May 6, 2006 | David F. Coppedge

Fish Forsakes Fins in Favor of Arms

A crucial fossil palaeontologists are hailing as a true “missing link” in the evolutionary record has been uncovered in the arctic.  The discovery of a well preserved species of fossil fish bridges the gap between finned fish and their four legged relatives.  This croco-fish creature, documented in Nature,1 named Tiktaalik roseae has joints in its front arms and can prop itself up like a crocodile, yet has the jaw and balancing fins of a more primitive fish.  The front fins are well on their way to becoming limbs, having the internal skeletal structure of an arm, including elbows and wrists, but with fins instead of fingers.  It seems as if we have “caught” a transition in the act.  Much of the weakness of the evolutionary theory rests on these gaps that are unaccounted for with fossil records; but at last, one such transformation is right before our eyes.  The creature would represent an evolutionary window about 380 – 360 million years ago, about the time it took sea dwelling fish to differentiate into land dwelling critters.  A remark by one palaeontologist perhaps steals some of the croco-fish’s thunder when he says, “Tiktaalik was probably an unwieldy swimmer, probably living in shallow waters, only hauling itself on land temporarily to escape predators.”

1Daeschler, Edward B., Shubin, Neil H., Jenkins, Farish A. Jr., “A Devonian tetrapod-like fish and the evolution of the tetrapod body plan,” Nature, April 6, 2006: Vol. 440, p. 757-763, DOI: 10.1038/nature04639.
Shubin, Neil H., Daeschler, Edward B., Jenkins, Farish A. Jr., “The pectoral fin of Tiktaalik roseae and the origin of the tetrapod limb,” Nature, April 6, 2006: Vol. 440, p. 764-771, DOI: 10.1038/nature04637.

Why did fish, competent swimmers that they were, develop arms and legs and walk away?  This poses just a few questions to say the least.  Everyone seems to be in agreement that the fish would not immediately develop a sophisticated method of land locomotion and would thus remain rather ungainly on land for at least a few million years or so before the mechanism was refined.  Why then, would a creature at home in the sea forsake the very medium that sustained it, and venture out on land to become, pardon the pun, a true fish out of water?  As ungainly as they may have been in the water they would have been even more so out of the water, therefore how is this to be considered favorable?  Natural Selection, Darwin’s brainchild would seem to weed out these unfavorable mutations as opposed to propagating them.  Easy for us to come in a posteriori and tie the loose ends together; but to be completely honest, the fish did not decide it would be beneficial to walk on land and then determine to sprout arms.  I thought the Lamarckian ideas were thrown out years ago? How then do these undertones manage to still get incorporated into modern thought?
Lydia Bye

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Categories: Fossils

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