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Post by 1dave on Oct 26, 2016 20:19:06 GMT -5
I'm in the process of re-doing this thread. It helps me bring order out of otherwise chaos in our history. I still need to clarify the "Post Mortems" at the end of each period to clarify what brought it to an end. |
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Post by 1dave on Oct 27, 2016 7:10:26 GMT -5
Organisms are only rarely preserved as fossils in the best of circumstances, and only a fraction of such fossils have been discovered. This is illustrated by the fact that the number of species known through the fossil record is less than 5% of the number of known living species, suggesting that the number of species known through fossils must be far less than 1% of all the species that have ever lived.[27] Because of the specialized and rare circumstances required for a biological structure to fossilize, only a small percentage of life-forms can be expected to be represented in discoveries, and each discovery represents only a snapshot of the process of evolution. The transition itself can only be illustrated and corroborated by transitional fossils, which will never demonstrate an exact half-way point.[28] The fossil record is heavily slanted toward organisms with hard parts, leaving most groups of soft-bodied organisms with little to no role.[27] It is replete with the mollusks, the vertebrates, the echinoderms, the brachiopods and some groups of arthropods.[29] 
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