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.