Taphonomy I: Properties and Habitats of Good Fossil Makers

Taphonomy: The realm of paleontology dedicated to the study of the processes by which an organism becomes part of the fossil record. Yields an understanding of the filters and biases of the fossil record.

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 can be 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:

Diagenetic stage: Final burial to discovery. Once buried, the remains are officially fossils, however their existence is still perilous. Diagenesis results in:

Field excavation from Bureau of Land Management
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.

The selection of fossils for inclusion in the fossil record is non-random. Each stage imposes filters and biases. These will be explored in a later lecture. For now, we concentrate on the most fundamental filter: Not all clades of organisms produce preservable hard parts. Although soft bodied organisms can produce fossils under special (konservat-lagersätten) situations to be considered later. a first-order approximation is that only creatures that make hard parts during life have any hope of becoming fossils. Only a short list of suitable hard substances are produced by organisms.

Main hard substances found in organisms:

Aragonite (CaCO3) from Wikipedia
  • Calcite and/or aragonite - CaCO3 (calcareous hard parts dominate the fossil record).

    Calcareous skeletons are thought to have originated at least twenty times in eukaryote evolution. Also the first biomineral skeletons known, dating to 750 m.a. Typically secreted extracellularly. The abundance of independent origins suggests the exaptation (coopting) of an underlying biochemical mechanism present in soft-bodied precursors such as:

    Phylogeny of skeleton-forming eukaryotes from Knoll, 2003.

    List of some of the major clades producing common body fossils:

    (Classifications used here largerly follow these on the UMCP website)

    Organisms with silicious skeletons

    Organisms with calcareous skeletons

    Organisms with phosphatic skeletons

    Organisms with "tough tissues"