Craniofacial Development in Eutherian and Metatherian Mammals

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The most significant differences between eutherian (placental) and metatherian (marsupial) mammals involve their modes of reproduction and development. Metatherians are born at a premature state relative to eutherians, and complete development while attached to the teat, nursing. The evolutionary consequences, advantages and disadvantages of these metatherian and eutherian strategies form the basis of an extensive literature. Yet, most details on the differences in morphological development are unknown. The proposed study will examine development of craniofacial features in metatherians and eutherians and is intended to form the first part of a long term study of craniofacial development in mammals. The focus of this specific project is on a detailed comparison of craniofacial development in two species, Monodelphis domestica (Didelphidae, Marsupialia), and Meoscricetus auratus (Rodentia). These are hypothesized as representative taxa for the two groups. Data on rate of development, on sequence of differentiation, and on coordination of developmental events will be collected for both species. Focus will be on the bones, muscles and nerves of the head. These data will then be applied in a preliminary manner in phylogenetic comparisons in order to assess the generality of patterns observed in these representative taxa and to form hypotheses on appropriate characters for further examination of the polarity of developmental events in placental and marsupial mammals.