Chordata

Classification

The traditional classification of vertebrates is a mess, with a wide variety of paraphyletic groups that have either been abandoned or extended (here marked B). Unfortunately, no particularly standard system has settled in to replace it; the problem is there have been too many adaptive radiations. For now, here is a minimal tree of living forms including most traditionally class-sized groups:

:Urochordata

:Cephalochordata

:Craniata

::Myxini (hagfish)

::Vertebrata

:::Petromyzontiformes (lampreys)

:::Gnathostoma

::::Chondrichthyes (cartiligenous fish)

::::Osteichthyes B

:::::Actinopterygii (ray-finned fish)

:::::Sarcopterygii B

::::::Coelocanthamorpha

::::::Dipnoi (lungfish)

::::::Tetrapoda

:::::::Lissamphibia (frogs, toads, salamanders)

:::::::Amniota

::::::::Mammalia

::::::::Chelonia (turtles)

::::::::Squamata (lizards, snakes)

::::::::Sphenodontida (tuataras)

::::::::Crocodylomorpha (crocodiles, alligators)

::::::::Aves (birds)

Information on characteristics of each group and a more detailed classification thereof should probably go under its headline - eg details of skeletal system and listing of jawless fishes under Vertebrata.

Subphylum Urochordata

Class Ascidiacea

Subphylum Cephalochordata

Subphylum Vertebrata

Superclass Agnatha ("Without jaws")

Superclass Gnathostomata ("Jawed mouth")

Class Chondrichthyes (cartilaginous fishes)

Class Osteichthyes (bony fishes)

Class Amphibia (amphibians)

Class Reptilia (reptiles)

Class Aves (birds)

Class Mammalia (mammals)