Chordate

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{{Taxobox | color = pink | name = Chordates | image = Tuna.jpg | image_caption = Yellowfin tuna, Thunnus albacares | regnum = Animalia | superphylum = Deuterostomia | phylum = Chordata | phylum_authority = Bateson, 1885 | subdivision_ranks = Typical Classes | subdivision =

• Subphylum Urochordata - Tunicatas
  • Ascidiacea
  • Thaliacea
  • Larvacea
• Subphylum Cephalochordata - Lancelets
• Subphylum Myxini - Hagfishes
• Subphylum Vertebrata - Vertebrates
  • Cephalaspidomorphi - Lampreys
  • Placodermi (extinct)
  • Chondrichthyes - Cartilaginous fishes
  • Acanthodii (extinct)
  • Actinopterygii - Ray-finned fishes
  • Sarcopterygii - Lobe-finned fishes
  • Amphibia - Amphibians
  • Sauropsida - Reptiles
  • Synapsida - Mammal-like reptiles
  • Aves - Birds
  • Mammalia - Mammals

}} Chordates (phylum Chordata) are a group of animals that includes the vertebrates, together with several closely related invertebrates. They are united by having, at some stage in their life, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a muscular tail extending past the anus. Some scientists argue, however, that the true qualifier should be pharyngeal pouches rather than slits.

The phylum Chordata is broken down into three subphyla: Urochordata, Cephalochordata, and Vertebrata. Urochordate larvae have a notochord and a nerve cord but they are lost in adulthood. Cephalochordates have a notochord and a nerve cord but no vertebra. In all vertebrates except for Hagfish, the dorsal hollow nerve cord has been surrounded with cartilaginous or bony vertebrae and the notocord generally reduced.

The chordates and two sister phyla, the hemichordates and the echinoderms, make up the deuterostomes, a superphylum.

It has been theorised that the phylum originated as a result of paedomorphy occurring in a primitive animal, like a sponge or coral.

The extant groups of chordates are related as shown in the phylogenetic tree, below. They do not match up very well with the traditional groups, and as a result vertebrate classification is in a state of flux, although their relationships are not very well understood.

Phylum Chordata

• Subphylum Urochordata
• Subphylum Cephalochordata
• Craniata (animals with skulls)
  • Subphylum Myxini or Hyperotreti (hagfish)
  • Subphylum Vertebrata (animals with backbones)
    • Class Cephalaspidomorphi (lampreys)
    • Gnathostomata (jawed vertebrates)
      • Class Chondrichthyes (cartilaginous fish)
      • Teleostomi (bony fish, ~ Osteichthyes)
        • Class Acanthodii
        • Class Actinopterygii (ray-finned fish)
        • Class Sarcopterygii (lobe-finned fish)
          • Superclass Tetrapoda (four-legged vertebrates)
            • Class Amphibia (amphibians)
            • Amniota (amniotic egg)
              • Class Synapsida (mammal-like reptiles)
                • Class Mammalia (mammals)
              • Class Sauropsida (most modern reptiles)
                • Subclass Anapsida
                  • Order Testudines (turtles)
                • Subclass Diapsida
                  • Order Lepidosauria (lizards, snakes, tuatara)
                  • Archosauria
                    • Order Crocodilia (crocodiles, alligators, caimans, gharials)
                    • Superorder Dinosauria
                      • Class Aves (birds)

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