Description Tiktaalik

restoration

tiktaalik provides insights on features of extinct closest relatives of tetrapods. unlike many previous, more fishlike transitional fossils, fins of tiktaalik have basic wrist bones , simple rays reminiscent of fingers. homology of distal elements uncertain; there have been suggestions homologous digits, although incompatible digital arch developmental model because digits supposed postaxial structures, , 3 of (reconstructed) 8 rays of tiktaalik postaxial.

however, proximal series can directly compared ulnare , intermedium of tetrapods. fin weight bearing, being attached massive shoulder expanded scapular , coracoid elements , attached body armor, large muscular scars on ventral surface of humerus, , highly mobile distal joints. bones of forefins show large muscle facets, suggesting fin both muscular , had ability flex wrist joint. these wrist-like features have helped anchor creature bottom in fast moving current.

skull showing spiracle holes above eyes



the alligator gar extant fish bears resemblance tiktaalik.

also notable spiracles on top of head, suggest creature had primitive lungs gills. attribute have been useful in shallow water, higher water temperature lower oxygen content. development may have led evolution of more robust ribcage, key evolutionary trait of land-living creatures. more robust ribcage of tiktaalik have helped support animal’s body time ventured outside aquatic habitat. tiktaalik lacked characteristic fishes have—bony plates in gill area restrict lateral head movement. makes tiktaalik earliest known fish have neck, pectoral girdle separate skull. give creature more freedom in hunting prey either on land or in shallows.

tiktaalik compared gars (esp. atractosteus spatula, alligator gar) of lepisosteidae family, whom shares number of characteristics:

diamond-shaped scale patterns common crossopterygii class (in both species scales rhombic, overlapping , tuberculated);
teeth structured in 2 rows;
both internal , external nostrils;
tubular , streamlined body;
absence of anterior dorsal fin;
broad, dorsoventrally compressed skull;
paired frontal bones;
marginal nares;
subterminal mouth;
lung-like organ.




^ laurin m (2006). scanty evidence , changing opinions evolving appendages . zoologica scripta. 35 (6): 667–668. doi:10.1111/zsc.2006.35.issue-6. 
^ cite error: named reference shubin 2008 invoked never defined (see page).
^ holmes, bob (2007). meet ancestor, fish crawled . new scientist. retrieved 2007-02-07. 
^ cite error: named reference scientificamerican invoked never defined (see page).
^ spitzer, mark (2010). season of gar: adventures in pursuit of america s misunderstood fish. university of arkansas press. pp. 65–66. isbn 978-1-55728-929-2.