Fish with fingers?

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Abstract

Fingers and toes were long thought to be novelties associated with the invasion of land by tetrapods. The recent identification of a variety of aquatic specializations in some early tetrapods has provoked a debate on whether digits arose in primarily terrestrial or aquatic animals1,2. We recently discovered a pectoral fin of a lobe-finned fish (Fig. 1a, b) that is remarkably similar to tetrapod limbs. This discovery reveals that major tetrapod novelties are also seen in the paddles of some closely related fish and therefore need not have arisen to meet the demands of a terrestrial existence.

a, Ventral view of newly discovered right pectoral fin of a rhizodontid sarcopterygian fish (ANSP 20581); proximal humerus not exposed. Scale bar, 2 cm. Note (1) the array of jointed and branched preaxial radials; (2) common proximo-distal termination of ulnare and intermedium; (3) lack of postaxial process on the ulnare. b, Line drawing of ANSP 20581, proximal humerus reconstructed. c, Pectoral fin of the osteolepiform sarcopterygian Eusthenopteron. d, Pectoral limb of the Late Devonian tetrapod Acanthostega. Shaded elements emphasize the similarity in pattern of fin radials and digits. H, Humerus; U, ulna; r, radius; u, ulnare; i, intermedium; b, c, d are not to scale.

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References

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    Schultze, H.-P. Origins of Higher Groups of Tetrapods, 29-67 (Comstock, Ithaca, 1991).

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