| Coelacanth Fossil range: Devonian–Cretaceous (but extant) |
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| specimen of Latimeria chalumnae in the Natural History Museum, Vienna, Austria (length: 170 cm - weight: 60 kg). This specimen was caught on 18 October 1974, next to Salimani/Selimani (Grand Comoro, Comoro Islands) 11°48′40.7″S 43°16′3.3″E / 11.811306°S 43.267583°E. | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Sarcopterygii |
| Subclass: | Actinistia |
| Infraclass: | Coelacanthimorpha |
| Order: | Coelacanthiformes Berg, 1937 |
| Families | |
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See text. |
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Coelacanth (pronounced /ˈsiːləkænθ/, adaptation of Modern Latin Cœlacanthus "hollow spine", from Greek κοῖλ-ος koilos "hollow" + ἄκανθ-α akantha "spine", referring to the hollow spines of the fins) is the common name for an order of fish that includes the oldest living lineage of gnathostomata known to date.
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The coelacanths, which are related to lungfishes and tetrapods, were believed to have been extinct since the end of the Cretaceous period. They were considered the "missing link" between the fish and the tetrapods until the first Latimeria specimen was found off the east coast of South Africa, off the Chalumna River in 1938. They are, therefore, a Lazarus taxon. Since 1938, Latimeria chalumnae have been found in the Comoros, Kenya, Tanzania, Mozambique, Madagascar, and in iSimangaliso Wetland Park, Kwazulu-Natal in South Africa. The second extant species, L. menadoensis, was described from Sulawesi, Indonesia in 1999 by Pouyaud et al.[1] based on a specimen discovered by Erdmann in 1998[2] and deposited in Indonesian Institute of Sciences (LIPI). The first specimen of this species was only photographed at a local market by Arnaz and Mark Erdmann before being bought by a shopper. The coelacanth has no real commercial value, apart from being coveted by museums and private collectors. As a food fish the coelacanth is almost worthless as its tissues exude oils even when dead, imparting the flesh with a foul flavor.[3]
They first appeared in the fossil record in the Middle Devonian.[4] Prehistoric species of coelacanth lived in many bodies of water in Late Paleozoic and Mesozoic times.
Coelacanths are lobe-finned fish with the pectoral and anal fins on fleshy stalks supported by bones, and the tail or caudal fin diphycercal (divided into three lobes), the middle one of which also includes a continuation of the notochord. Coelacanths have modified cosmoid scales, which are thinner than true cosmoid scales. Coelacanths also have a special electroreceptive device called a rostral organ in the front of the skull, which probably helps in prey detection. The small device also could help the balance of the fish, as electrolocation could be a factor in the way this fish moves.
This fish has some unique traits among vertebrates:[5]
Although now represented by only two known living species, as a group the coelacanths were once very successful with many genera and species that left an abundant fossil record from the Devonian to the end of the Cretaceous period, at which point they apparently suffered a nearly complete extinction. Before the living specimens were discovered, it was believed by some that the coelacanth was a "missing link" between the fish and the tetrapods. It is often claimed that the coelacanth has remained unchanged for millions of years, but, in fact, the living species and even genus are unknown from the fossil record. The most likely reason for the gap is the taxon having become extinct in shallow waters. Deep-water fossils are only rarely lifted to levels where paleontologists can recover them, making most deep-water taxa disappear from the fossil record.
The fossils of the coelacanth are believed to be indicative of the order's place as a transitional evolutionary link due to the presence of leg-like structures. Extant specimens of two species of the genus Latimeria have been discovered, allowing study of evolutionary changes within the Coelacanthiforme order. [6]
Subclass Coelacanthimorpha (Actinistia) are sometimes used to designate the group of Sarcopterygian fish that contains the Coelacanthiformes. The following is a classification of known coelacanth genera and families:[7]
Class Sarcopterygii
Subclass Coelacanthimorpha
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