Biology 1001A Chapter Notes - Chapter Cycle 9: Parallel Evolution, Gastrolith, Polyphyly
4 Apr 2017
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Document Summary
Sediments found in any one place form distinctive strata (layers) that usually differ in colour, mineral composition, particle size, and thickness. But geologic processes cause strata to be uplifted, warped, or even inverted. Because each stratum was formed at a specific time, the sequence of fossils from lowest (oldest) to highest (newest) strata reveals their relative ages. Dissolved minerals entered the spaces within the bones and then solidified. Preserved in amber (tree resin), show fine details of the organisms. These may have been compressed shortly after death, so three-dimensional analysis may be difficult. Footprints may be fossilized when an animal walks across mud. Droppings (coprolites) and gastroliths, stones in the stomach used to grind food. Fossil record is incomplete because few organisms fossilize completely, because some organisms are more likely to fossilize than others, and because natural processes destroy many fossils. Stromatolite is a laminated usually mounded sedimentary fossil formed from layers of cyanobacteria, calcium carbonate, and trapped sediment.
