Chordates 2BIbDF09 10/11

What are Chordates ?

first give a general definition Pierre.brawand 10 janvier 2011 à 11:01 (CET) Chordates from the phylum Chordata are animals that have during the embryonic development a notochord, a hallow dorsal nerve cord, a pharyngeal gill slits, an endostyle and a postanal tail. This is mainly what differenciate them from the other Phyla. The invertebrates retain most of these features, but the vertebrates see these features evolve into more complex organs.

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)

be careful... I do not have a tail anymore.... but I'm a chordate... I did have a tail during embryongenesis... but not anymore.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 (tunicates) Vertebrata (Vertebrates):
Tetrapods
Mammals
Sauropsids
Birds
Reptiles
Amphibians
fishes
Agnata

Describe these two main subphyla of Chordates... check the textbooks... you'll find a lot of information on them...Pierre.brawand 30 janvier 2011 à 15:19 (CET)

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. 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. NathalieR 9 janvier 2011 à 18:17 (CET)

The vertebrates are the fishes , amphibianas, reptiles, bird and mammals. The particularity of the vertebrate is that it has a vertebral column. So the vertebrates can be considered as segmented animals. They have a an internal skeleton too, it's a living jointed endoskeleton, with paired appendages. Vertebrates shows cephalization, their distinc head contains the brain and exhibits special sense organs, such as camera-type eyes. Vertebrates have a large coelom and well-developed viscera : the complex digestive system is complete, having both a mouth and an anus.The blood contained entirely within blood vessels, therefore, the circulatory system is said to be closed. Vertebrates have efficient means of respiration and excretion. MelanieD 17 janvier 2011 à 11:20 (CET)

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.

However, birds are now considered as fully-fledged reptiles and thus appear in the reptilia class.

• 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)

*see Appendix Chordates 2
This phylogenetic hypothesis shows the major clades of chordates in relation to the other main deuterostome clade, Echinodermata.

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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)

Fishes

The first vertebrates werejawless fishes, which wiggled through the water and sucked up foodfrom the ocean floor.

Today there are threeclasses of fishes  :

Jawless fishes

They have smooth,scaleless skin and no jaws or paired fins. The two groups of living jawless fishes are hagfishes and lampreys. They feed mainly dead fishes. The lamprey attaches itself to another fish and taps into its circulatory system.

Cartilaginous Fishes

The rays, the skates and the sharks belong to the cartilaginous fishes. These fishes have have skeletons of cartilage, instead bone. The largest sharks, the whale sharks, feed on small fishes and marine invertebrates and do not attack humans.

Three well-developed senses enable sharks to detect their prey:

1. They can sense some electric currents in water,ven those generated by the muscle movement of animals.
2. They have a lateral line system, it allow them to sense the pressure waves caused by a fish or another animal swimming nearby.
3. They have a keen sense of smell

Bony fishes

The bony fishes are the most numerous and diverse of all vertebrates. The most common bony fishes that we eat are ray-finned fishes.

Their fins, which are used to balance and propel the body, are thin and supported by bony spikes. Ray-finned fishes have various ways of life. Some, such as hering are filter feeders and other such as piranhas and barracudas are predaceous carnivores. The ray-finned fishes have a swim bladder, which usually serves as a buoyancy organs. The streamlined shape, fins and muscle action of ray-finned fishes are all suited to locomotion the water. Their skin is covered by bony scales that protect the body but do not prevent water loss. When fishes respire, the gills are kept continuously moist by the passage of the water through the mouth and out the gill slits.MelanieD 31 janvier 2011 à 11:26 (CET)

Amphibians

Amphibians (class Amphibia), whose class name means living on both land and in the water, are represented today by frogs, toads, newts, and salamanders. Aside from jointed limbs, amphibians have other features not seen in bony fishes: eyelids for keeping their eyes moist, ears adapted to picking up sound waves, and avoice-producing larynx. Adults usually have small lungs and their hearth has only three chambers, compared to the four of mammals.

Most members of this group lead an amphibious life - that is, the larval stage lives in the water, and the adult stage lives on the land. However, the adult usually returns to the water to reproduce.

In a frog, the head and trunk are fused, and the long hind-limbs are specialized for jumping. Frogs have smooth skin, and they live in or near fresh water; toads have stout bodies and warty skin, and they live in dark, damp places away from the water. Most salamanders have limbs that are set at right angles to the body and resemble the earliest fossil amphibians. they move like a fish, with a side-to-side, S-shaped motion.NathalieR 7 février 2011 à 10:38 (CET)

Reptiles

Reptiles (class Reptilia) diversified and were most abundant between 245 and 66 MYA. These animals included themammal-like reptiles, the ancestors of today's living mammals, and dinosaurs, which became extinct, except for those that evolved into birds.

The reptiles living today are mainly alligators, crocodiles, turtles, snakes, lizards, and tuataras. The body of a reptile is covered with, keratinized scales, which protect the animal from desiccation and from predators. Reptiles have well-developed lungs enclosed by a protective rib cage and their heart has four chambers.

Perhaps the most outstanding adaptation of the reptiles is their means of reproduction, which is suitable to a land existence. Fertilization is internal, and the female lays leathery, flexible, shelled eggs. The amniotic egg made development on land possible and eliminated the need for a swimming larval stage during development.

Fishes, amphibians, and reptiles are ectotherms, meaning that their body temperature matches the temperature of the external environment. Reptiles regulate their body temperatures by exposing themselves to the sun if they need warmth or by hiding in the shadows if they need cooling off.NathalieR 7 février 2011 à 10:57 (CET)

One of the characterisctics of the birds is the presence offeathers which are modified reptilian scales. Birds lay ahard-shelled amniotic egg, rather than the leathery egg of reptiles. Ample data today indicate that birds are closely related to bipedal dinosaurs and they should be classified as such. Nearly every anatomic feature of a bird can be related to its ability to fly. The forelimbs are modified as wings. To fly they need an airstream and a powerful wing downstroke for lift, a force at right angles to the airstream. Thehollow , very light bones are laced with air cavities. A horny beak has replaced jaws equipped with teeth. Respiration is efficient, since the lobular lungs form anterior and posterior air sacs. The presence of these sacs means that the air moves one way through the lungs, and gases are continuously exchanged across respiratory tissues. Birds are endotherms and generateinternal beat. Many endotherms can use metabolic heat to maintain a constant internal temperature. Birds have particularly acute vision and well-developed brains. Their muscle reflexes are excellent. These adaptaions are suited to flight. Another aspect of bird behavior is the seasonal migration of many species over very long distances.

The classification of birds was particularly based on type of beak and foot, and to some extend on habitat and behavior.

References

• Wikipédia
• L'Aventure de la vie, Larousse
• Concepts of Biology, Sylvia S. Mader
• ...

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