Molecules, Morphology, and the Evolutionary Radiation of Placental Mammals

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Springer9903810Living placental mammals comprise a group of approximately 4,000 species that are classified into 18 different orders (e.g., rodents, primates, rabbits and pikas, elephants, sea cows). Resolving evolutionary relationships among these orders has proved difficult. Fundamental questions concerning the evolutionary history of mammals remain unsettled. How did the breakup of ancient supercontinents affect the evolutionaryhistory of mammals? How did the extinction of dinosaurs and other large reptiles 65 million years ago influence the evolution of the major groups of mammals? How frequently have different kinds of adaptations (e.g., echolocation systems for navigation during flight) evolved among mammals? One approach to reconstruct evolutionary genealogy is to use DNA sequences. In our study, we will obtain DNA sequences for seven different genes from 97 placental mammals. The mammals that were chosen for this study are representative of all major groups. In addition to reconstructing anevolutionary genealogy, we will estimate divergence times among mammalianorders using a molecular clock. The evolutionary history that we reconstruct using molecules will provide a framework for evaluating how continental breakup and mass extinction have influenced mammalian evolution. We will also examine the origins of mammalian adaptations in light of the evolutionary tree that we obtain with DNA sequences.