Vertebrate

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For an explanation of similar terms, see Craniate.

Vertebrate
Temporal range:
Ma[1]
Vertebrata 002.png
Example of vertebrates:
Tetrapoda), a Tiger shark (Chondrichthyes) and a River lamprey (Agnatha
).
Scientific classification e
Kingdom: Animalia
Superphylum: Deuterostomia
Phylum: Chordata
Clade: Olfactores
Subphylum: Vertebrata
J-B. Lamarck, 1801[2]
Infraphyla
Synonyms

Ossea Batsch, 1788[2]

Vertebrates (

Chordata, with currently about 69,963 species described.[5]
Vertebrates comprise such groups as the following:

invertebrates, which lack vertebral columns
.

The vertebrates traditionally include the

monophyletic sense. Others consider them a sister group of vertebrates in the common taxon of craniata.[9]

Etymology

The word vertebrate derives from the Latin word vertebratus (Pliny), meaning joint of the spine.[10]

Vertebrate is derived from the word

spinal column.[11]

Anatomy and morphology

See also:
Vertebrate anatomy

All vertebrates are built along the basic chordate

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 after the anus forms a tail with vertebrae and spinal cord, but no gut.[13]

Vertebral column

The defining characteristic of a vertebrate is the

chordates
has been replaced by a segmented series of stiffer elements (vertebrae) separated by mobile joints (intervertebral discs, derived embryonically and evolutionarily from the notochord).

However, a few vertebrates have secondarily lost this anatomy, retaining the notochord into adulthood, such as the sturgeon[14] and coelacanth. Jawed vertebrates are typified by paired appendages (fins or legs, which may be secondarily lost), but this trait is not required in order for an animal to be a vertebrate.

Diplodocus carnegii, showing an extreme example of the backbone
that characterizes the vertebrates.

Gills

Gill arches bearing gills in a pike

All

chordate relatives have more than 50 pairs of gills.[13]

In

fishes, the larvae bear external gills, branching off from the gill arches.[16] These are reduced in adulthood, their function taken over by the gills proper in fishes and by lungs in most amphibians. Some amphibians retain the external larval gills in adulthood, the complex internal gill system as seen in fish apparently being irrevocably lost very early in the evolution of tetrapods.[17]

While the more derived vertebrates lack gills, the gill arches form during

thyroid gland, the larynx, the columella (corresponding to the stapes in mammals) and, in mammals, the malleus and incus.[13]

Central nervous system

The central nervous system of vertebrates is based on a hollow nerve cord running along the length of the animal. Of particular importance and unique to vertebrates is the presence of neural crest cells. These are progenitors of stem cells, and critical to coordinating the functions of cellular components.[18] Neural crest cells migrate through the body from the nerve cord during development, and initiate the formation of neural ganglia and structures such as the jaws and skull.[19][20][21]

The vertebrates are the only

organs comparable to those of vertebrates. Other chordates do not show any trends towards cephalisation.[13]

A

rhombencephalon (hindbrain), further differentiated in the various vertebrate groups.[22] Two laterally placed eyes form around outgrowths from the midbrain, except in hagfish, though this may be a secondary loss.[23][24] The forebrain is well-developed and subdivided in most tetrapods, while the midbrain dominates in many fish and some salamanders. Vesicles of the forebrain are usually paired, giving rise to hemispheres like the cerebral hemispheres in mammals.[22]

The resulting anatomy of the central nervous system, with a single hollow nerve cord topped by a series of (often paired) vesicles, is unique to vertebrates. All

brain stem running on each side of the mouth or gut.[13]

Molecular signatures

In addition to the morphological characteristics used to define vertebrates (i.e. the presence of a notochord, the development of a vertebral column from the notochord, a dorsal nerve cord, pharyngeal gills, a post-anal tail, etc.), molecular markers known as

metazoan.[25]
The CSIs in these protein sequences are predicted to have important functionality in vertebrates.

A specific relationship between Vertebrates and

Rrp44 (associated with exosome complex) and serine palmitoyltransferase, that are exclusively shared by species from these two subphyla but not Cephalochordates, indicating Vertebrates are more closely related to Tunicates than Cephalochordates.[25]

Evolutionary history

See also: Evolution of fish and Evolution of tetrapods

External relationships

Originally, the "Notochordata hypothesis" suggested that the

chordates, they all share the presence of a notochord
, at least during a stage of their life cycle.

The following cladogram summarizes the systematic relationships between the Olfactores (vertebrates and tunicates) and the Cephalochordata.

 
Chordata
 
Olfactores
 
Craniata
 

 Vertebrata 

Haikouichthys4.png

 

larvaceans) Salpa scheme.png

 
Cephalochordata
 

 

Amphioxiformes (lancelets) Branchiostoma lanceolatum (Amphioxus lanceolatus).png

First vertebrates

The early vertebrate Haikouichthys

Vertebrates originated during the

Chengjiang biota[29] and lived about 518 million years ago.[1] These include Haikouichthys, Myllokunmingia,[29] Zhongjianichthys,[30] and probably Haikouella.[31] Unlike the other fauna that dominated the Cambrian, these groups had the basic vertebrate body plan: a notochord, rudimentary vertebrae, and a well-defined head and tail.[32] All of these early vertebrates lacked jaws in the common sense and relied on filter feeding close to the seabed.[33][page needed] A vertebrate group of uncertain phylogeny, small eel-like conodonts, are known from microfossils of their paired tooth segments from the late Cambrian to the end of the Triassic.[34]

From fish to amphibians

Acanthostega, a fish-like early labyrinthodont
.

The first

tetrapods in the succeeding Carboniferous
.

Mesozoic vertebrates

birds, both in the Jurassic.[37] After all dinosaurs except birds went extinct by the end of the Cretaceous
, birds and mammals diversified and filled their niches.

After the Mesozoic

The Cenozoic world has seen great diversification of bony fishes, amphibians, reptiles, birds and mammals.

Over half of all living vertebrate species (about 32,000 species) are fish (non-tetrapod craniates), a diverse set of lineages that inhabit all the world's aquatic ecosystems, from snow minnows (Cypriniformes) in Himalayan lakes at elevations over 4,600 metres (15,100 feet) to flatfishes (order Pleuronectiformes) in the Challenger Deep, the deepest ocean trench at about 11,000 metres (36,000 feet). Fishes of myriad varieties are the main predators in most of the world's water bodies, both freshwater and marine. The rest of the vertebrate species are tetrapods, a single lineage that includes amphibians (with roughly 7,000 species); mammals (with approximately 5,500 species); and reptiles and birds (with about 20,000 species divided evenly between the two classes). Tetrapods comprise the dominant megafauna of most terrestrial environments and also include many partially or fully aquatic groups (e.g., sea

penguins
, cetaceans).

Classification

There are several ways of classifying animals.

phylogeny.[38] Evolutionary systematics gives an overview; phylogenetic systematics gives detail. The two systems are thus complementary rather than opposed.[39]

Traditional classification

Traditional spindle diagram of the evolution of the vertebrates at class level

Conventional classification has living vertebrates grouped into seven classes based on traditional interpretations of gross

extant vertebrates are:[13]

In addition to these, there are two classes of extinct armoured fishes, the

paraphyletic
.

Other ways of classifying the vertebrates have been devised, particularly with emphasis on the

extinct
):

geologic ages. The width of the bubbles signifies the diversity (number of families
).

While this traditional classification is orderly, most of the groups are

phylogeny,[41]
organized by their known evolutionary history and sometimes disregarding the conventional interpretations of their anatomy and physiology.

Phylogenetic relationships

In

descendants
.

period
period