Quiz_2_Condensed_Notes_F08

Quiz_2_Condensed_Notes_F08 - LECTURE 10: EVIDENCE FOR...

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LECTURE 10: EVIDENCE FOR EVOLUTION There are many lines of evidence that support the idea that organic evolution actually occurs. For example, the fact that some organisms are well-adapted to the particular environment in which they live is consistent with natural selection. Commonalities in livings, like similar cell, embryonic, and skeletal structures, would also be expected if life forms share a common ancestor. Vestigal organs and bones that serve no function can be explained by evolution from an ancestor that had the same, but functioning, organ or bone. Finally, systematic changes in fossils are sometimes preserved, providing a record of directional change in species. LECTURE 10: FOSSILIZATION AND EARLY METAZOANS Fossils are any evidence of past life. Body fossils are the actual remains of hard or soft tissues of the organism itself. Trace fossils are evidence of the activity of ancient life such as footprints, burrows, coprolites, and gastroliths. Fossils can be made by: 1) total preservation of the organism (i.e., an organism trapped in ice or amber), 2) replacement of organic materials by minerals (i.e., petrified wood), 3) impressions , 4) compressions (a carbonized film), 5) molds, and 6) casts. There are two types of molds. An external mold forms when a shell that is surrounded by sediment dissolves and leaves behind a void space that preserves the external features of the shell. An internal mold forms when a shell that is filled-in with sediment dissolves and leaves behind a three-dimensional object that preserves the internal features of the shell. A cast forms when an external mold is later filled in with sediment, creating a three-dimensional object that preserves the external features of the shell. Fossil collections may be biased (may not accurately reflect the types and abundances of plants and animals living in the past) by: 1) the lack of preservation of some organisms in the ancient ecosystem, 2) the collection of only certain types of fossils, and 3) the improper identification of fossils. Two fossil deposits, the Ediacara deposit and the Burgess Shale (discussed below) are particularly unbiased with respect to preservation and reveal an amazing diversity of life. Metazoans are many-celled animals. Some of the oldest fossil metazoans are found in the Ediacara deposit in southwestern Australia. These animals lived in a shallow marine environment at the end of the Precambrian time period. They are extremely well- preserved, which suggests that the organisms were buried rapidly. The fossils in the Ediacara deposit include soft-bodied organisms like jelly fish and worms that were passive filter feeders. The Ediacara fossil deposit represents a fairly primitive ecosystem. Some of the Ediacara animals had bizarre body plans, unlike anything living today.
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Quiz_2_Condensed_Notes_F08 - LECTURE 10: EVIDENCE FOR...

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