Lab 6 Slides Flashcards
(26 cards)
What is a Fossil?
Fossils are prehistoric remains or traces of life, which have been preserved by natural causes in the Earth’s crust
Taphonomy
The study of processes responsible for any organism becoming part of the fossil record and how these processes influence information in the fossil record.
What makes an organism likely to become a fossil?
- Have preservable parts
- Be buried by sediment
- Escape physical, chemical, and biological destruction after burial
Preservable Parts
Hard parts (bones, shells, teeth, wood) have a much better chance at being preserved than soft parts (muscle, skin, internal organs)
Being buried by sediment
Burial protects the organism from decay
Escape physical, chemical, and biological destruction after burial
The remains of organisms could be destroyed by burrowing (bioturbation), dissolution, metamorphism, or erosion
Bioturbation
Burrowing
Types of Preservation
Three main types:
* Preservation of unaltered parts
* Chemical alteration of hard parts
* Trace fossils
Preservation of Unaltered Parts
The shells of invertebrates and single-celled organisms or vertebrate bones and teeth may be preserved unaltered if they are made of stable minerals such as calcite and phosphate.
Examples:
* Preserved echinoderms and foraminifera made of calcite
* Bones and teeth of vertebrates, conodonts, and outer covering of trilobites made of phosphate
Preservation of Unaltered Parts
Some aragonite shells may be preserved unaltered, but aragonite often recrystallizes to calcite
Examples:
* Clam shells
* Snail shells
* Corals
Preservation of Unaltered Parts
In very rare cases, soft parts may also be preserved unaltered
(methods)
- Mummification
- Amber encasement
- Freezing
Types of
Chemical Alteration of Hard Parts
- Permineralization
- Replacement
- Carbonization
Permineralization
(AKA petrification) the process in which minerals are deposited by water in the pore spaces of plant material, bone, and shells resulting in the fossil becoming much heavier than the original hard parts
* Example: Petrified wood
Replacement
the molecule-by-molecule substitution of a mineral of different composition for the original material
* Common mineral substitutions include silica and pyrite
Carbonization
preserves plants or animals through the decomposition of organic matter that slowly loses its liquids and gases leaving a thin carbonaceous film, usually in fine-grained sediments (shales)
* Commonly plant material undergoes this process, but many fish and invertebrates can also be preserved this way
Trace Fossils (Ichnofossils)
Types of Trace Fossils
- Mold
- Cast
- Tracks, Trails, Burrows, and Borings
- Coprolites
Mold
organisms buried in sediment may decay or dissolve away leaving a cavity or mold
Types of:
Molds
- Internal Mold
- External Mold
Internal Mold
an impression of the inside surface of skeletal hard parts
External Mold
an impression of the outside surface of the skeleton or bone
Cast
a true replica of the original skeleton or shell formed by the filling-in of a mold by sediment
* Can be difficult to tell the difference between a cast and altered hard parts
Tracks, Trails, Burrows, and Borings
left behind by organisms and usually preserved when they are quickly buried after they are created
Coprolites
fossilized fecal matter
