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BioMed Central, Frontiers in Zoology, 1(12), 2015

DOI: 10.1186/s12983-015-0117-x

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The phantoms of a high-seven - or - why do our thumbs stick out?

Journal article published in 2015 by Joost M. Woltering, Axel Meyer
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

The earliest tetrapods had hands and feet with up to eight digits but this number was subsequently reduced during evolution. It was assumed that lineages with more than five digits no longer exist but investigations of clawed-frogs now indicate that they posses a rudimentary or atavistic sixth digit in their hindlimb. A recent reevaluation of the stem tetrapod Ichthyostega predicts that its seven digits evolved from two different types of ancestral fin radials, pre-axial and post-axial. In this context we now ask the question, should we consider a pre-axial origin of the thumb as reason for its unique genetic signature?