Evolution of placental specializations in viviparous African and South American lizards

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Abstract
Phylogenetic information offers an important resource in analyses of reproductive diversity, including interpretations of fetal membrane evolution. In this paper, we draw upon ongoing studies of South American and African lizards to consider the value of combining phylogenetic and reproductive evidence in the construction of evolutionary interpretations. South American lizards of the genusMabuyaexhibit several reproductive specializations that are convergent on those of eutherian mammals, including viviparity, long gestation periods, ovulation of tiny eggs, and placental supply of the nutrients for development. Studies of placental morphology and development indicate that New WorldMabuyashare several other derived features, including chorionic areolae and a “Type IV” epitheliochorial placenta with a villous, mesometrial placentome. Some characteristics of these lizards are shared by two African skinks,M. ivensiiandEumecia anchietae, including minuscule eggs, placentotrophy, an absorptive chorioallantois, and features of the yolk sac. Available evidence is consistent with two explanations: (1) placentotrophy originated in Africa, predating a trans‐Atlantic colonization byMabuyaof the New World; and (2) placentotrophy arose two or three separate times among these closely related skinks. As illustrated by analysis of these animals, not only can data on fetal membrane morphology yield phylogenetic information, but phylogenetic evidence in turn provides a valuable way to reconstruct the evolution of fetal membranes in a biogeographic context. When appropriately interpreted, morphological and phylogenetic evidence can be combined to yield robust evolutionary conclusions that avoid the pitfalls of circular reasoning.J. Exp. Zool. 299A:33–47, 2003.