Taxonomy and phylogeny

Subphylum Vertebrata
└─Infraphylum Gnathostomata
├─Class Placodermi

Placodermi

Placodermi is a class of armoured prehistoric fish, known from fossils, which lived from the late Silurian to the end of the Devonian Period. Their head and thorax were covered by articulated armoured plates and the rest of the body was scaled or naked, depending on the species. Placoderms were...

 — extinct (armored gnathostomes)
└Microphylum Eugnathostomata (true jawed vertebrates)
├─Class Chondrichthyes

Chondrichthyes

Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nares, scales, two-chambered hearts, and skeletons made of cartilage rather than bone...

 (cartilaginous fish)
└─(unranked) Teleostomi

Teleostomi

Teleostomi is a clade of jawed vertebrates that includes the tetrapods, bony fish, and the wholly extinct acanthodian fish. Key characters of this group include an operculum and a single pair of respiratory openings, features which were lost or modified in some later representatives...

 (Acanthodii & Osteichthyes)
├─Class Acanthodii

Acanthodii

Acanthodii is a class of extinct fishes, sharing features with both bony fish and cartilaginous fish. In form they resembled sharks, but their epidermis was covered with tiny rhomboid platelets like the scales of holosteans...

 — extinct ("spiny sharks")
└Superclass Osteichthyes

Osteichthyes

Osteichthyes , also called bony fish, are a taxonomic group of fish that have bony, as opposed to cartilaginous, skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of over 29,000 species...

 (bony fish)
├─Class Actinopterygii

Actinopterygii

The Actinopterygii or ray-finned fishes constitute a class or sub-class of the bony fishes.The ray-finned fishes are so called because they possess lepidotrichia or "fin rays", their fins being webs of skin supported by bony or horny spines , as opposed to the fleshy, lobed fins that characterize...

 (ray-finned fish)
└─Class Sarcopterygii

Sarcopterygii

The Sarcopterygii or lobe-finned fishes – sometimes considered synonymous with Crossopterygii constitute a clade of the bony fishes, though a strict classification would include the terrestrial vertebrates...

 (lobe-finned fish)
└Superclass Tetrapoda
├─Class Amphibia (amphibians)
└(unranked) Amniota (amniotic egg)
├─Class Sauropsida

Reptile

Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

 (reptiles or sauropsids)
│ └─Class Aves

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

 (birds)
└─Class Synapsida
└─Class Mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

ia (mammals)
 
Note: lines show evolutionary relationships.