May 3, 2006 | David F. Coppedge

Tiktaalik: Evolution’s Newest Link in the Chain

Researchers have recently discovered a fossil on Ellesmere Island, located in the Canadian Arctic.  The creature is characteristic of tetrapods, four-legged organisms, and possesses a flattened body, fins, scales, ribs, and a neck.  James Owen (National Geographic News1) considers the species, Tiktaalik roseae, to be the connection between aquatic and land animals and prehistoric predecessor of the human population:

Researchers say the fish shows how fins on freshwater species first began transforming into limbs some 380 million years ago.  The change was a huge evolutionary step that opened the way for vertebrates—animals with backbones—to emerge from the water.  “This animal represents the transition from water to land—the part of history that includes ourselves,” said paleontologist Neil Shubin of the University of Chicago.  Tiktaalik could become an icon of evolution in action, write paleontologists Per Ahlberg of Sweden’s Uppsala University and Jennifer A. Clack of the University of Cambridge in the United Kingdom in an accompanying commentary.  The paleontologists say the new fish form goes a long way toward filling the evolutionary gap between fish and the earliest amphibians.  “Our remote ancestors were large, flattish, predatory fishes,” they write.  “Strong limblike pectoral fins enabled them to haul themselves out of the water.”  Evolutionary scientists agree that all four-limbed land vertebrates, including dinosaurs and mammals, are descended from lobe-fins, a group of primitive fishes with fins suggesting limbs.   (Emphasis added in all quotes.)

1James Owen, “Fossil Fish With ‘Limbs’ Is Missing Link, Study Says,” National Geographic News. 04/05/2006.
Shubin et al., “The pectoral fin of Tiktaalik roseae and the origin of the tetrapod limb,” Nature 440, 764-771 (6 April 2006) | doi:10.1038/nature04637.
John Roach, “Fins to Limbs: New Fossil Gives Evolution Insight,” National Geographic News, 04/01/2004.
“Newly Found Species Fills Evolutionary Gap Between Fish And Land Animals,” Science Daily, 04/06/2006.

Tiktaalik roseae is an important discovery for scientists and media alike.  However, evidence for a transition from water to land does not authenticate the so-called link between humans and their aquatic associates.  “The previously unknown creature is the closest known fish ancestor of land vertebrates,” said Shubin.  If researchers are so confident with Tiktaalik’s ability to hoist itself onto land and evolve into a land-dwelling organism, why have we discovered so few fossils that prove the existence of missing links and their transitions from water to land?  Ted Daeschler (Academy of Natural Sciences in Philadelphia) said, “The transition wasn’t all or nothing.  It’s not that some animals were thrown on land.  There were certainly other functions intermediate.”  What exactly were those functions?  Also, how were the functions intermediate determined based upon evidence of fossils that have not been discovered?  How can researchers allude to the existence of numerous transitional species with a lack of data necessary to substantiate their conclusions?  Perhaps, we should answer these questions before we hoist ourselves onto the idea of human-fish relations.
– Courtney N.

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Categories: Fossils

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