The living fossils: coelacanth Celeste Thomas Department of biodiversity and conservation biology University of the western cape Private bag x17 Bellville 7535 firstname.lastname@example.org
The coelacanth classification are as follows. Kingdom: animalia Phylum : chordate Class : sarcoterygii Order : coelacathiformes Family : latimeriidae Genus : latimeria http:// en.wikipedia.org/wiki/coelacanth Classification
The living vertebrates consists mainly of two groups in the modern classification. The Gnasthostomata and the jawless Agnatha are divided into two groups cartilaginous chondrithyes and bony Osteichthyes. The actinopterygii and sarcpoterygii are the two main groups of the bony vertebrates. The latter comprises of three groups the coelacanth, lungfishes and the four-limbed tetrapods. The sarcopterygii is applied to a group comprising the coelacanth and the lungfishes. Origin of the coelacanth
A modern scientist J L B Smith thus believed that four-legged land dwellers evolved from the extinct groups like the coelacanth. • However, although the coelacanth share characteristics with early land dwellers the lungfishes shared more. • Thus few scientist believe that the coelacanth is the missing link. • The research that has been done showed that the coelacanth latimeria chalumnae has not radically evolved from the way coelacanths appeared millions of years ago. • Thus by studying latimeria chlumnae is studying an ancient fossil that is alive.
The Crossopterygii and Dipnoi were the only vertebrates orders between Devonian period and recent times. • The choanichthyes is made up by crosspterygii and dipnoi. • The rhipidistia and coelacanthini are two suborders included in crossopterygii. • The rhipistians however, became extinct in early Permian. • Even though the rhipidistians became extinct in the early Permian, they were important because they gave rise to the tetrapods as well as to the coelacanths. • The lungfishes were derived from the primitive rhisidistians or from their common ancestral group. • In the middle Devonian were the coelacanth already well defined. • http://links.jstor.org/sici=0.014-3820(195203)
Fossil records • Thus the coelacanths studied by scientist since 1839 were only through their fossils. • The fossil fish Coelacanthus granulatus were found by Louis Agassiz. • Over the next century scientists had found fossils of dozens of species of coelacanth. • 400 million years ago was the appearance of the earliest fossils, while the most recent were 70 million years ago. • Thus according to the fossils record coelacanths disappeared completely.
Although only two representatives present, as a group the coelacanths were once successful. • These species left abundant fossil record from Devonian to the cretaceous period. • The coelacanth have been known to remain unchanged for millions of years. • Macropoma a extinct genus of crustaceous resembled the living specie. • http://en.wikipedia.org/wiki/Coelacanth#Biological_characteristcs
Marjorie courtenary-latimer were first person that discovered the specimen in 1938 in coastal waters of South African. The coelacanth were not particularly successful in total numbers of distinct genera even in spit of their long history. The discovery http://en.wikipedia.org/wiki/Coelacanth #Biological_characteristcs
The diversity of these fishes reached a peak in Triassic, only with 11 genera of this period. • The Devonian coelacanth has been found in marine formations suggesting marine origin. • Thus negative evidence were available that showed coelacanth deserted marine environment by missippian.
The carboniferous and Permian coelacanths occurred in freshwater sediments and Triassic genera were about 60% marine. • The lungfishes were equally well defined group. • They arose in early Devonian having same total number of genera like coelacanthini.( http://links.jstor.org/sici=0.014-3820(195203)
The Anatomy • Major unique features are present that distinguishes among the coelacanth and other fishes. • This involves aspects like external forms, skeleton anatomy etc. • The feature in the coelacanth in particular being the extra tail the epicaudal. • The fins of coelacanth are also different instead of 1 dorsal fins they have 2. • Dentricales are present which aids in protection. http://www.pds.org/gbh/nova/fish
The skeleton of the coelacanth was also different from modern fishes. • The skeleton were made mostly of cartilage. • A notochord, which are fibrous, elasticity are usually thick walled in coelacanth. • Thus most creatures with backbones, have vertebrae which replaces their notochord.
The head region of the coelacanth is also a mystery. • It is occupied by 6 small holes , two near each eye and two towards the tip of the snout. • This identification was never observed in coelacanth fossils. • These strange holes led to a space in the coelacanths head in which this cavity had never been seen in a living fish. • The six holes were an outer opening of a tube filled with jelly-like substances. • The rostral organ are formed together by the tube and cavity . • Thus this organ has unique functions which are not observed in modern fishes.
The eye features of the coelacanth is normally large which is attached to the optic nerves. • The presence of color rods assist the coelacanth in vision. • The brain is quit small and occupies about 1.5 percent of the braincase in mature individuals it differs in the pups. • The gills of the coelacanth normally indicates that they found in depth of 500-800m. (http://www.pbs.org/wgbh/nova/fish/anatomy.html)
Locomotion • The coelacanth has unique ways of swimming and gliding through the water. • Their lobed pectoral and pelvic fin move similar to the way a son moves his arms. • In spite of thickness of fins they quit flexible. • When swimming pairs lobed fins move the way horses legs do when trots. • A intentional fin locomotion is thus unique to the coelacanth.
The coelacanth rests close to the bottom of the ocean bed. • Its fins are used for many functions like balance and steering as it swims. • To escape its prey the fish uses its large thick, caudal fin. • The coelacanth thus has limited energy, it only swims fast enough to escape its predator.
Hunting • The coelacanth are usually opportunistic feeders, hunting on cuttlefish, squids etc • They are known to be nocturnal with unique feeding habits. • Instead of hunting in packs they usually hunt alone. • They usually allowed themselves to be steered by the water currents. • This type of hunting displayed by the coelacanth is called drift hunting.
Its natural habitat • The coelacanth in its natural habitat are distinguish from one another by having white marks present on their body. • They usually assist in camouflaging the fish. • During late hours of the night are these fishes usually active, performing all sorts tricks.
Conclusion • The coelacanth are indeed declared as an endangered species. • Many programmes are available, like the CITES for eg that decides what needs to be done with a captured coelacanth.
Blaxter, J.H.S, Marshall N.B, Bone Q 1995. Biology of fishes. Chapman and Hall, New York. pp323. ISBN 04127411407. Rogers, B 1986 Looking at vertebrates. Longman,USA.PP189. ISBN 0-58245086-1. Pough,FH, Heiser J.B, and Mcfarland W.N 1989 Vertebrate life. Macmillan Publishing, New York. Walker, S.M (2002) Fossil fish found live. INC./ Minneapolis,USA.pp 64. ISBN 1-57505-5368 References