Vertebrates are members of the subphylum In life, a subphylum is a taxonomic rank intermediate between phylum and superclass. The rank of subdivision in plants and fungi is equivalent to subphylum Vertebrata, chordates Chordates are animals which are either vertebrates or one of several closely related invertebrates. They are united by having, for at least some period of their life cycle, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail. The phylum Chordata consists of three subphyla: Urochordata, represented by with backbones A vertebra is an individual bone in the flexible column that defines vertebrate animals, e.g., humans. The vertebral column encases and protects the spinal cord, which runs from the base of the cranium down the dorsal side of the animal until reaching the pelvis. From there, vertebra continue into the tail or spinal columns In human anatomy, the vertebral column is a column usually consisting of 33 vertebrae, the sacrum, intervertebral discs, and the coccyx situated in the dorsal aspect of the torso, separated by spinal discs. It houses and protects the spinal cord in its spinal canal. About 58,000 species In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are often used, such as based on similarity of DNA or of vertebrates have been described.^[2] Vertebrata is the largest subphylum of chordates, and contains many familiar groups of large land animals. Vertebrates comprise cyclostomes Agnatha is a class or superclass of jawless fish in the phylum Chordata, subphylum Vertebrata. The group excludes all vertebrates with jaws, known as gnathostomes, bony fish Osteichthyes , also called bony fish, are a marellel group of fish that have bony, as opposed to blubbury, skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of over 29,000 species. It is the largest class of vertebrates in existence today. Osteichthyes is divided into the ray-finned, sharks Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago, before the time of the dinosaurs and rays Batoidea is a superorder of cartilaginous fish commonly known as rays, containing more than 500 described species in thirteen families. They are closely related to sharks, from which they can be distinguished by their flattened bodies, enlarged pectoral fins that are fused to the head, and gill slits that are placed on their ventral surfaces, amphibians Amphibians , such as frogs, toads, salamanders, newts, and caecilians, are ectothermic (or cold-blooded) animals that metamorphose from a juvenile water-breathing form, either to an adult air-breathing form, or to a paedomorph that retains some juvenile characteristics. Proteidae (mudpuppies and waterdogs) are good examples of paedomorphic species, reptiles Reptiles are animals in the class Reptilia characterized by breathing air, a "cold-blooded" (poikilothermic) metabolism, laying tough-shelled amniotic eggs (or retaining the same membrane system in species with live birth), and skin with scales or scutes. They are tetrapods (either having four limbs or being descended from four-limbed, mammals Mammals are a class of vertebrate, air-breathing animals whose females are characterized by the possession of mammary glands while both males and females are characterized by hair and/or fur, three middle ear bones used in hearing, and a neocortex region in the brain. Some mammals have sweat glands, but most do not, and birds Birds are winged, bipedal, endothermic (warm-blooded), egg-laying, vertebrate animals. There are around 10,000 living species, making them the most varied of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from the 5 cm (2 in) Bee Hummingbird to the 2.75 m (9 ft) Ostrich. Extant vertebrates range in size from the carp Carp is a common name for various species of an oily freshwater fish of the family Cyprinidae, a very large group of fish native to Europe and Asia. The cypriniformes is traditionally grouped with the Characiformes, Siluriformes and Gymnotiformes to create the superorder Ostariophysi, since these groups have certain common features such as being species Paedocypris Paedocypris is an Indonesian genus of fish in the family Cyprinidae . Previously the two species, Paedocypris progenetica and Paedocypris micromegethes were known. In 2006 however, an undescribed third species was discovered in Bukit Bauk, Terengganu in Malaysia, at as little as 7.9 mm (0.3 inch), to the Blue Whale The Blue whale is a marine mammal belonging to the suborder of baleen whales (called Mysticeti). Blue Whales can reach up to 33 metres (108 ft) in length and 180 metric tons (200 short tons) or more in weight. In volume, it is currently the largest animal existing or known to have existed, at up to 33 m (110 ft). Vertebrates make up about 5% of all described animal species; the rest are invertebrates An invertebrate is an animal without a backbone. The group includes 95% of all animal species — all animals except those in the chordate subphylum Vertebrata, which lack backbones.

The vertebrates traditionally include the hagfish Hagfish are marine craniates of the class Agnatha or Myxini, also known as Hyperotreti. Some researchers regard Myxini as not belonging to the subphylum Vertebrata. That is, they are the only living animals that have a skull but not a vertebral column, which do not have proper vertebrae, though their closest living relatives, the lampreys A lamprey is a parasitic marine/aquatic animal with a toothed, funnel-like sucking mouth. Translated directly, their name means stone lickers (lambere: to lick, and petra: stone). While lampreys are well known for those species which bore into the flesh of other fish to suck their blood, these species make up the minority. In zoology, lampreys are, do have vertebrae.^[3] For this reason, the sub-phylum is sometimes referred to as "Craniata Craniata is a proposed clade of chordate animals that contains the Myxini (hagfish), Petromyzontida (including lampreys), and Gnathostomata (jawed vertebrates) as living representatives. As the name suggests, Craniata is animals with a (hard bone or cartilage) skull in Chordata", as all members do possess a cranium The skull is a bony structure in the head of many animals that supports the structures of the face and protects the brain from injury.

Etymology

The word vertebrate derives from Latin vertebratus (Pliny Naturalis Historia is an encyclopedia published circa AD 77-79 by Pliny the Elder. It is one of the largest single works to have survived from the Roman empire to the modern day and purports to cover the entire field of ancient knowledge, based on the best authorities available to Pliny. He claims to be the only Roman ever to have undertaken such), meaning having joints.^{[citation needed]} It is closely related to the word vertebra A vertebra is an individual bone in the flexible column that defines vertebrate animals, e.g., humans. The vertebral column encases and protects the spinal cord, which runs from the base of the cranium down the dorsal side of the animal until reaching the pelvis. From there, vertebra continue into the tail, which refers to any of the bones or segments of the spinal column.^[4]

Anatomy and morphology

All vertebrates are built along the basic Chordate Chordates are animals which are either vertebrates or one of several closely related invertebrates. They are united by having, for at least some period of their life cycle, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail. The phylum Chordata consists of three subphyla: Urochordata, represented by body plan A body plan is essentially the blueprint for the way the body of an organism is laid out. An organism's symmetry, its number of body segments and number of limbs are all aspects of its body plan. One of the key issues of developmental biology is the evolution of body plans as different as those of a starfish, a fern, or a mammal, from a common: A stiff rod running through the length of the animal (vertebral column In human anatomy, the vertebral column is a column usually consisting of 33 vertebrae, the sacrum, intervertebral discs, and the coccyx situated in the dorsal aspect of the torso, separated by spinal discs. It houses and protects the spinal cord in its spinal canal or notochord The notochord is a flexible, rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo. In some chordates, it persists throughout life as the main axial support of the body, while in most vertebrates it is replaced by the vertebral column. The notochord is), with a hollow tube of nervous tissue (the spinal cord The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain . The brain and spinal cord together make up the central nervous system. The spinal cord extends down to the space between the first and second lumbar vertebrae; it does not extend the entire length of the vertebral column. It is around 4) above it and the gastrointestinal tract The Human gastrointestinal tract or digestive system is the system by which ingested food is acted upon by physical and chemical means to provide the body with nutrients it can absorb and to excrete waste products; in mammals the system includes the alimentary canal extending from the mouth to the anus, and the hormones and enzymes assisting in 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 aft of the anus forms a tail The tail is the section at the rear end of an animal's body; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals and birds. While tails are primarily a feature of vertebrates, some invertebrates including scorpions and springtail, as with vertebrae and spinal cord, but no gut.

The defining characteristic of a vertebrate is the vertebral column In human anatomy, the vertebral column is a column usually consisting of 33 vertebrae, the sacrum, intervertebral discs, and the coccyx situated in the dorsal aspect of the torso, separated by spinal discs. It houses and protects the spinal cord in its spinal canal, in which the notochord (a stiff rod of uniform composition) 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, as in the sturgeon Sturgeon is the common name used for some 26 species of fish in the family Acipenseridae, including the genera Acipenser, Huso, Scaphirhynchus and Pseudoscaphirhynchus. The term includes over 20 species commonly referred to as sturgeon and several closely related species that have distinct common names, notably sterlet, kaluga and beluga. Jawed vertebrates Gnathostomata is the group of vertebrates with jaws. The term derives from Greek γνάθος (gnathos) "jaw" + στόμα (stoma) "mouth" are typified by paired appendages (fins or legs, which may be secondarily lost), but this is not part of the definition of vertebrates as a whole.

Evolutionary history

Vertebrates originated about 525 million years ago during the Cambrian explosion The Cambrian explosion or Cambrian radiation was the relatively rapid appearance, over a period of many million years, of most major groups of complex animals around 530 million years ago, as found in the fossil record. This was accompanied by a major diversification of other organisms, including animals, phytoplankton, and calcimicrobes. Before, which was an event of massive rise in organism diversity that occurred in the Cambrian The Cambrian is the first geological period of the Paleozoic Era, lasting from 542 ± 0.3 million years ago to 488.3 ± 1.7 million years ago(ICS, 2004,; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the classical name for period. The earliest known vertebrate is believed to be the Myllokunmingia Myllokunmingia is a chordate from the Lower Cambrian Maotianshan shales of China, thought to be a vertebrate, although this is not conclusively proven. It is 28 mm long and 6 mm high.^[1] Molecular analysis since 1999 have suggested that the hagfishes Hagfish are marine craniates of the class Agnatha or Myxini, also known as Hyperotreti. Some researchers regard Myxini as not belonging to the subphylum Vertebrata. That is, they are the only living animals that have a skull but not a vertebral column are most closely related to lampreys, and so also are vertebrates. Others consider them a sister group of vertebrates in the common taxon of Craniata Craniata is a proposed clade of chordate animals that contains the Myxini (hagfish), Petromyzontida (including lampreys), and Gnathostomata (jawed vertebrates) as living representatives. As the name suggests, Craniata is animals with a (hard bone or cartilage) skull in Chordata.^[3][5] Another early vertebrate is Haikouichthys ercaicunensis, also from the Chengjiang Chengjiang County is located in Yuxi, Yunnan Province, China, just north of Fuxian Lake fauna 524 million years ago. All of these groups lacked a jaw The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term jaws is also broadly applied to the whole of the structures constituting the vault of the mouth and serving to open and close it and is part of the body plan of most animals in the common sense.

The first jawed vertebrates Gnathostomata is the group of vertebrates with jaws. The term derives from Greek γνάθος (gnathos) "jaw" + στόμα (stoma) "mouth" appeared in the Ordovician The Ordovician [/ɔɹdəˈvɪʃən/] is a geologic period and system, the second of six of the Paleozoic Era, and covers the time between 488.3±1.7 to 443.7±1.5 million years ago (ICS, 2004,. It follows the Cambrian Period and is followed by the Silurian Period. The Ordovician, named after the Welsh tribe of the Ordovices, was defined by Charles and became common in the Devonian The Devonian is a geologic period and system of the Paleozoic Era spanning from 416 to 359.2 million years ago (ICS, 2004,. It is named after Devon, England, where rocks from this period were first studied, often known as the "Age of Fishes". The two groups of bony fishes, the actinopterygii The ray-finned fishes are so called because they possess lepidotrichia or "fin rays", their fins being webs of skin supported by bony or horny spines , as opposed to the fleshy, lobed fins that characterize the class Sarcopterygii which also, however, possess lepidotrichia. These actinopterygian fin rays attach directly to the proximal and sarcopterygii Sarcopterygii -- sometimes considered synonymous with Crossopterygii ("fringe-finned fishes", from Greek κροσσός, krossos, fringe) is a clade (traditionally a class or subclass) of fleshy-finned or lobe-finned fishes, the living descendants of which are the coelacanths, lungfishes and all tetrapods, evolved and became common. The Devonian also saw the demise of virtually all jawless fishes, save for lampreys and hagfish, as well as the rise of the first labyrinthodonts Labyrinthodont is an obsolete term for any member of the extinct superorder (or subclass) (Labyrinthodontia) of amphibians, which constituted some of the dominant animals of Late Paleozoic and Early Mesozoic times (about 350 to 210 million years ago). The name describes the pattern of infolding of the dentine and enamel of the teeth, which are, transitional between fish and amphibians Amphibians , such as frogs, toads, salamanders, newts, and caecilians, are ectothermic (or cold-blooded) animals that metamorphose from a juvenile water-breathing form, either to an adult air-breathing form, or to a paedomorph that retains some juvenile characteristics. Proteidae (mudpuppies and waterdogs) are good examples of paedomorphic species. The Placodermi The Placodermi were a class of armoured prehistoric fish, known from fossils, which lived from the late Silurian to the end of the Devonian Period. Their head and thorax were covered by articulated armoured plates and the rest of the body was scaled or naked, depending on the species. Placoderms were among the first jawed fish; their jaws likely, a group of fishes that dominated much of the late Silurian and the majority of the Devonian period, also became extinct at the end of the Devonian.

The reptiles Reptiles are animals in the class Reptilia characterized by breathing air, a "cold-blooded" (poikilothermic) metabolism, laying tough-shelled amniotic eggs (or retaining the same membrane system in species with live birth), and skin with scales or scutes. They are tetrapods (either having four limbs or being descended from four-limbed appeared from labyrinthodont stock in the subsequent Carboniferous The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Ma , to the beginning of the Permian Period, about 299.0 ± 0.8 Ma (ICS, 2004, period. The anapsid and synapsid reptiles were common during the late Paleozoic, while the diapsids became dominant during the Mesozoic. The dinosaurs gave rise to the birds in the Jurassic. The demise of the dinosaurs at the end of the Cretaceous promoted expansion of the mammals, which had developed from the therapsids, a group of synapsid reptiles, during the Late Triassic Period.

Classification

There are several ways of classifying animals. Evolutionary systematics relies on anatomy, physiology and evolutionary history, which is determined through similarities in anatomy and, if possible, the genetics of organisms. Phylogenetic classification is based solely on phylogeny. Evolutionary systematics gives an overview; phylogenetic systematics gives detail. The two systems are thus complementary rather than opposed.^[6]

Traditional classification

Conventional classification has living vertebrates grouped into seven classes based on traditional interpretations of gross anatomical and physiological traits. This classification is the one most commonly encountered in school textbooks, overviews, non-specialist, and popular works:^[7]

• Class Agnatha (jawless fish)
• Class Chondrichthyes (cartilaginous fishes)
• Class Osteichthyes (bony fishes)
• Class Amphibia (amphibians)
• Class Reptilia (reptiles)
• Class Aves (birds)
• Class Mammalia (mammals)

While this traditional classification is orderly, it is frequently considered to be inaccurate phylogenetically, as most of the groups are paraphyletic, i.e. do not contain all descendants of the class's common ancestor. Descendants of the first reptiles do for instance include the birds and mammals as well as reptiles. Quite a few scientists working with vertebrates use a classification based purely on phylogeny, organized by their known evolutionary history and sometimes disregarding the conventional interpretations of their anatomy and physiology. An example based on Janvier (1981, 1997), Shu et al. (2003), and Benton (2004)^[8] is given here:

• Subphylum Vertebrata
  • Superclass Agnatha or Cephalaspidomorphi (lampreys and other jawless fishes, some ancestral to other vertebrates)
  • Infraphylum Gnathostomata (vertebrates with jaws)
    • • Class †Placodermi (extinct armoured fishes)
      • Class Chondrichthyes (cartilaginous fishes)
      • Class †Acanthodii (extinct spiny "sharks")
      • Superclass Osteichthyes (bony fishes)
        • Class Actinopterygii (ray-finned bony fishes)
        • Class Sarcopterygii (lobe-finned fishes, some ancestral to tetrapods)
      • Superclass Tetrapoda (four-limbed vertebrates)
        • Class Amphibia (amphibians, some ancestral to the amniotes)
        • Class †Synapsida (extinct mammal-like "reptiles", some ancestral to mammals, sometimes classed with Reptilia)
        • Class Mammalia (mammals)
        • Class Reptilia (reptiles, some ancestral to birds)
        • Class Aves (birds)

Most of the classes listed are not "complete" taxa: the agnathans have given rise to the jawed vertebrates; the bony fishes have given rise to the land vertebrates; the traditional "amphibians" have given rise to the reptiles (traditionally including the mammal-like "reptiles"), which in turn have given rise to the birds and mammals.

Phylogenetic relationships

In phylogenetic taxonomy, the relationships between animals are not typically divided into ranks, but illustrated as a nested "family tree" known as a cladogram. Phylogenetic groups are given definitions based on their relationship to one another, rather than purely on physical traits such as the presence of a backbone. This nesting pattern is often combined with traditional taxonomy (as above), in a practice known as evolutionary taxonomy.

The cladogram presented below is based on studies compiled by Philippe Janvier and others for the Tree of Life Web Project.^[9]

See also

• Invertebrate
• Marine vertebrates

References

1. ^ ^{a b} Shu et al.; Luo, H-L.; Conway Morris, S.; Zhang, X-L.; Hu, S-X.; Chen, L.; Han, J.; Zhu, M. et al. (November 4, 1999). "Lower Cambrian vertebrates from south China". Nature 402: 42–46. doi:10.1038/46965.
2. ^ Jonathan E.M. Baillie, et al. (2004). "A Global Species Assessment". World Conservation Union. http://www.iucn.org/bookstore/HTML-books/Red%20List%202004/completed/table2.1.html.
3. ^ ^{a b} Kuraku et al.; Hoshiyama, D; Katoh, K; Suga, H; Miyata, T (December 1999). "Monophyly of Lampreys and Hagfishes Supported by Nuclear DNA–Coded Genes". Journal of Molecular Evolution 49 (6): 729. doi:10.1007/PL00006595. PMID 10594174.
4. ^ Douglas Harper, Historian. "vertebra". Online Etymology Dictionary. Dictionary.com.. http://dictionary.reference.com/browse/vertebra.
5. ^ Nicholls, Henry (10 September 2009). "Mouth to Mouth". Nature 461 (7261): 164–166. doi:10.1038/461164a. PMID 19741680.
6. ^ Hildebran, M. & Gonslow, G. (2001): Analysis of Vertebrate Structure. 5th edition. John Wiley & Sons, Inc. New York, page 33: Comment: The problem of naming sister groups
7. ^ Romer, A.S. (1949): The Vertebrate Body. W.B. Saunders, Philadelphia. (2nd ed. 1955; 3rd ed. 1962; 4th ed. 1970)
8. ^ Benton, Michael J. (2004-11-01). Vertebrate Palaeontology (Third ed.). Blackwell Publishing. pp. 455 pp.. ISBN 0632056371/978-0632056378. http://palaeo.gly.bris.ac.uk/benton/vertclass.html.
9. ^ Janvier, Philippe. 1997. Vertebrata. Animals with backbones. Version 01 January 1997 (under construction). http://tolweb.org/Vertebrata/14829/1997.01.01 in The Tree of Life Web Project, http://tolweb.org/

Bibliography

• Kardong, Kenneth V. (1998). Vertebrates: Comparative Anatomy, Function, Evolution (second ed.). USA: McGraw-Hill. pp. 747 pp.. ISBN 0-07-115356-X/0-697-28654-1. http://www.amazon.com/Vertebrates-Comparative-Anatomy-Function-Evolution/dp/0072909560.
• "Vertebrata". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=331030. Retrieved 6 August, 2007.

External links

• Tree of Life
• Tunicates and not cephalochordates are the closest living relatives of vertebrates
• Vertebrate Pests chapter in United States Environmental Protection Agency‎ and University of Florida/Institute of Food and Agricultural Sciences National Public Health Pesticide Applicator Training Manual

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