Vertebrate

Exemplary representatives of the five classical groups of vertebrates: Fire salamanders ( amphibians), saltwater crocodile ( reptile ), cassowary ( birds), Rotschulter - elephant shrew (mammal ), sunfish ( fish)

As vertebrates ( Vertebrata ) all animals are referred to that have a spine. These include mammals ( Mammalia), birds ( Aves ), reptiles and amphibians, bone and cartilaginous fish; also lampreys ( Petromyzontida ) and the hagfish ( Myxini ), which, like some very original bony fishes (eg the coelacanth ) and the chimaeras ( Chimaeriformes ) still have no spine from the class of cartilaginous fish, but a notochord. By many researchers, the term craniotes ( Craniata ) is therefore now preferred because owning a ossified or consisting of cartilage skull or a cartilaginous head skeleton ( in lampreys and hagfish ) is really all vertebrates own, and thus one of the basic patterns of the group.

Vertebrates are found worldwide, living on all continents including Antarctica, the ocean to the deep sea, in freshwater and on land in all habitats including the high mountains. Birds and bats have the ability to active flight. Today there are about 58,000 species of vertebrates, more than half of them are fish. These are estimates that about one percent of all species that have appeared in the course of vertebrate evolution. In addition, so far tens of thousands of fossil species have been discovered around the world.

Another striking feature that distinguishes vertebrates from all other multicellular animals, their body size. Most invertebrates are only a few inches tall, sizes, that must be specified in millimeters, are very common here. Exceptions among the invertebrates, only the cephalopods, some crustaceans ( lobster, crayfish ) and giant clams. Vertebrates from a few centimeters in size, however, are always among the smallest species of their taxon. The smallest aquatic vertebrates are some gobies (eg Schindleria brevipinguis ) and carp fish (eg Paedocypris progenetica with a length of 7.9 mm for females and 10 mm for males ), smallest land vertebrate, the frog Paedophryne amauensis ( with a length of 7.7 mm). The Etruscan shrew ( Suncus etruscus ) with a hull length of 2 cm and a weight of 1 g and the bumblebee bat ( Craseonycteris thonglongyai ) with a weight of 1.5 to 3 g are considered the smallest mammals. The largest vertebrate is, with a maximum length of 30 m and a maximum weight of 200 tons, the blue whale (Balaenoptera musculus), the largest land vertebrate, the African Desert Elephant (Loxodonta africana) with a maximum weight of 7 tons. The largest vertebrate animals of the mainland were the sauropod ( Sauropoda ), a very diverse group of dinosaurs.

Reason for this associated with the emergence of vertebrates increase in size in the animal kingdom is their unique, composed of bone and cartilage internal skeleton, the development of a very powerful muscles and a closed cardiovascular system.

The vertebrates have in conventional biological systematics the rank of sub- base and together with the tunicates and the species-poor acrania the trunk of the chordates ( Chordata ).

Basic plan

The monophyly of the vertebrates is supported by a set of shared derived ( new ) basic plan features ( synapomorphies ):

• Multilayered epidermis: The epidermis differentiates into several superimposed layers of cells. Within the vertebrates is the formation of the " skin " with several layers and associated structures, such as scales, feathers, etc.
• Neurocranium: the brain and the major sense organs are protected by a capsule.
• Neural Crest: An embryonic structure from pluripotent cells, which arise from the ectoderm at the border between epidermal ectoderm and neural ectoderm. They are, among other skeletal structures of the head, pigment cells, neural cells, such as Rohon - Beard cells, ganglion and odontoblasts.
• Placoden: thickening of the embryonic epidermis. Cells of the Placoden are involved in the formation of neural organs
• Labyrinth Organ: The organ of balance
• Brain: The anterior part of the neural tube is differentiated to a ( multi-part ) brain.
• Cranial nerves: The ground floor has ten nerves completely different nature, that connect the brain to the periphery. They are quite constantly present throughout the vertebrates.
• Dorsal root ganglia: the spinal ganglia can be assigned.

Systematic position within the chordates

After Notochordata - Urochordata hypothesis that vertebrates are considered as sister group of the acrania ( acrania / Cephalochordata ), ( Craniata or Craniata ) so they are often referred to as " skull animals " means. The alternative, later published Olfactores - Cephalochordata - hypothesis, however, that the tunicates ( Urochordata / Tunicata ) is the sister group of vertebrates. Which hypothesis is correct, is still not yet clear.

Inside systematics

The internal classification of vertebrates is controversial. At the moment, the most likely hypothesis is a sister group relationship between lampreys and pine animals. The hagfish, in turn, are using this approach sister group of these two groups.

This system contradicts the old " agnathans " hypothesis: This is a sister group relationship between lampreys and hagfish is assumed which are compared with taxon as " jawless " the pine animals. This is justified by the absence of a jaw. However, this is an original feature which divide the two groups with all non- pine animals ( a Symplesiomorphie ) and thus for the relationship analysis insignificant.

System

• Vertebrates ( Vertebrata ) ( 57,850 species) Cyclostomes ( cyclostomes ) Hagfish ( Myxini ) ( 74 species )
• Lampreys ( Petromyzontida ) ( 42 species )

• Placodermi † ( paraphyletic )
• Acanthodii † ( paraphyletic )
• Cartilaginous fishes ( Chondrichthyes ) ( 1143 species)
• Bony fishes ( Osteichthyes ) Ray-finned fishes ( Actinopterygii ) ( 26,000 species )
• Meat -finned fishes ( Sarcopterygii ) ( 8 species)

• Amphibians ( Amphibia ) ( 6,400 species)
• Amniotes ( 24,200 species) Sauropsida ( paraphyletic Reptiles ( Reptilia )) ( 8,700 species) and birds ( Aves) (10,000 species)
• Mammals (Mammalia ) ( 5,500 species)

The membership of another group to the Vertebrata, the conodonts is controversial. The extinct, often heavily armored, jawless taxa are summarized as Ostracodermi, armored, jawed as placoderms. However, the two groups are not monophyletic taxa that Acanthodii which are neither part basal to cartilaginous fish or bony fish.