrates appeared in the late Ordovician and became common in the Devonian, often known as the "Age of Fishes". During this time two groups of bony fishes evolved and became common. The Devonian also saw the demise of virtually all jawless fishes, save for lampreys and hagfish, as well as the Placodermi, a group of armoured fish that dominated much of the late Silurian. The Devonian also saw the rise of the first labyrinthodonts, which was a transitional form between fishes and amphibians.

The Amniotes, a clade of tetrapod vertebrates comprising the reptiles, birds and mammals, branched from labyrinthodonts in the subsequent Carboniferous period. In the sea, the bony fishes became dominant. The birds were derived from a form of dinosaurs and evolved in the Jurassic. The demise of the non-avian dinosaurs at the end of the Cretaceous allowed for expansion of the mammals, which had first evolved during the late Triassic Period.