Reconstructing the evolution of viviparity and placentation

A recent paper in J. theor. Biol. has challenged the proposed application of punctuated equilibrium models to the evolution of reptilian viviparity and placentation. While clarifying some aspects of the models, the paper's criticisms reflect misinterpretations of the literature and an unnecessary reluctance to apply punctuationist concepts to extant taxa. The punctuated equilibrium model retains potential for clarification of the patterns of stasis and episodic change that may well have characterized squamate reproductive history. (C) 1998 Academic Press Limited.