BSCI392
9-7-07
Fossilization and Information Loss

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We would much rather have a living organism to study than a fossil, which is incomplete and ugly by comparison. The living biota, however, gives us only the vanishingly thin time slice of the modern world. To appreciate the processes that made that biota, we have to study the imperfect remains of ancient creatures.

Definition: A fossil is any trace of an organism's body or behavior that becomes part of the rock record.

  • Two types of fossil:

    Modes of Preservation: Generally only the hard parts of organisms are preserved (although there are some exceptions). Despite what you have heard, organismal remains do not have to be altered in any way to be regarded as fossils. And yet, they often are altered by diagenesis. Major modes of preservation include:

    Becoming a fossil: From the birth of the organism to discovery by a paleontologist, fossils go through four general stages.

    Biotic stage: Birth to death. The organism grows whatever tissue is capable of being preserved then dies. It has done its part. Whether it will become part of the fossil record depends on whether its carcass can remain intact long enough to be buried. The quicker the better because.....

    Interment stage: Death to final burial. The carcass is exposed to:
    • Decomposition: destruction of soft tissues (mostly by bacteria)
    • Disassociation: hard parts become separated
    • Abrasion: surface details of hard parts lost
    • Breakage: hard parts degraded into fragments
    • Winnowing: fragments sorted by size due to moving water

    Diagenetic stage: Final burial to discovery. Once buried, the remains are officially fossils, however their existence is still perilous. Diagenesis results in:
    • Dissolution: hard parts chemically altered into soluble substances
    • Compaction: remains crushed by overlying sediment
    • Recrystallization: ground water & minerals enter, form crystals & disrupt remains

    Investigative stage: Discovery to ultimate destruction. Every day, fossils are unearthed by erosion, only quickly to be destroyed by it. To enter the fossil record, as scholars understand it, a fossil must be exhumed (usually by natural processes), discovered, and described.

    Filters and Biases

    The selection of fossils for inclusion in the fossil record is non-random. Each stage imposes its filters.