Amphibians are grouped in phylum chordate, subphylum of vertebrate and class amphibian. These Vertebrates comprise of many living chordates, and they have evolved an enormous variety of forms. This is divided into eight classes; four are aquatic which is grouped into super class Pisces, while four are terrestrial. They are grouped as super class Tetrapods or four-footed animals.


They have different movement aquatic species like fish moves by weaving of the trunk and tails, most of them have sets of paired fins pelvic and pectoral they do not have limbs. The terrestrial species move in the form of wriggling which is similar to those of fish even though it has limbs that support the movement.


Some have limbs that make movement simple, like Frogs and toads use their muscular hind legs for jumping. While other amphibians have lost their limbs and most of that species are burrowing forms.


As evolution are taking place basic forms of structure evolve to perform number of task, example tetrapods, forelimbs becomes used for grasping climbing, flying, burrowing and swimming as well as terrestrial locomotion. In amphibians, limbs improved for locomotion. These evolve into upright position which is different to what amphibian have of sprawling, and have some tendency towards bipedalism among reptiles and birds.


All these changes in limbs evolve from fish and the vertebrates that start to evolve on land it was suggested by scientist that many of limb and muscles developments needed for walking on land before fish and limbed animals split.


When Tetrapods moved onto land they lose connection between the skull and the pectoral girdle as they move on land. The pelvic girdle became closely involved with vertebral column using the sacral vertebrae. While in fish the pelvic is made up of one
And basiterygium (paired bone). In amphibians, the basiterygium divided into the ilium and ischium. Because the pectoral girdles are not attached to the head of terrestrial animal no force of walking can be send directly into skull which shocks the brain. Amphibians did not obtain the strong girdles like fish, because they evolved from fish.


Loss of limbs is very common in all lineages of vertebrates, this because fishes and amphibians, has evolved many times and they all move by the use of the limbs. While if mammals or archosaurs were to lose their limbs, their axial muscular would still be weak and unable to support the animal.


Only one group of mammal (whales) have ever lost either of the limbs. Whales develop a larger, broad tail which is considerably strengthened their axial muscular. Whales and snakes are animals which have lost limbs and are still retain some element of the girdles


In conclusion changes in adaptation tend to evolve in the change of structural patterns of the species, this result because some of the species live in both environment and they would like to have features that will allow them to move. so evolving of limbs in amphibians and vanishing of limbs are also influenced by the environment that they choose to live in,


Reference:

1 Limb evolution [internet] [cited 2006-May-09] Available from: http://sellers.sbc.man.ac.uk/~wis/lectures/limb-evolution/LimbEvolution.html


2. Amphibians [internet] [cited 2006-may-09] Available from: http://web6.duc.auburn.edu/academic/classes/zy/0301/Topic9/topic9.pdf


Mr Elelwani Muanalo
NISL- Ecological Informatics Student
CSIR Pretoria
Tel: +27 12 841 2133
Fax: +27 12 842 7024.
Email: emuanalo@csir.co.za
My bloger URL: http://www.emuanalo.blogspot.com

Fish have various groups, which is made up of three living classes that hold an important place in evolution history and modern ecology. Fish are the first known vertebrate (animals with backbones) and also the first species that evolve in land –walking vertebrates, they are the first known true chordate that has been found. (1)


It was suggested that fish evolve before the Devonian periods which was referred as the Age of fishes, fishes where aquatic species. Then at the end of Devonian periods tetrapods (vertebrate) which evolved legs which they can be used to walk on land evolve, and this evolution led to the adaptation to land in the form of amphibians.(1)


Ostracoderms was the first fish to evolve in the period of Cambrian about 510 million years ago and became extinct at the end of the Devonian periods it was jawless fishes found in the aquatic environment, it was covered by scales this Ostracoderms were less than 30cm long and it was placed in the class of Agnathans. These jawless fishes were the first vertebrates. Jawless fish was having circular mouth with a sharp spine tongue which is used for sucking and filtering food. Most of the species under this class agnath was not having fins except for a fringe around the tail, And they possesses the beginning of the backbone in a form of cartilaginous. (3)


In agnath group they were other small fish like animal which possessed heavy protective covering –plating, this was originated from the deposit of salts from food they eat. This plating was suggested that it tend to harden the gill arches to become the upper jaw and the bottom gill into lower jaws. And this evolution of jaws on fishes was important because it permit the fish to feed on variety of foods. Having jaws allowed them to be vigorous hunters as opposed to passive filter feeder. Being vigorous hunters led the fish to have large diversity of adaptations.(3)


This salt deposit marks the first presents of bone in the fishes which influence the evolution of vertebrates. The bony plate provides protection against sea scorpions that co-existed at the same time.(1)


Some of the bony scales in the skin around the mouth enlarge and became first teeth, while the lateral flaps of skin evolved into true fins which improve the swimming. Because of the food they eat with salts, lots of features evolved other develop some back bones. Species such as Acanthodii develop internal bony skeleton running longitudinal through the body. And this type of species was likely the ancestor of the bony fish we know today. (3)


Bony fish are often regarded as "true" fish. This group includes most of the fish we are familiar with to day. They are characterised by short jaw with lower jaw articulates with vertical quadrate it also have symmetrical caudal fin for swimming. They also have bony skeleton and single pair gill opening this are the advance bony fish we have today in the class of vertebrate. (2)


In general there is much to be learned from fish, they have evolved to fill every aquatic and inland environment with variety of adaptation. Fishes are important in evolutionary steps they are the first known vertebrate and also influence the evolution of all living vertebrate on land.

Reference:


1. Kagle R.1997.The Evolutionary Steps Of Fish [internet] [cited 2006- May -08] Availablefrom:http://serendip.brynmawr.edu/biology/b103/f97/projects97/Kagle.html


2. Fish Distribution [Internet] [cited 2006-May-08] Available from: http://www.lookd.com/fish/distribution.html


3. The Major Radiation of Fishes;[Internet][ cited 2006-May-08] Available from:http://users.tamuk.edu/kfjab02/Biology/Vertebrate%20Zoology/b3405_ch08.htm


4. Wikipedia contributors. Osteichthyes. [Internet] Wikipedia, the Free Encyclopedia; 2006 May 07. [Cited 2006-May-08]Available from: http://en.wikipedia.org/wiki/Osteichthyes



Mr Elelwani Muanalo
NISL- Ecological Informatics Student
CSIR Pretoria
Tel: +27 12 841 2133
Fax: +27 12 842 7024.
Email: emuanalo@csir.co.za
My bloger URL: http://www.emuanalo.blogspot.com