Editor's Summary

24 May 2007

Limbering up

The limbs of tetrapods (land-living vertebrates) are usually thought of as evolutionary innovations unique to that group. Now a study of Hox gene expression during development of the fins of a 'living fossil', the paddlefish Polyodon spathula, shows that patterns of gene expression and regulation thought characteristic of the tetrapod limb are found in the fins of basal ray-finned fish. The paddlefish is one of the few relics of a type of bony fish common in the seas more than 250 million years ago. The work shows that some aspects of limb development are primitive and held in common by all bony fish — but have been lost in highly evolved fishes such as the zebra fish. These results are in accord with recent new fossil discoveries such as Tiktaalik, a fish that shows skeletal progression from fish to tetrapod.

Letter: An autopodial-like pattern of Hox expression in the fins of a basal actinopterygian fish

Marcus C. Davis, Randall D. Dahn & Neil H. Shubin

doi:10.1038/nature05838

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