Devonian missing link

Article By:

Clack, Jennifer A. University Museum of Zoology, Cambridge, United Kingdom.

Last reviewed:2008

DOI:https://doi.org/10.1036/1097-8542.YB081210

A key stage in the evolutionary history of life on Earth is the transition between fish with fins and animals with limbs and digits (such animals are known as tetrapods). This event is thought to have happened between about 370 and 360 million years ago, in the Devonian Period. In 1999, a team of paleontologists mounted their first expedition to Ellesmere Island in the Canadian territory of Nunavut in the Arctic Circle, with the hope of finding fossils that represent this transition. Although this locality had never before been visited by vertebrate paleontologists, the team's visit was an informed guess or prediction that the geological age and type of sediments there were just right for potentially finding relevant material. The sediments were formed in meandering streams and river estuaries in the early part of the Late Devonian about 370 million years ago. Over a series of four expeditions, the collective hunch paid off. After three seasons, the team found a rich seam of vertebrate-bearing rocks that yielded an array of many different kinds of fishes, including some lower jaws and a snout of a previously unknown form but which looked tantalizingly like a transitional form. In the fourth season, they discovered almost complete skeletons and many isolated parts of this creature, which indeed proved to be a spectacular and important new addition to the story of the origin of tetrapods. They called it Tiktaalik roseae: Tiktaalik is the local Inuktitut name for a large freshwater fish seen in the shallows, and roseae honors the benefactor who provided much of the expeditionary funds.

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