Acanthostega BW

Reconstruction of Acanthostega gunnari

Polydactyly in early tetrapod aquatic animals was not polydactyly in the common sense, i.e., it was not an anomaly in the sense it was not a condition of having more than the typical number of digits for a given taxon.[1]

Acanthostega had eight digits, while the more derived Ichthyostega had seven digits. Following this trend, the yet-more derived Tulerpeton had six.[1]

The increasing number of such discoveries in paleontology has led to the challenging of the hypothesis that pentadactyly, as displayed by most modern tetrapods, is plesiomorphic. The number of digits may have reduced in amphibians and reptiles independently.[1]


  1. ^ a b c Evolutionary developmental biology, by Brian Keith Hall, 1998, ISBN 0412785803, p. 262
  • Coates, M.I. and Clack, J.A. (1990) Polydactyly in the earliest known tetrapod limbs. Nature, 347, pp.66-69.
Mantell's Iguanodon restoration

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