Maddin & al. (2009): The anatomy and development of the claws ofXenopus laevis (Lissamphibia: Anura) reveal alternate pathways of structural evolution in the integument of tetrapods. Journal of Anatomy, no 214 (4): pp 607-19 Abstract
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Sir Walter Lawry Buller (1888): A History of the Birds of New Zealand. London excerpt from Zealand Electronic Text Centre collection