Classification[edit]

Taxonomy[edit]

A skeleton of the blue whale, the world's largest animal, outside the Long Marine Laboratory at the University of California, Santa Cruz

A peregrine falcon, the world's fastest animal

Traditionally, Cephalochordata and Craniata were grouped into the proposed clade "Euchordata", which would have been the sister group to Tunicata/Urochordata. More recently, Cephalochordata has been thought of as a sister group to the "Olfactores", which includes the craniates and tunicates. The matter is not yet settled.

The following schema is from the third edition of Vertebrate Palaeontology.^[37] The invertebrate chordate classes are from Fishes of the World.^[38] While it is structured so as to reflect evolutionary relationships (similar to a cladogram), it also retains the traditional ranks used in Linnaean taxonomy.

• Phylum Chordata
  • Subphylum Tunicata (Urochordata) – (tunicates; 3,000 species)
    • Class Ascidiacea (sea squirts)
    • Class Thaliacea (salps)
    • Class Appendicularia (larvaceans)
    • Class Sorberacea
  • Subphylum Cephalochordata (Acraniata) – (lancelets; 30 species)
    • Class Leptocardii (lancelets)
  • Subphylum Vertebrata (Craniata) (vertebrates – animals with backbones; 57,674 species)
    • Infraphylum incertae sedis (Cyclostomata)
      • Superclass 'Agnatha' paraphyletic (jawless vertebrates; 100+ species)
        • Class Myxini (hagfish; 65 species)
        • Class Petromyzontida or Hyperoartia (lampreys)
        • Class †Conodonta
        • Class †Pteraspidomorphi
        • Class †Thelodonti
        • Class †Anaspida
        • Class †Cephalaspidomorphi
    • Infraphylum Gnathostomata (jawed vertebrates)
      • Superclass incertae sedis
        • Class †Placodermi (Paleozoic armoured forms)
        • Class Chondrichthyes (cartilaginous fish; 900+ species)
        • Class †Acanthodii (Paleozoic "spiny sharks")
      • Superclass Osteichthyes (bony fish; 30,000+ species)
        • Class Actinopterygii (ray-finned fish; about 30,000 species)
        • Class Sarcopterygii (lobe-finned fish: 8 species)
      • Superclass Tetrapoda (four-limbed vertebrates; 28,000+ species) (The classification below follows Benton 2004, and uses a synthesis of rank-based Linnaean taxonomy and also reflects evolutionary relationships. Benton included the Superclass Tetrapoda in the Subclass Sarcopterygii in order to reflect the direct descent of tetrapods from lobe-finned fish, despite the former being assigned a higher taxonomic rank.)^[39]
        • Class Amphibia (amphibians; 7,000 species)
        • Class Sauropsida (reptiles (including birds); 9,000+ species)
        • Class Synapsida (mammals; 5,700+ species)

Phylogeny[edit]

Chordates

Cladogram of the Chordate phylum. Lines show probable evolutionary relationships, including extinct taxa, which are denoted with a dagger, †. Some are invertebrates. The positions (relationships) of the Lancelet, Tunicate, and Craniata clades are as reported[40] in the scientific journal Nature. Note that this cladogram, in showing the extant cyclostomes (hagfish and lamprey) as paraphyletic, is contradicted by nearly all recent molecular data, which support the monophyly of the extant cyclostomes (see Ota and Kurakani 2007 and references therein for a review of evidence).[41] Chordata  Cephalochordata Amphioxus Olfactores †Haikouella Tunicata Appendicularia (formerly Larvacea) Thaliacea Ascidiacea Craniata Myxini Vertebrata †Myllokunmingia fengjiaoa †Zhongjianichthys rostratus Conodonta† Cephalaspidomorphi† Hyperoartia (Petromyzontida)(Lampreys) Pteraspidomorphi† osteostracan† Gnathostomata Placodermi† (?paraphyletic) Chondrichthyes Teleostomi Acanthodii† (?paraphyletic) Osteichthyes Actinopterygii Sarcopterygii void  Tetrapoda   Amphibia  Amniota   Mammalia  Sauropsida  void  Lepidosauromorpha(lizards, snakes,tuatara, and theirextinct relatives)  Archosauromorpha(crocodiles, birds, and their extinct relatives)

                                                                                                                                                

Closest nonchordate relatives[edit]