page_title: Vertebrate paleontology
section_title: Classification
hierarchical_section_title: Vertebrate paleontology / Classification
caption_attribution_description: English: Evolution of Vertebrate from the Cambrium to the present at a class level as a traditional spindle diagram. The width of the spindle represents the number of families as a rough estimate of diversity. The diagram is based on Benton, M. J. (1998) The quality of the fossil record of vertebrates. P. 269–303, in Donovan, S. K. and Paul, C. R. C. (eds), The adequacy of the fossil record, Fig. 2. Wiley, New York, 312 p. The figures representing classes are (from left): Agnatha, Chondrichthyes, Osteichthyes, Amphibia, Reptilia, Aves and Mammalia. The two extinct classes are Placodermi and Acanthodii. All classes interpreted traditionally. Bentons notes to his own tree: Number of families is an imperfect measure of diversity. Reptilia in particular should probably have been shown as far more diverse in the Mesozoic.
context_page_description: Vertebrate paleontology is the subfield of paleontology that seeks to discover, through the study of fossilized remains, the behavior, reproduction and appearance of extinct animals with vertebrae or a notochord. It also tries to connect, by using the evolutionary timeline, the animals of the past and their modern-day relatives.
  The fossil record shows aspects of the meandering evolutionary path from early aquatic vertebrates to mammals, with a host of transitional fossils, though there are still large blank areas. The earliest known fossil vertebrates were heavily armored fish discovered in rocks from the Ordovician Period about 500 to 430 Ma. The Devonian Period brought in the changes that allowed primitive air-breathing fish to remain on land as long as they wished, thus becoming the first terrestrial vertebrates, the amphibians.
  Amphibians developed forms of reproduction and locomotion and a metabolism better suited for life exclusively on land, becoming more reptilian. Full-fledged reptiles appeared in the Carboniferous Period.
  The reptilian changes and adaptations to diet and geography are chronicled in the fossil record of the varying forms of therapsida.
context_section_description: The "traditional" vertebrate classification scheme employ evolutionary taxonomy where several of the taxa listed are paraphyletic, i.e. have given rise to another taxa that have been given the same rank. For instance, birds are generally considered to be the descendants of reptiles (Saurischian dinosaurs to be precise), but in this system both are listed as separate classes. Under phylogenetic nomenclature, such an arrangement is unacceptable, though it offers excellent overview.
  This classical scheme is still used in works where systematic overview is essential, e.g.  Benton (1998), Hildebrand and Goslow (2001) and Knobill and Neill (2006). While mostly seen in general works, it is also still used in some specialist works like Fortuny & al. (2011).
  Kingdom Animalia
  Phylum Chordata (vertebrates)
  Class Agnatha (jawless fish)
  Subclass Cyclostomata (hagfish and lampreys)
  Subclass Ostracodermi (armoured jawless fish) †
  Class Chondrichthyes (cartilaginous fish)
  Subclass Elasmobranchii (sharks and rayes)
  Subclass Holocephali (chimaeras and extinct relatives)
  Class Placodermi (armoured fish) †
  Class Acanthodii ("spiny sharks", sometimes classified under bony fishes) †
  Class Osteichthyes (bony fish)
  Subclass Actinopterygii
  Subclass Sarcopterygii
  Class Amphibia
  Subclass Labyrinthodontia †
  Subclass Lepospondyli †
  Subclass Lissamphibia
  Class Reptilia
  Subclass Anapsida
  Order Cotylosauria †
  Order Testudines
  Subclass Synapsida
  Order Pelycosauria †
  Order Therapsida †
  Subclass Euryapsida
  Order Sauropterygia †
  Order Ichthyosauria †
  Subclass Diapsida (lizards & snakes too)
  Order Crocodilia (crocodiles, alligators etc.)
  Order Sphenodontia (Tuatara and relatives)
  Order Squamata (Lizards and snakes)
  Order Thecodonts †
  Order Pterosauria †
  Order Saurischia (dinosaurs) †
  Order Ornithischia (dinosaurs) †
  Class Aves
  Subclass Archaeornithes (primitive dinosaur-like birds like Archaeopteryx) †
  Subclass Neornithes (modern birds and some advanced Cretaceous forms)
  Superorder Odontognathae (Cretaceous toothed birds) †
  Superorder Palaeognathae (ratites)
  Superorder Neognathae (All other extant birds)
  Class Mammalia
  Subclass Prototheria
  Order Monotremata (platypus and the echidnas)
  Subclass Theria
  Infraclass Metatheria
  Order Marsupialia (kangaroos, dunnarts, opossums, wombats etc.)
  Infraclass Eutheria (placentals)
  Order Insectivora
  Order Chiroptera (bats)
  Order Creodonta
  Order Carnivora (dogs/cats)
  Order Perissodactyla (horses)
  Order Artiodactyla (cattle and other ungulates)
  Order Proboscidea (elephants)
  Order Edentata
  Order Cetacea (whales and dolphins)
  Order Rodentia (mice, rats etc.)
  Order Lagomorpha (rabbits)
  Order Primates (monkeys, apes and primates)
caption: Classical spindle diagram of the evolution of the vertebrates at class level.
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