When life moved onto landThe Devonian is usually nicknamed the age of fishes, for the plentiful foss

When life moved onto landThe Devonian is usually nicknamed the age of fishes, for the plentiful fossils that testify to a large radiation in species, both bony and cartilaginous, during this era. It also marks the period when certain fishes first evolved the mechanisms that allowed vertebrates to exploit terrestrial ecosystems, mainly involving the transformation of fins into limbs.Tiktaalik, a 417-350 million year old fossil organism pictured here, is the best missing link found so far, revealing this important transition in the history of life that paved the way for our evolution. Its discovery also proved the existence of a transitional shallow water form that proponents of intelligent design had said constituted a major gap in life’s story.First discovered in 2004 in Ellesmere Island, these fish were fierce predators that grew up to 2.5 metres long, with limbs capable of use on land or in water. Named ‘a large shallow water fish’ in Inuktikuk (the Inuit language), their skull, neck and ribs are similar to those of early amphibious animals called tetrapods, and jaws, fins and scales like a fish’s.In the Devonian, northern Canada was on the equator, and Tiktaalik had both gills and lungs and lived in fresh water rivers. A recently published study of the hind limbs shows that like the arms, they could have supported the animal in full gravity, implying that it exploited both sets of ecosystems. It shows that these early organisms had three joints corresponding to shoulder, elbow and wrist, and that front and hind limbs were equally strong, a trait previously thought to have originated in later tetrapods.LozImage credit: Ghedoghedohttp://www.theguardian.com/science/2014/jan/13/tiktaalik-fossil-fish-four-legged-land-animalhttp://www.theguardian.com/science/2006/apr/06/evolution.fossilshttp://tiktaalik.uchicago.edu/Original paper, paywall access: http://www.pnas.org/content/early/2014/01/08/1322559111.abstract -- source link

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