ERTH 2401 Lecture : Lecture20-EvolutionofMammals.doc

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Evolution: latin word unroll", changes through time, proposed by charles darwin, on the origin of species . Lamarck"s explanation of evolution as applied to giraffes. Fossil record of mammals: transition from reptiles to mammals is poorly preserved, features such as, fur, hair, mammary glands, have poor fossil record. Evolution of mammals: origin in late triassic, earliest finds date 225-220 ma, these barely made it over the triassic extinction. Tertiary timescale: pliocene 2 mill years, miocene, oligocene, eocene, paleocene 65 mil years. Evolution of mammals: mammals remained small for about 115 ma, radiation after mass extinction of reptiles, by eocene (58 ma) most of major groups of mammals had evolved. Stages in mammalian evolution: 3 basic stages, each shows evolutionary experimentation, some lineages were successful, those radiated, others died out. Stage: early cenozoic after mass extinction, expansion of mammals into new niches left vacant by dinosaurs. A reptile adopts a sprawling gait with the limbs emerging horizontally from the body.

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