Tiktaalik
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Tiktaalik Temporal range: Late Devonian, 375 Ma |
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| Tiktaalik in the Field Museum, Chicago | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Sarcopterygii |
| Clade: | Tetrapodomorpha |
| Clade: | Stegocephalia |
| Genus: |
†Tiktaalik Daeschler, Shubin & Jenkins, 2006 |
| Type species | |
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†Tiktaalik roseae Daeschler, Shubin & Jenkins, 2006 |
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Tiktaalik /tɪkˈtɑːlᵻk/ is a monospecific genus of extinct sarcopterygian (lobe-finned fish) from the late Devonian period, about 375 Ma (million years) ago, having many features akin to those of tetrapods (four-legged animals).
Tiktaalik has a possibility of being a representative of the evolutionary transition from fish to amphibians. It is an example from several lines of ancient sarcopterygian fish developing adaptations to the oxygen-poor shallow-water habitats of its time, environmental conditions which are thought to have led to the evolution of tetrapods.
It and similar animals may possibly be the common ancestors of the broad swath of all vertebrate terrestrial fauna: amphibians, reptiles, birds, and mammals. The first well-preserved Tiktaalik fossils were found in 2004 on Ellesmere Island in Nunavut, Canada.
Tiktaalik provides insights on the features of the extinct closest relatives of the tetrapods. Unlike many previous, more fishlike transitional fossils, the "fins" of Tiktaalik have basic wrist bones and simple rays reminiscent of fingers. The homology of distal elements is uncertain; there have been suggestions that they are homologous to digits, although this is incompatible with the digital arch developmental model because digits are supposed to be postaxial structures, and only three of the (reconstructed) eight rays of Tiktaalik are postaxial.
However, the proximal series can be directly compared to the ulnare and intermedium of tetrapods. The fin was clearly weight bearing, being attached to a massive shoulder with expanded scapular and coracoid elements and attached to the body armor, large muscular scars on the ventral surface of the humerus, and highly mobile distal joints. The bones of the forefins show large muscle facets, suggesting that the fin was both muscular and had the ability to flex like a wrist joint. These wrist-like features would have helped anchor the creature to the bottom in fast moving current.
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