Chordates (phylum Chordata) include the vertebrates, together with several closely related invertebrates. They are united by having, at some stage in their life, a hollow dorsal nerve cord (the notochord), pharyngeal slits, a tail extending past the anus, and bands of muscles that go around the body.

The traditional classification of vertebrates contains a wide variety of paraphyletic groups, which in newer systems may either be abandoned or greatly extended. No particular standard system has developed yet, and the groups given at right should be considered tentative.

Other groups that have been used (in alphabetical order):

• Agnatha - jawless vertebrates
• Amniota - reptiles, birds, mammals
• Anapsida - turtles
• Archosauria - crocodiles, birds, dinosaurs, etc.
• Craniata - vertebrates and hagfish
• Diapsida - lepidosaurs and archosaurs
• Dinosauria - dinosaurs, sometimes including birds
• Gnathostomata - jawed vertebrates
• Lepidosauria - lizards and snakes
• Lissamphibia - core amphibians
• Osteichthyes - bony fish, consisting of ray-finned fish and lobe-finned fish, sometimes includes all Tetrapoda
• Sarcopterygii - lobe-finned fish, consisting of coelacanths and lungfish, sometimes includes all Tetrapoda
• Synapsida - mammals and extinct relatives
• Tetrapoda - four-limbed vertebrates\n