Chordates 2BIbDF09 10/11

What are Chordates ?

first give a general definition Pierre.brawand 10 janvier 2011 à 11:01 (CET) More than 90% of all known chordates species have backbones (and thus are vertebrates). However, the phylum Chordata also includes three groups of invertebrates: lancelets, tunicates, and hagfishes

What are the main characteristics of Chordates ?

Chordata is the last phylum of the animal kingdom. Four characteristics distinguish them from the other animal phyla. These are the four main anatomical characteristics to identify the chordates:

1. a dorsal, hollow nerve cord
   
2. notochord
   
3. pharyngeal slits or clefts
   
4. muscular, post-anal tail
   

*see Appendix Chordates 1

Although this four anatomical characteristics distinguish the chordates from the other animal phyla, they aren't all present during the whole life of all the chordates. For example, the pharyngeal slits are seen only during the embryonic development in most vertebrates and the post-anal tail appears also only during embryogenesis for the humans( who are chordates too.)NathalieR 17 janvier 2011 à 10:51 (CET)

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be careful... I do not have a tail anymore.... but I'm a chordate... I did have a tail during embryongenesis... but not anymore. [ [Utilisateur:Pierre.brawand|Pierre.brawand]] 10 janvier 2011 à 11:01 (CET)

What are the different kinds of Chordates ?

Invertebrates Chordates

The invertebrates belong to two of the three subphylum Chordata: Urochordata and Cephalochordata. If we subdivise the phylum Chordates, it should be something like that:

Urochordata (Tunicata) Cephalochordata (acraniata) Vertebrata (Vertebrates):
Tetrapods
Mammals
Sauropsids
Birds
Reptiles
Amphibians
fishes
Agnata

An invertebrate is an an animal without a backbone.The group includes 95% of all animal species[1] – all animals except those in the chordate subphylum Vertebrata (fish, amphibians, reptiles, birds, and mammals) . An animal can be invertebrate and not belong to the chordates. NathalieR 17 janvier 2011 à 10:54 (CET)

Source: Wiki

Vertebrates Chordates

The first vertebrates appeared about 470 million years ago. They were jawless marine fishes.

Although fewer than invertebrates, the group of vertebrates form a homogeneous set of animals with anatomical characteristics in common. They owe their name to the existence of a skeleton made of bone (or cartilage in some fishes) whose essential part is the spine. All have a nervous system consisting of an anterior part, the brain, lodged in the skull, and a posterior, the spinal cord, housed in a cavity (the spinal canal) formed by all the vertebrae. They also have a circulatory system formed by the heart and blood vessels (arteries and veins), in which circulates the blood that transports oxygen for breathing.

Vertebrates are the most advanced animals and closest to the man (who is also a vertebrate). Moreover, they are almost all the useful species to man. They live in all environments, in water or on land. The first vertebrates were fishes, which some species have become amphibians. The reptiles were formed from these amphibians. Birds and mammals come from reptiles.NathalieR 9 janvier 2011 à 18:21 (CET)

Classification of the vertebrates

Vertebrates are divided into 5 main groups, or classes, each characterized by a particular lifestyle and a special anatomy.

• First appeared the fishes, during the Paleozoic era, 470 million years ago. They are aquatic animals that breathe through gills; they have no legs but fins, and their bodies are usually covered with scales. These are the most numerous and most diverse of the vertebrates: there are about 30,000 species.
• Amphibians (frogs, newts, salamanders) were formed from fishes that, 360 million years ago, began to leave the water and move onto land. These are the first vertebrates to have 4 legs; the young have gills, adults, lungs. Unlike fish, their skin is naked, that is to say, without scales. There are only 3000 species that are mainly found in wetlands.

• The reptiles were born at the end of the Paleozoic era, 290 million years ago. Most have 4 legs, but arranged in such a way that they badly support the body. That is why they move by crawling. This mode of travel is even more pronounced in snakes, which are legless reptiles. The reptiles were numerous and varied in the Mesozoic era, the so-called because of this "Age of Reptiles"(or "age of dinosaurs", which are typical reptiles at the time). It remains today only a small number of them, including turtles, crocodiles, lizards and snakes.

• Birds appeared 150 million years ago. The first "bird" known, the Archaeopteryx, is actually a kind of feathered dinosaur: he possessed both reptilian characters (teeth and a long tail) and characters of bird (feathers). Nowadays, there are about 8000 species of birds that inhabit all environments, including those coldest as the Antarctic continent.

• Mammals appeared roughly at the same time as dinosaurs, during the Mesozoic era, 200 million years ago, from very odd reptiles called "mammalian reptiles". However, they have only become numerous and varied at the Cenozoic era, about 65 million years ago, when most of the reptiles had disappeared. It is for this reason that the Cenozoic era has been called "age of mammals".Mammals are identified by their bodies covered with hair and the existence of breasts producing milk used to feed the young. Unlike other vertebrates that lay eggs (called oviparous), mammals (except the platypus) are viviparous: they give birth to fully formed young.NathalieR 9 janvier 2011 à 19:44 (CET)

this classification is oversimplified. Too simple and not correct anymore. For example, birds are now classified as REPTILES. I would generate an APPENDIX document (figure) and then describe this figure by mentioning the several characters which are used to make the classification, for example, presence of an head, or presence of jaws, or presence of lungs or fins. etc. Pierre.brawand 10 janvier 2011 à 11:01 (CET)

References

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