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Earth Sciences
ERTH 2401
Claudia Schroder- Adams

Lecture 20 Evolution of MammalsEvolution Latin word unroll Changes through time Proposed by Charles Darwin On the Origin of SpeciesPrincipal of Natural Selection Individuals compete for space food and other resources Individuals produce more offsprings than can survive Individuals vary in their traitsDue to limited resources only some offsprings will survive Nature chooses variation in traits which assure survival and passes them onLamarcks explanation of evolution as applied to giraffes Older giraffes stretch to reach leaves subsequent generations retain this characteristic to reach foodDid Mammals have an advantage over Dinosaurs Smaller size Retaining more options such as Flexibility to swim climb dig run jump Larger species had to specialize harder to adapt to a changing environmentMammal Diversity Less diverse than Fish Reptiles Birds Total number of vertebrates dwarfed by numbers of animals such as insects or even mollusksFossil record of mammals Transition from reptiles to mammals is poorly preserved Features such as Fur Hair Mammary glands Have poor fossil recordEvolution of Mammals Origin in Late Triassic Earliest finds date 225220 Ma These barely made it over the Triassic extinctionTertiary Timescale Pliocene 2 Mill years Miocene Oligocene Eocene Paleocene 65 Mil yearsEvolution 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 evolvedStages in Mammalian Evolution
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