Respuesta :
For evolutionary biologists, the study of evolution of aquatic vertebrates into land vertebrates has been very difficult because the shift from water to land was fast and produced very few fossil records. The emergence of morphological features of tetrapods had highlighted the coelacanths and lungfish as the species of interest. Coelacanths and lungfishes are lobe-finned fishes which make them distinct from other fishes because they possess bony skeleton and not cartilage, the primary requirement in land survival. In 1938, a South African fisherman pulled a strange catch from the Indian Ocean. That strange catch was a coelacanth, a member of the clade Sarcopterygii (class of fishes including coelacanths and lungfishes) and was thought to be extinct 80 million years ago. Coelacanths has lobe-fins, that is, muscular fins with a single bone that articulates with the rest of the body. Lobe-fins are very rare in fishes but possessed by coelacanths and lungfishes. Lobe limbs, moreover, are possessed by many living organism including humans. That shows that we, tetrapods (four-limber vertebrates, mostly living in land), share a more recent common ancestor with the coelacanths and lungfishes. Tetrapods evolved from a group of organisms, which if we can see today, we would call them fish. They are aquatic with scales and fleshy fins but they have lungs to breathe oxygen. Between 390 to 360 million years, its descendants started to live in shallow waters then eventually moved to land. Because of natural selection, however, they undergone several adaptations which made these organisms more diversed and adaptive to their new terrestrial way of life. To date, we still carry the evidence of fishy origins as seen in the way our arms and legs are attached to our bodies. Early fishes had shown that lungs and gills developed early on but through time due to adaptation,lobe-fishes, the ancestors of coelacanths and lungfishes, had maintained the lungs. These lungs were later on inherited by coelacanths and lungfishes then eventually the tetrapods. Coelacanths and lungfishes, however, had maintained the gills while the tetrapods had the gills also but lost it in the course of early evolution.
Lung fishes and coelacanths are believed to be a crucial link in evolution of tetrapods from fishes as they show the presence of lobe shaped fins and lungs.
Further Explanation:
One of the major theories of evolution which supports the evolution of humans from other organism. One of the theories that link fishes to humans generally the lung fishes and coelacanths proves the link by pointing towards the fact that these species have lungs and can survive in shallow waters. Also, the presence of lobed fins is one of the character supporting the theory.
Coelacanths believed to be extinct are still found in Indian ocean and east coast of Africa. They are;
a. Latimeria chalumnae
b. Latimeria menadoensis
Lungfish that belongs to class Sarcopterygii are found in oceans and show the presence of lobe shaped fins and muscular stature. They are known to survive in shallow water as they can breathe using lungs.
Thus, the fishes (lungfish and coelacanths) are believed to be a crucial link between tetrapods and fishes.
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Answer Details:
Grade: Senior School
Subject: Biology
Topic: Evolution
Keywords:
Coelacanths, lung fishes, tetrapods, link, shallow water, sarcopterygii, Latimeria chalumnae, Latimeria menadoensis.
