   #copyright

Vertebrate

2007 Schools Wikipedia Selection. Related subjects: General Biology

   iVertebrates

                 Fossil range: mid Early Cambrian to Recent

   Northern bluefin tuna, Thunnus thynnus
   Northern bluefin tuna, Thunnus thynnus
                  Scientific classification

   Kingdom:   Animalia
   Phylum:    Chordata
   (unranked) Craniata
   Subphylum: Vertebrata

              Cuvier, 1812

                             Classes and Clades

   See below

   Vertebrates are members of the subphylum Vertebrata (within the phylum
   Chordata), specifically, those chordates with backbones or spinal
   columns. About 57,739 species of vertebrates have been described.
   Vertebrates started to evolve about 530 million years ago during the
   Cambrian explosion, which is part of the Cambrian period (first known
   vertebrate is Myllokunmingia). Their name derives from the bones of the
   spinal column (or vertebral column), the vertebrae. Vertebrata is the
   largest subphylum of chordates, and contains many familiar groups of
   large land animals. Fish (including lampreys, but traditionally not
   hagfish, though this is now disputed), amphibians, reptiles, birds, and
   mammals (including humans) are vertebrates. Characteristics of the
   subphylum are a muscular system that mostly consists of paired masses,
   as well as a central nervous system which is partly located inside the
   backbone (if one is present). Usually, the defining characteristic of a
   vertebrate is considered the backbone or spinal cord, a brain case, and
   an internal skeleton, but the former do not hold true for lampreys, and
   the latter is arguably present in some other chordates. Rather, all
   vertebrates are most easily distinguished from all other chordates by
   having an unequivocal 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 no true
   head, and "see" with their entire back.

Anatomy

   The internal skeleton which defines vertebrates consists of cartilage
   or bone, or in some cases both. An outer skeleton in form of a bony
   armour was the first bony substance the vertebrates evolved. It is
   possible its primary function was as a phosphate reservoir, excreted as
   calcium phosphate and stored around the body, offering protection at
   the same time. The skeleton provides support to the organism during the
   period of growth. For this reason vertebrates can achieve larger sizes
   than invertebrates, and on average vertebrates are in fact larger. The
   skeleton of most vertebrates, that is excluding the most primitive
   ones, consists of a skull, the vertebral column and two pairs of limbs.
   In some forms of vertebrates, one or both of these pairs of limbs may
   be absent, such as in snakes or whales. These limbs have been lost in
   the course of evolution.

   The skull is thought to have facilitated the development of
   intelligence as it protects vital organs such as the brain, the eyes
   and the ears. The protection of these organs is also thought to have
   positively influenced the development of high responsiveness to the
   environment often found in vertebrates.

   Both the vertebral column and the limbs support the body of the
   vertebrate overall. This support facilitates movement. Movement is
   normally achieved with muscles that are attached directly to the bones
   or cartilages. The contour of the body of a vertebrate is formed by the
   muscles. A skin covers the inner parts of a vertebrate's body. The skin
   sometimes acts as a structure for protective features, such as horny
   scales or fur. Feathers may also be attached to the skin.

   The trunk of a vertebrate is hollow and houses the internal organs. The
   heart and the respiratory organs are protected in the trunk. The heart
   is located behind the gills, or where there are lungs, in between the
   lungs.

   The central nervous system of a vertebrate consists of the brain and
   the spinal cord. Both of these are characterized by being hollow. In
   lower vertebrates the brain mostly controls the functioning of the
   sense organs. In higher vertebrates the size of the brain relative to
   the size of the body is greater. This larger brain enables more
   intensive exchange of information between the different parts of the
   brain. The nerves from the spinal cord, which lies behind the brain,
   extend to the skin, the inner organs and the muscles. Some nerves are
   directly connected to the brain, linking the brain with the ears and
   lungs.

Evolution

   Vertebrates have been traced back to Myllokunmingia during the Cambrian
   explosion (530 million years ago), the ostracoderms of the Silurian
   Period (444 million to 409 million years ago), and the conodonts, a
   group of eel-like vertebrates characterized by multiple pairs of bony
   toothplates.

Taxonomy

   Classification after Janvier (1981, 1997), Shu et al. (2003), and
   Benton (2004) .
     * Subphylum Vertebrata
          + (Unranked group) Hyperoartia ( lampreys)
          + Class † Conodonta
          + Class † Pteraspidomorphi
          + Order † Thelodonti
          + Order † Anaspida
          + Order † Galeaspida
          + Order † Pituriaspida
          + Order † Osteostraci
          + Infraphylum Gnathostomata (jawed vertebrates)

                    # Class † Placodermi (Paleozoic armoured forms)
                    # Class Chondrichthyes (cartilaginous fish)
                    # Class † Acanthodii (Paleozoic "spiny sharks")

               o 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)

               o 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)

   Retrieved from " http://en.wikipedia.org/wiki/Vertebrate"
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   with only minor checks and changes (see www.wikipedia.org for details
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