Vertebrate
Vertebrata is a subphylum of
chordates, specifically, those 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 . Their name derives from the bones of the spinal column , the
vertebrae.
Vertebrata is the largest subphylum of chordates, and contains most animals with which people are generally familiar .
Fish ,
amphibians,
reptiles,
birds, and mammals are vertebrates.
Encyclopedia
Vertebrata is a subphylum of
chordates, specifically, those 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 . Their name derives from the bones of the spinal column , the
vertebrae.
Vertebrata is the largest subphylum of chordates, and contains most animals with which people are generally familiar .
Fish ,
amphibians,
reptiles,
birds, and mammals 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 . 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 , the ostracoderms of the Silurian Period , and the
conodonts, a group of eel-like vertebrates characterized by multiple pairs of bony toothplates.
Taxonomy
Classification after Janvier , Shu
et al. , and Benton .
...
- Class †Pteraspidomorphi
- Order †Thelodonti
- Order †Anaspida
- Order †Galeaspida
- Order †Pituriaspida
- Order †Osteostraci
- Infraphylum Gnathostomata
...
See also
External links
