Modes of preservation (lecture) Flashcards
What is an example of fossils providing hidden links in evolution?
Archaeopteryx- (Bird with teeth or Lizard with feathers)
What puzzle was linked to the burgess shales?
That of Anomalocaris thought to be a worm/centipede until linked to Peytoia (thought jellyfish) which was the mouth and tentacle was raptoral appendages of apex predator
What is an example of how fossils can be important for paleoenvironmental and paleoecological studies?
Footprint marks of a bird found in miocene rock in the Pyrenees which shifted the idea of deep marine to shallow lacustrine
How can fossils be used to distinguish divergence time?
If A taxon group found in record followed by B we can suggest A is common ancestor but if C isn’t found to later we have to estimate using ‘ghost range’ to suggest link
How can fossils be used to age geological strata?
Can see the different fossils with their known ranges and see where they overlap to give age
What is the use of fossil assemblage to age geological strata called?
Biostratigraphic ageing
What are the benefits of biostratigraphic ageing?
Cheap, quick, accurate
What is needed for biostartigraphic ageing?
1) preservation allows identification
2) ranges are adequately known
3) fossils have not been redeposited or reworked
What are the 2 groups of fossils?
Body
Trace
What are body fossils?
partial or complete remains of plants or animals
What are trace fossils?
remains of the activityof ancient organisms such as burrows or tracks
What are body fossils usually like?
The hard parts (shells, bones, woody tissue)
What are the 3 common compounds of body fossils?
CaCO3 - calcium carbonate
SiO2 - Silica
CaPO4 - Apatite
What is calcium carbonate usually used to preserve?
corals, bryozoans, brachiopods, molluscs
many arthropods and echinoderms
What are echinoderms?
Sea urchins
What is usually preserved in silica?
Most sponges and spines of echinoderms
What is usually preserved in Apatite?
Some brachiopods and some worms
What are some examples of organic hard tissue that can be preserved in fossils?
Chitin
Collagen
Keratin
How can organic hard tissues exist?
In isolation or association with mineralised tissues
What is the name of the fossilisation process?
Taphonomic
What is needed for a trace of an organism to be seen in fossil?
the decay process needs to be arrested or inhibited
What factors are important for decay?
Supply of oxygen
Temperature
pH
What will happen to organic material in aerobic conditons?
microbes breakdown organic carbon by converting C and O to CO and water
What will high temp and neutral pH do to decay rate?
Increase the rate of decay
What can cause a slow of decay?
Unusual pH (acidity of peat bogs)
Anaerobic conditions
What physical processes can affect fossil preservation?
Breakage & Diagenesis
fragmentation
in situ decay/transport/scavenging
abrasion (rolling)
disarticulation
Why might bioerosion of fossils occur?
Bioerosion (borings) might occur in fossils rich in calcium carbonate which might be harvested by other organisms
What does corrosion and dissolution of fossils lead to?
moulds and casts (imprint of internal and external rock structure)
What can cause the flattening of fossils?
The weight of the overlying of sediment on top
How can recrystallisation affect fossils?
Calcite and aragonite both CaCO3 with different minerology Calcite is more stable so the change from calcite to aragonite can destroy the internal structure
What has recrystallisation from calcite to aragonite done to the fossil record?
Created a bias of calcite mineralised fossils
What process occurs at high organic content low rate of burial for fossils?
Phosphatization
What process occurs at high organic content high rate of burial for fossils?
preservation in carbonate
What process occurs at low organic content high rate of burial for fossils?
Pyritization
What is exceptional preservation?
When soft tissue of an organism is preserved in the fossil record?
What is an example of phosphatization of exceptional preservation?
Preservation of arthropods (to gill filaments) in Orsten Sweden upper Cambrian
What is an example of exceptional preservation by pyritization?
In Hunsruck slate, early Devonian Germany
What is an example of exceptional preservation in carbonate?
Tully monster - Mason Creek , Carboniferous Illinois
What is an example of carbonate and phosphate exceptional preservation?
Eel and shrimps in Granton Shrimp Bed, Carboniferous, Scotland
What is important with exceptional preservation?
Some decay must occur before being removed from normal decay conditions as bacterial film act as preserving medium
What conditions will carcasses need to be transported to for exceptional preservation?
Anaerobic
What does anaerobic conditions to for fossil preservation?
1) Lack of oxygen means no animals on sea floor- carcasses not scavenged or damaged
2) Anaerobic environment slows decay
3) Anaerobic environment enhances growth of early diagenetic minerals
What is an extreme example of an organism being placed in anaerobic conditions?
Fly in amber from tree sap (but amber only been around for 150 million years)
What is the name of sites of exceptional preservation?
konservat lagerstatten
What would the burgess shale paleoenvironment been like if konservat lagerstatten didn’t occur?
would be significantly less organisms to re-piece fauna
What are the types of konservat lagerstatte?
Stagnation
Obrution
Traps
What is obrution lagerstatte?
rapid burial
What is traps lagerstatte?
instant preservation in restricted situation
What is stagnation lagerstatte?
anoxic or hypersaline conditions
