Biodiversity

Thursday, May 11, 2006

THE REASONS WHY SOME OF AMPHIBIANS BECAME LIMBLESS.

The amphibians are the simplest Tetrapods from the first class of the vertebrate to occupy the land. The Tetrapods includes approximately 18100 existing species of amniotes and approximately 300 existing species of amphibians. Tetrapoda refers to the species with four feet and it forms the largest group of the global vertebrates (Frank et al, 1995).

Some of the known amphibians animals, which lost their limbs or became limbless animals, include snakes and whales (2).

The loss of the limbs seems to be very common in all lineages of vertebrates. Both the fishes and the amphibians evolved several times and they both move by using the limbs. There is at least one group of mammal (whales) that never lost either of their limbs. They survived only because they developed a larger, broad tail which significantly strengthened their axial muscular. Some of the amphibians lost their limbs because the axial muscular mammals and the archosaurs were not able to support them. These animals lost their limbs because of the environmental conditions which were not stable (2).


Reasons were suggested on why the snake became limbless. It was suggested that the snake might have “burrowed underground searching for food in small crevices” (2). I tend to agree with this suggestion, because even to date snakes spent much of their times in small holes (hibernate). Most of the times, snake are seen during summer times, when they are searching for foods and sometimes when they are feeling hot in their habits. The snakes lost their limbs when they were struggling to enter the small holes” (2). There was not a way that the snake could have limbs after losing their limbs supporters (2).


According to the information gathered, it really shows that some of the amphibians became limbless, because their common ancestors are having four limbs. The two are found in front and another two at the back. When we talk about the limb we are referring to a leg, wing or an arm of an animal. The two major hypotheses called the fin – fold and the gill arch hypotheses explain better about the original of the limbs (3).


In conclusion, the amphibians lost their limbs because of the unstable environmental conditions and also because some of the amphibians were going underground to search for their food, by so doing they injured their pelvic that was then when they became limbless (2).

1. SeaWorld/Busch Gardens Animal Information Database. (2002) [http://www.buschgardens.org/infobooks/KillerWhale/adapaqkw.html, accessed on 09/05/2006, 10:00].


2. Scientific American. (2005). [http://www.scientificamerican.com/print_version.cfm?articleID=000DC8B8-EA15-137C-AA1583414B7F0000 , accessed on 10/05/2006, 12:30].


3. Frank H.T, Shaffer P.R, Perlman R. 1995. Fossils a Guide to Prehistoric Life. Page (139)


Ms Evelyn Maleka
CILLA CSIR
P.O. Box 395
Pretoria,
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Tel: (012) 841 2133
Fax: 012 842 7024.
Email:emaleka@csir.co.za
http://malekaevelyn.blogspot.com/

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