Fossils

TYPES OF FOSSILS

• BODY FOSSILS - USUALLY HARD SKELETAL MATERIAL (SHELLS, BONES, TEETH); RARELY SOFT TISSUE (DUE TO FREEZING OR MUMMIFICATION)
• TRACE FOSSILS - TRACKS & TRAILS, BURROWS, BORINGS, NESTS, OR ANY OTHER INDICATION OF ACTIVITY BY ORGANISMS
  • useful for deducing environments of deposition, & life style of organisms
  • coprolites - fossilized feces

PRESERVATION

• SURPRISING ANYTHING IS EVER PRESERVED
  • organic materials are easily destroyed & rapidly scavenged
• HARD PARTS HAVE A BETTER CHANCE OF PRESERVATION
  • soft tissues rarely are
• RAPID BURIAL INCREASES CHANCES THAT SOMETHING WILL BE PRESERVED
  • marine invertebrates with shells stand the best chance of fossilization
  • soft-bodied terrestrial organisms have the least
  • more complete record for marine organisms with hard parts
  • less complete record for soft-bodied terrestrial organisms

TYPES OF FOSSILIZATION

• UNALTERED BODY FOSSILS
  • soft tissue can be preserved in amber or tar, or by mummification or freezing
  • hard parts may be preserved without change - usually shells (calcium carbonate & silica), bone/teeth (calcium phosphate), or pollen & spores
• ALTERED BODY FOSSILS
  • Carbonization: soft tissues preserved as thin carbon films
  • Permineralization: porous material filled with secondary minerals
  • Recrystallization: conversion of a mineral polymorph to another
    • E.G. ARAGONITE -> CALCITE, OR OPAL -> QUARTZ
  • Replacement: dissolution of original material, precipitation of new mineral, equal in volume to that dissolved
    • CAN PRESERVE FINEST DETAILS
  • Petrification: replacement or permineralization of wood
• MOLDS (DISSOLUTION OF SHELL) & CASTS (FILLING OF MOLD)
• TRACE FOSSILS - SEE ABOVE

USES OF FOSSILS

• BIOSTRAGRAPHY - stratigraphic correlation
• PALEOECOLOGY - relationships of fossil organisms to each other & to environment
• PALEOBIOGEOGRAPHY - restriction of fossils to particular geographic areas

Study Questions

1. Summarize the differences between trace & body fossils & give examples of each.

2. What factors control whether any fossil is preserved?

3. Summarize the types of fossilization.

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