Wikipedia:Vertebrate
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| Vertebrates Fossil range: 525–0 Ma Ordovician - Recent |
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 Fossilized skeleton of Diplodocus, showing an extreme example of the backbone that characterizes the vertebrates
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Vertebrates are members of the subphylum Vertebrata, chordates with backbones or spinal columns. About 58,000 species of vertebrates have been described.[1] 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). Vertebrates make up about 5% of all described animal species; the rest are invertebrates which lack backbones.
The grouping sometimes includes the hagfish, which have no vertebrae, but are genetically quite closely related to lampreys, which do have vertebrae.[2] For this reason, the sub-phylum is sometimes referred to as "Craniata", as all members do possess a cranium.
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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.[3]
Anatomy and morphology
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All vertebrates are built along the basic Chordate body plan: A stiff rod (the vertebral column) is running through the length of the animal, with a hollow tube of nervous tissue (the spinal cord) above it and the gastrointestinal tract below. In all vertebrates the mouth is found at or right below the anterior end of the animal, while the anus opens to the exterior before the end of the body. The remaining part of the body continuing aft of the anus form a tail with vertebrae and spinal cord, but no gut.
The defining characteristic of a vertebrate is considered to be 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.[4] Vertebrates are also known for obtaining two pairs of appendages, but within certain species no limbs are presented. Abnormally, certain species of vertebrates may also develop extra pairs of limbs upon their bodies. These are results of mutuation and possible infections of parasitic organisms.
One characteristic of the subphylum is 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).
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.[5] According to recent molecular analysis Myxini (hagfish) also belong to Vertebrata. Others consider them a sister group of vertebrates in the common taxon of Craniata.[2] Another early vertebrate is Haikouichthys ercaicunensis, also from the Chengjiang fauna . All of these groups lacked a jaw in the common sense.
Jawed vertebrates appeared in the Ordovician, and became common in the Devonian, the "Age of Fishes". The Devonian also saw the demise of much of the early jawless forms as well as the rise of the first labyrinthodonts, transitional between fish and amphibians.
The reptiles appeared in the subsequent Carboniferous period. The anapsid and synapsid reptiles where common during the late Paleozoic, while the diapsids became dominant during the Mesozoic. The dinosaurs gave rise to the birds in the Jurassic. The demise of the dinosaurs at the end of the Cretaceous promoted expansion of the mammals, which had developed from the synapsid reptiles during the Late Triassic Period.
Taxonomy and classification
There are several ways of classing animals. Evolutionary systematics relies on anatomy, physiology and evolutionary history. Phylogenetic classification is based solely on phylogeny. Evolutionary systematics give an overview; phylogenetic systematics gives detail. The two systems are thus complementary rather than opposed.[6]
Formal classification
Traditional classification has the vertebrates grouped into seven classes based on gross anatomical and physiological traits. This classification is the one most commonly encountered in school textbooks, overviews, non-specialist and popular works. [7]
- Class Agnatha (jawless fish)
- Class Chondrichthyes (cartilaginous fish)
- Class Osteichthyes (bony fish)
- Class Amphibia (amphibians)
- Class Reptilia (reptiles)
- Class Aves (birds)
- Class Mammalia (mammals)
Most of the classes listed are not "complete" taxons: the agnathans have given rise to the jawed vertebrates; the cartilaginous fishes have given rise to the bony fishes, which in 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
While the above classification is orderly, it has come under critique from cladistics, as most of the groups are paraphyletic, i.e. have given rise to other groups. 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)[8] is given here:
- Subphylum Vertebrata
- (Unranked group) Hyperoartia (lampreys)
- Class †Conodonta
- Class †Pteraspidomorphi
- Class †Thelodonti
- Class †Anaspida
- Class †Galeaspida
- Class †Pituriaspida
- Class †Osteostraci
- Infraphylum Gnathostomata (jawed vertebrates)
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- Class †Placodermi (Paleozoic armoured forms)
- Class Chondrichthyes (cartilaginous fish)
- Class †Acanthodii (Paleozoic "spiny sharks")
- Superclass Osteichthyes (bony fish)
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- Class Actinopterygii (ray-finned fish)
- Class Sarcopterygii (lobe-finned fish)
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- Subclass Coelacanthimorpha (coelacanths)
- Subclass Dipnoi (lungfish)
- Subclass Tetrapodomorpha (ancestral to tetrapods)
- Superclass Tetrapoda (four-limbed vertebrates)
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See also
References
- ^ Jonathan E.M. Baillie, et al. (2004). "A Global Species Assessment". World Conservation Union. http://www.iucn.org/bookstore/HTML-books/Red%20List%202004/completed/table2.1.html.
- ^ 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:.
- ^ Douglas Harper, Historian. "vertebra". Online Etymology Dictionary. Dictionary.com.. http://dictionary.reference.com/browse/vertebra.
- ^ Richard Fox (2004). "Branchiostoma". http://webs.lander.edu/rsfox/invertebrates/branchiostoma.html.
- ^ Shu et al. (November 4, 1999). "Lower Cambrian vertebrates from south China". Nature 402: 42–46. doi:.
- ^ 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
- ^ Romer, A.S. (1949): The Vertebrate Body. W.B. Saunders, Philadelphia. (2nd ed. 1955; 3rd ed. 1962; 4th ed. 1970)
- ^ Benton, Michael J. (2004-11-01). Vertebrate Palaeontology (Third ed.). Blackwell Publishing. pp. 455 pp.. ISBN 0632056371/978-0632056378. http://palaeo.gly.bris.ac.uk/benton/vertclass.html.
Bibliography
- Kardong, Kenneth V. (1998). Vertebrates: Comparative Anatomy, Function, Evolution (second ed.). USA: McGraw-Hill. pp. 747 pp.. ISBN 0-07-115356-X/0-697-28654-1. http://www.amazon.com/Vertebrates-Comparative-Anatomy-Function-Evolution/dp/0072909560.
- Vertebrata (TSN 331030). Integrated Taxonomic Information System. Retrieved on 6 August 2007.
External links
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Wikispecies has information related to: Vertebrata |
- Tree of Life
- Tunicates and not cephalochordates are the closest living relatives of vertebrates
- Vertebrate Pests chapter in United States Environmental Protection Agency and University of Florida/Institute of Food and Agricultural Sciences National Public Health Pesticide Applicator Training Manual
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