How to Find a Late Devonian Tetrapod

Discovering a fossil specimen of a tetrapod from the Late Devonian Epoch is not a matter of chance. Evidence representing this critical stage in the transition of vertebrates from water to land is rare, and most of it is found in far-flung locations. A survey of the 13 fossil sites currently known to contain tetrapods from the Late Devonian reveals that more than half of the 16 recognized genera of such animals are known from scant evidence consisting of little more than a single skeletal element such as a jaw or limb bone. The sites are scattered around the world, mostly in remote locations in the Northern Hemisphere. In other words, Late Devonian fossil sites are scarce and, with only a few exceptions, difficult to get to. These logistical issues complicate exploration for early tetrapod fossils.

Many paleontologists hoping to find tetrapods have returned to well-established fossil deposits such as those in eastern Greenland. A more risky and daring strategy is to find a site that has never yielded tetrapods or near-tetrapods before. Ted Daeschler and Neil Shubin took the latter approach when they decided to explore Late Devonian geological formations in Nunavut, Canada, that had formed in shallow-water habitats that could have been exploited by early, transitional fish-tetrapods. Their gamble paid off with the discovery of Tiktaalik, a lobe-finned fish that probably lived in the water but whose anatomical features would have allowed it to crawl onto land from time to time.

The recognition of Tiktaalik was preceded by four years of exploring for fossils in the Canadian Arctic, where the summers are short and the sun shines for nearly 24 hours a day. The Tiktaalik site is located in a valley of the remote Ellesmere Island, about 600 miles north of the Arctic Circle in the Nunavut Territory. The expeditions have each included between six and eight scientists and students.

In 2000, tantalizing fossil fragments found at the site gave the scientists hope that they might be onto something related to the fish-tetrapod transition. It became clear to them that the site had once been subtropical

Tiktaalik was discovered in the Canadian Arctic, where the season for digging fossils is short because of cold weather.

in climate. It consisted of shallow-water stream deposits—an ideal habitat for the first tetrapods. Daeschler, Shubin, and other team members returned to the site several times, continuing their search until, in 2004, they recovered several well-preserved specimens of Tiktaalik. The fossils were collected while still mostly encased in rocks and were protected by plaster jackets. The protected fossils then were lifted by helicopter out of the site to begin their 3,000-mile journey back to the United States for complete preparation and study. Once research has been completed, the specimens will be returned to a Canadian scientific institution for permanent keeping.

What the team found after studying the fossil-bearing rocks was startling. No less than three partial specimens of Tiktaalik eventually emerged



as laboratory preparators carefully cleared away the rock matrix from the bones. Nearly two years later, a clear picture of Tiktaalik took shape, and Daeschler, Shubin, and their colleague Farish Jenkins published the details of their discovery in the journal Nature in April 2006.

What, you may ask, is the significance of the discovery's name? The scientists borrowed the name Tiktaalik from the language of the residents in the region of the Canadian Arctic where the fossil was found. The name, which is pronounced tick-TAH-lick, is an Inuktikuk word for a large, shallow-water fish.

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of reptiles and mammals, two groups that, in turn, would make themselves masters over the great variety of life-forms.

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