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Vertebrate

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Vertebrates
Temporal range: 530–0 Ma Early Cambrian - Recent
Blotched Blue-tongued Lizard, Tiliqua nigrolutea
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata Template:Taxobox norank entry
Subphylum:
Vertebrata

Cuvier, 1812
Groups

Vertebrates are members of the subphylum Vertebrata, chordates with backbones or spinal columns. The grouping sometimes includes the hagfish, which have no vertebrae, but are genetically quite closely related to lampreys, which do have vertebrae.[1] For this reason, the sub-phylum is sometimes referred to as "Craniata", as all members do possess a cranium. About 58,000 species of vertebrates have been described.[2] Vertebrata is the largest subphylum of chordates, and contains many familiar groups of large land animals. Vertebrates comprise cyclostomes, bony fish, sharks and rays, amphibians, reptiles, mammals, and birds. Extant vertebrates range in size from the carp species Paedocypris, at as little as 7.9 mm (0.3 inch), to the Blue Whale, at up to 33 m (110 ft).

Anatomy and morphology

One characteristic of the subphylum are that all members have muscular systems that mostly consist of paired masses, as well as a central nervous system which is partly located inside the backbone (if one is present). The defining characteristic of a vertebrate is considered the backbone or spinal cord, a brain case, and an internal skeleton, but the latter do not hold true for lampreys, and the former is arguably present in some other chordates. Rather, all vertebrates are most easily distinguished from all other chordates by having a clearly identifiable head, that is, sensory organs – especially eyes are concentrated at the fore end of the body and there is pronounced cephalization. Compare the lancelets which have a mouth but not a well-developed head, and have light-sensitive areas along their entire back.[3]

Evolutionary history

Vertebrates originated about 525 million years ago during the Cambrian explosion, which is part of the Cambrian period. The earliest known vertebrate is Myllokunmingia.[4] According to recent molecular analysis Myxini (hagfish) also belong to Vertebrates. Others consider them a sister group of Vertebrates in the common taxon of Craniata.[1] Another early vertebrate is Haikouichthys ercaicunensis, also from the Chengjiang fauna 518 million years ago.

Taxonomy and classification

There are several ways of classing animals. Traditinal systematics or evolutionary systematics rely on anatomy, physiology and evolutionary history. Phylogenetic classification is based soley on phylogeny. Traditional systematics give overview, phylogenetig systematics give detail. The two systems are thus complimentary rather than opposed. [5]

Formal classification

Traditional classification has the vertebrates classed into seven classes based on gross anatomical and physiological traits: [6]

This classification is the one most commonly encountered in school textbooks and popular works. While orderly and easy to use, has come under critique from cladistics, as most of the groups are paraphyletic, i.e. have given rise to other groups: The Agnathans have given rise to the jawed vertebrates, the cartilaginous fishes have given rise to the bony fishes, who in their turn have given rise to the land vertebrates. On land the amphibians gave rise to the reptiles and the reptiles to both birds and mammals.

Phylogenetic classification

Quite a few authors working in the field use a classification based on purely on phylogeny, disregarding the anatomy and physiology. An example based on Janvier (1981, 1997), Shu et al. (2003), and Benton (2004).[7] is given here:

  • Superclass Tetrapoda (four-limbed vertebrates)

Etymology

The word vertebrate derives from Latin vertebrātus (Pliny), meaning having joints. It is closely related to the word vertebra, which refers to any of the bones or segments of the spinal column.[8]

References

  1. ^ a b Kuraku; et al. (December 1999). "Monophyly of Lampreys and Hagfishes Supported by Nuclear DNA–Coded Genes". Journal of Molecular Evolution doi:10.1007/PL00006595. 49: 729. doi:10.1007/PL00006595. {{cite journal}}: Explicit use of et al. in: |author= (help); External link in |journal= (help); templatestyles stripmarker in |journal= at position 32 (help)
  2. ^ Jonathan E.M. Baillie; et al. (2004). "A Global Species Assessment". World Conservation Union. {{cite web}}: Explicit use of et al. in: |author= (help)
  3. ^ Richard Fox (2004). "Branchiostoma".
  4. ^ Shu; et al. (November 4 1999). "Lower Cambrian vertebrates from south China". Nature. 402: 42–46. doi:10.1038/46965. {{cite journal}}: Check date values in: |date= (help); Explicit use of et al. in: |author= (help)
  5. ^ Hildebran, M. & Gonslow, G. (2001): Analysis of Vertebrate Structure. 5th edition. John Wiley & Sons, Inc. New York, page 33: Comment: The problem of naming sister groups
  6. ^ Romer, A.S. (1949): The Vertebrate Body. W.B. Saunders, Philadelphia. (2nd ed. 1955; 3rd ed. 1962; 4th ed. 1970)
  7. ^ Benton, Michael J. (2004-11-01). Vertebrate Palaeontology (Third Edition ed.). Blackwell Publishing. pp. 455 pp. ISBN 0632056371/978-0632056378. {{cite book}}: |edition= has extra text (help); Check |isbn= value: invalid character (help)
  8. ^ Douglas Harper, Historian. "vertebra". Online Etymology Dictionary. Dictionary.com.

Bibliography

See also

Wikispecies has information related to Vertebrata.
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