Dictionary Definition

crossopterygian n : any fish of the order Crossopterygii; most known only in fossil form [syn: lobefin, lobe-finned fish]

Extensive Definition

Sarcopterygii (from Greek sarx, flesh, and pteryx, fin) is traditionally the class of lobe-finned fishes, consisting of lungfish and coelacanths.

Characteristics

Sarcopterygians are bony fish with lobed paired fins, which are joined to the body by a single bone . These fins evolved into legs of the first tetrapod land vertebrates, amphibians. They also possess two dorsal fins with separate bases, as opposed to the single dorsal fin of actinopterygians (ray-finned fishes). The braincase of sarcoptergygians primitively has a hinge line, but this is lost in tetrapods and lungfish. Many early sarcopts have a symmetrical tail.
Most taxonomists who subscribe to the cladistic approach include the grouping Tetrapoda within this group, which in turns consists of all species of four-limbed vertebrates. The fin-limbs of sarcopterygiians show such a strong similarity to the expected ancestral form of tetrapod limbs that they have been universally considered the direct ancestors of tetrapods in the scientific literature.

Evolution of Sarcopterygii

Sarcopterygians belong to Osteichthyes group or bony fishes, characterized by their bony skeleton instead of cartilage. The oldest Sarcopterygians were found in the Uppermost Silurian. The first Sarcopterygian closely resembled Acanthodians. The Sarcopterygians closest relatives were the Actinopterygiansray-finned fishes. Sarcopterygians probably evolved in the oceans, but they later came into freshwater habitats to avoid the predatory placoderms — which were dominant in the Early–Middle Devonian seas.
As Sarcopterygians evolve in the Early Devonian, the line splits into two main lineages — the Coelacanths, and the Rhipidistia. The Coelacanths appeared in the Early Devonian, and stayed in the oceans; the coelacanths' heyday was the Late Devonian and Carboniferous, as they were more common during those periods than in any other period in the Phanerozoic. Coelacanths still live today in the oceans. Rhipidistians appeared about the same time as the Coelacanths, but unlike them, Rhipidistians left the ocean world and migrated into the freshwater habitats, their ancestors probably lived in the oceans near the river mouths (estuaries). The Rhipidistians in turn split into two major groups — the lungfishes, and the tetrapodomorphs. The lungfishes' greatest diversity was in the Triassic Period, but today, there are fewer than a dozen genera left. The lungfishes evolved the first proto-lungs and proto-limbs. The lungfishes, ancient and modern, used their stubby fins (proto-limbs) to walk on land and find new water if their waterhole was depleted, and used their lungs to breathe air and get sufficient oxygen.
The tetrapodomorphs have the same identical anatomy as the lungfishes, who were their closest kin, but the tetrapodomorphs appear to have stayed in water a little longer until the Late Devonian. Tetrapods — four legged vertebrates were the terapodomorphs' descendants. Tetrapods appeared in the Late Devonian epoch.
Non-tetrapod sarcopterygians continued to towards the end of Paleozoic Era. They suffered heavy losses during the Permian-Triassic extinction event.

Taxonomy and Phylogeny

See also

References

crossopterygian in Bulgarian: Ръкоперки
crossopterygian in Catalan: Sarcopterigi
crossopterygian in Czech: Nozdratí
crossopterygian in German: Fleischflosser
crossopterygian in Estonian: Sagaruimsed
crossopterygian in Spanish: Sarcopterygii
crossopterygian in Esperanto: Sarkopterigo
crossopterygian in French: Sarcopterygii
crossopterygian in Italian: Sarcopterygii
crossopterygian in Hebrew: בעלי סנפירים בשרניים
crossopterygian in Latin: Sarcopterygii
crossopterygian in Lithuanian: Mėsingapelekės žuvys
crossopterygian in Hungarian: Bojtosúszójú halak és tüdőshalak
crossopterygian in Dutch: Kwastvinnigen
crossopterygian in Japanese: 肉鰭綱
crossopterygian in Norwegian Nynorsk: Kjøtfinnefisk
crossopterygian in Occitan (post 1500): Sarcopterygii
crossopterygian in Polish: Mięśniopłetwe
crossopterygian in Portuguese: Sarcopterygii
crossopterygian in Quechua: Aycha wayt'ana
crossopterygian in Russian: Лопастепёрые рыбы
crossopterygian in Simple English: Sarcopterygii
crossopterygian in Slovak: Násadcoplutvovce
crossopterygian in Serbian: Саркоптеригије
crossopterygian in Finnish: Varsieväiset
crossopterygian in Swedish: Lobfeniga fiskar
crossopterygian in Vietnamese: Lớp Cá vây thùy
crossopterygian in Turkish: Et yüzgeçliler
crossopterygian in Ukrainian: Лопастепері
crossopterygian in Zeeuws: Kwastvinnigen
crossopterygian in Chinese: 肉鳍鱼类
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