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Evidences of Evolution Evolution The Fossil Record skeleton of an oviraptor The fossil record contains many welldocumented examples of the transition from one species into another, as well as the origin of new physical features. Evidence from the fossil record is unique, because it provides a time perspective for understanding the evolution of life on Earth. Preserved Hard Parts Most common types of fossils. La Brea Tar Pits, Los Angeles, Ca. - full skeletons of organisms such as the saber-toothed tiger and the wooly mammoth. Wooly Mammoth Saber-toothed Tiger Preservation of Soft Parts Preservation of an organism’s soft parts is rare because organic matter is subject to decay. In Siberia some 50 specimens of woolly mammoths and a longhorned rhinoceros were found preserved in ice with even the skin and flesh intact. Preservation in Amber Amber is a tree resin that has hardened and been preserved in the Earth’s crust for millions of years. This tree resin was generally secreted as a protective mechanism against disease and insect infestation. Often regarded as a gem, amber is actually an organic substance whose structure has changed very little over time. Petrification Molecule by molecule, woods is replaced by stable inorganic materials. This occurs when logs are buried and the organic matter is replaced by silica (quartz) slowly as the groundwater seeps through the wood. Imprints An imprint fossil forms when an object is pressed into mud, such as a leaf or insect. As it slowly dissolves, the mud surrounding it can harden and a space is left. A mold of the original object is formed, which fills with sediment and becomes a fossil. The imprint pictured is an ammonite, a extinct mollusk characterized by its flat, coiled, chambers shell. Molds and Casts Molds or casts may be left if shell material dissolves before the mud that the shells were encased in. Molds are hollows in the shape of the shell left after the shell has dissolved. Casts are the mud left from the inside of the shell after the shell has dissolved. Mold of a fossilized shell Sedimentary Rocks Older fossils of simpler life forms are found in the older layers. the upper strata generally contains fossils of younger, more complex organisms. Comparative Anatomy Organisms that have similar structures are related to each other and share a common ancestor. Vestigial Structures – structures that are no longer used by an organism but provide evidence that certain organisms were related and shared a common ancestor. Coccyx bone, tonsils, appendix, nictitating membrane humans Chicken nictitating membrane Homologous Structures Anatomical parts that are similar in origin and structure, but have different functions. Provide evidence of common ancestry. Analogous Structures Structures that have similar function but not similar underlying structure and form. The similarity is superficial and reflects an adaptation of different organisms to a similar environment. Comparative Cytology The cell is the unifying structure for all living organisms. Organelles such as the cell membrane, mitochondria, and ribosomes are structurally and functionally similar in the most divergent organisms. Comparative Biochemistry Many diverse organisms have similar DNA and protein structures, suggesting evolutionary relationship and common ancestry. Comparison of Mouse and Human DNA nucleotides Comparative Embryology Comparison of early embryonic development of among groups of organisms evidences similarities in structure and form, suggesting common ancestry. Biogeography Continental Drift --Pangea: about 200 million years ago, the continents were locked together in a single supercontinent --During the next 150 million years the supercontinent slowly separated into 7 continents. --Study of fossil locations confirms the theory that marsupials migrated by land from South America across Antarctica to Australia before those two became separate continents about 55 million years ago. --Today, most of the world’s marsupials are isolated in Australia.