Nature of the Fossil Record Flashcards
What does an organism have to do to become a useful fossil?
1) Die and avoid destruction by biological (microbes, scavengers, trampling) or physical (weathering, erosion) processes
2) Be transported into an envrionment where it is deposited, buried and thus incorperated into sediment
3) The organism can then be fossilised by a variety of processes (known as taphonomy)
4) The sediment must avoid diagenetic or meteamorphic processes that alter the rock and destroy the fossil
5) That sediment must avoid later destruction by erosion
6) The fossil must become exposed at the surface and discovered by someone that will study it
Why is the fossil record incomplete?
Sediment only accumulates over a very small area of the Earth at any given time
Only a tiny fraction of the organisms that ever live will be fossilised
Most will subsequently be destroyed with the rock that contains them
Only a tiny fraction of fossils ever formed will be collected and studied
Why is the fossil record bias?
Certain organisms and parts of organisms are preferentially preserved
Certain environments preferentially preserve sediment and hence fossils - aquatic environments are much better at preservation
Older rocks are more likely to be destroyed
Collector bias - poorer countries have less palaeontologists and some palaeontologists show bias to certain fossils e.g. dinosaurs
What organisms can leave a fossil record? How?
Bacteria - certain bacterial sheaths and structures (stomatolites) but these are very rare
Protists - Those that form exo or endoskeletons (radiolaria, diatoms, forams, coccoliths) and resting cysts (dinoflagellates)
Plants - Woody tissues (made from lignin), cuticles (made from cutan) and spores (made from sporopollenin)
Fungi - Chitinous spores and hyphae
Animals - Those with recalcitrant exo and endoskeletons
Where does sediment accumulate?
Sediment is slowly eroded into the sea
Sone faults along the Earth the can cause basins and sediment (and therefore fossils) can be preserved in the basins
Easier to preserve in the lowlands (liek floodplains) than the uplands (like mountains)
Sediment builds up along the continental shelf and so most fossils are found there
Very little sediment falls into the deep oceans - find red clay there instead
What are some long term environmental trends that may bias the fossil record?
Sea level changes (related to long term climate trends and/or continental configuration) - when the sea levels rise the continental shelf increases in size and so more sediment can accumulate and this causes better preserved fossils
Continental configuration - is there more or less continents
Atmospheric composition (oxygen levels) - increased oxygen causes a decrease in the probability of dead matter being preserved as oxygen reacts with what is being fossilised
How is the fossil record successfully interpreted?
Plot the spatial (palaeogeographical) and temporal distribution of fossils
What are some pros and cons of the dinosaur fossil record?
Pros - good fossil record
Cons - dinosaurs were terrestrial which means deposits are rare, not good for fossil preservation and biased towards animals that lived near water
