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Learn more about "Vertebrate"

Vertebrate

Vertebrates are members of the subphylum '''Vertebrata''', chordates with Vertebra|backbones or Vertebral column|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. Vertebrata is the largest subphylum of chordates, and contains many familiar groups of large land animals. Vertebrates comprise Agnatha|cyclostomes, bony fish, sharks and Batoidea|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 vertebral column|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.

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. According to recent molecular analysis Hagfish|Myxini (hagfish) also belong to Vertebrates. Others consider them a sister group of Vertebrates in the common taxon of Craniata.

Fossil record

The earliest known fossil records of vertebrates are ''Myllokunmingia fengjiaoa'' and ''Haikouichthys ercaicunensis'', from the Chengjiang fauna .

Taxonomy and classification

Classification after Janvier (1981, 1997), Shu ''et al''. (2003), and Benton (2004).
- '''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 amphibian|Amphibia (amphibians)
- ::* Series Amniota (amniotic embryo)
- :::* Class Sauropsida (reptiles and birds)
- ::::* Class bird|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.