Vertebrate

Taxobox
name = Vertebrates
fossil_range = Early Cambrian - Recent

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. 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. [cite web |url=http://www.iucn.org/bookstore/HTML-books/Red%20List%202004/completed/table2.1.html | title=A Global Species Assessment | publisher=World Conservation Union |author=Jonathan E.M. Baillie, et al. |year=2004] 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. [cite web |url=http://webs.lander.edu/rsfox/invertebrates/branchiostoma.html |title=Branchiostoma |author=Richard Fox | year=2004]

Evolutionary history

Vertebrates originated about 500 million years ago during the Cambrian explosion, which is part of the Cambrian period. The earliest known vertebrate is Myllokunmingia. [ cite journal|title=Lower Cambrian vertebrates from south China | author=Shu et al. |date=November 4 1999|journal=Nature| volume=402|pages=42–46|doi= 10.1038/46965] 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.cite journal|title=Monophyly of Lampreys and Hagfishes Supported by Nuclear DNA–Coded Genes | author=Kuraku et al. |date=December 1999|journal=Journal of Molecular Evolution doi|10.1007/PL00006595 | volume = 49 | pages = 729|doi=10.1007/PL00006595]

Fossil record

The earliest known fossil records of vertebrates are "Myllokunmingia fengjiaoa" and "Haikouichthys ercaicunensis", dating somewhere between 513–542 mya during the Early Cambrian. The fossils were discovered in Yunnan, China [http://paleodb.org/cgi-bin/bridge.pl] .

Taxonomy and classification

Classification after Janvier (1981, 1997), Shu "et al". (2003), and Benton (2004).cite book | last =Benton | first =Michael J. | authorlink =Michael Benton | title =Vertebrate Palaeontology | publisher =Blackwell Publishing | date= 2004-11-01 |edition=Third Edition | location = | pages =455 pp. | url =http://palaeo.gly.bris.ac.uk/benton/vertclass.html | doi = | id = | isbn =0632056371/978-0632056378]

* Subphylum Vertebrata
** (Unranked group) Hyperoartia (lampreys)
** Class †Conodonta
** Subclass †Pteraspidomorphi
** Class †Thelodonti
** Class †Anaspida
** Class †Galeaspida
** Class †Pituriaspida
** Class †Osteostraci
** Infraphylum Gnathostomata (jawed vertebrates):::* Class †Placodermi (Paleozoic armoured forms):::* Class Chondrichthyes (cartilaginous fish):::* Class †Acanthodii (Paleozoic "spiny sharks")::* Superclass Osteichthyes (bony fish):::* Class Actinopterygii (ray-finned fish):::* Class Sarcopterygii (lobe-finned fish)::::* Subclass Coelacanthimorpha (coelacanths)::::* Subclass Dipnoi (lungfish)::::* Subclass Tetrapodomorpha (ancestral to tetrapods)::* Superclass Tetrapoda (four-limbed vertebrates)::::* Class Amphibia (amphibians):::* Series Amniota (amniotic embryo)::::* Class Sauropsida (reptiles and birds):::::* Class Aves (birds)::::* Class Synapsida (mammal-like reptiles):::::* Class Mammalia (mammals)

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. [cite web | title=vertebra |publisher=Dictionary.com. |work=Online Etymology Dictionary |author=Douglas Harper, Historian |url=http://dictionary.reference.com/browse/vertebra]

References

Bibliography

See also

* Invertebrate
* Marine vertebrates

External links

* [http://tolweb.org/Vertebrata/14829 Tree of Life]
* [http://www.nature.com/nature/journal/v439/n7079/abs/nature04336.html Tunicates and not cephalochordates are the closest living relatives of vertebrates]
* [http://vector.ifas.ufl.edu/chapter_07.htm Vertebrate Pests] chapter in EPA and UF / IFAS National Public Health Pesticide Applicator Training Manual