Tiktaalik is an extinct sarcopterygian ‘fishapod’ which evolved during the late Devonian period (375 ma) and it is regarded as an important transitional lifeform.
Tiktaalik has an anatomy that displays a number of features that indicate a clear linkage between fish and tetrapoda (land vertebrates). These anatomical features point to how life may have moved from water onto land and Tiktaalik is thought to have been among the first vertebrates to cross this margin.
The morphology of interest includes a dorso-ventrally flattened head with raised dorso-anterior eyes - this meant that Tiktaalik would have been able to move just below the water surface, in much the same way as modern crocodiles, able to approach banks and margins. A muscular pectoral girdle and freely moving neck also suggest that Tiktaalik would have been able to prop itself up and to turn its head independently - enabling it to scan surface environments. These features indicate that Tiktaalik may have been a very effective tidal margin predator.
Tiktaalik also has spiracles on top of its head which is suggestive of lung development as well as gill breathing ability. This would have been useful in the warming shallow waters of the time that may have been low in oxygen content.
Most distinctively, Tiktaalik has lobed limbs that end in squat fins. These lobe-fins have internal bone structures that correlate to the arm and leg bones of all land vertebrates.
It is unlikely that we are the direct descendants of Tiktaalik but rather a convergent evolutionary branch - meaning that different lineages of vertebrate probably made independent transitions onto land - possibly at even earlier times. Tiktaalik is just a perfect example of such an evolutionary step and speculation on its existence led to it being discovered on Ellesmere Island in 2004.
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