What are fossils?
• Definition: The remains or trace of organisms preserved from the geologic
past........
• Criteria:
– recognizable
– organic remains or traces of activity
– must be ancient; arbitrary cut off: > 10,000 yrs.
• Body and trace fossils (ichnofossils)
• Pseudofossils -- look organic but aren't; inorganic precipitates
• Fossils = sedimentary particles or fabric
How does an organism become a fossil?
• Taphonomy
• Taphos = burial/death, nomos = laws
• Transition from the biosphere to the lithosphere
How does an organism become a fossil?
• With the people next to you discuss the following:
• Why is it unlikely that an individual organism on earth will become
a fossil?
Taphonomic Loss
• Taphonomic processes - food webs, chemical cycling, decay, scavengers,
currents, waves, etc
• Taphonomic Loss = Bias in the fossil record……….
• Taphonomic signature = gain of environmental information
– Behrensmeyer and Kidwell (1985)
Bias in the Fossil Record
• The fossil record is incomplete.
• Marine versus terrestrial realms
• Skeletonized versus soft-bodied organisms
Rules of Taphonomy
• The probability of preservation is enhanced by
1. Hard parts
2. Rapid burial - removal from TAZ
Types of Fossilization/Preservation
• Unaltered Remains
• Exceptional Preservation (soft parts)
1) freezing
2) mummification
3) amber
Unaltered Remains
• Unaltered Skeleton
• Aragonite Shells
• Bones - e.g. Rancho La Brea
• What elements of a vertebrate skeleton are most likely to be unaltered?
Permineralization
• Pores filled with silica
• Bone and wood
• Gradient from permineralization to replacement
Recrystallization/Replacement
• Shells - aragonite to calcite
• atom for atom replacement
• Silica and pyrite
Dissolution
• molds and casts
• Steinkerns (internal molds)
• shell dissolved away - mold
• space filled with sediment -cast
Carbonization
• organics preserved as carbon film
• Plants and animals
• similar process to forming coal
• Still some questions about the process