The Fossil Record

Question 1

What makes a useful fossil?

Answer 1

When an organism dies and avoids destruction by biological and physical processes. It is transported into an environment where it is covered in sediment and fossilised.

Question 2

What must sediment avoid during fossilisation?

Answer 2

Sediment must avoid diagenetic or metamorphic processes which later the rock.
Also avoid later destruction by erosion.

Question 3

What is the difference between immediate burial of organism and decay and transport?

Answer 3

Immediate burial - perfect preservation (rare)
decay and transport - only hard parts left

Question 4

What can cause incompleteness of the fossil record?

Answer 4

• Sediment only accumulates over a small area of the earth
• Only a small fraction of organisms are fossilised
• Most will be destroyed by rock (metamorphic processes)
• Only a fraction of fossils formed will be collected and studied

Question 5

What are the biases of the fossil record?

Answer 5

• Certain organisms / parts are preferentially preserved
• Some environments preferentially preserve sediment and therefore fossils
• Old rocks more likely to be destroyed
• Collector bias

Question 6

What organisms leave fossils?

Answer 6

BACTERIA: certain bacterial sheaths, stromatolites
PROTISTS: those that form exoskeletons and resting cysts
PLANTS: woody tissues (lignin), cuticle, spores
FUNGI: chitinous spores and hyphae
ANIMALS: those with strong exo and endo skeletons

Question 7

What are stromatolites?

Answer 7

Layered sedimentary formations created by cyanobacteria.

Question 8

What are the environmental trends that may bias the fossil record over time?

Answer 8

• Sea level changes: affects area of shelf and intercontinental seas
• Continental configuration: affects sediment production, sea level, amount of tectonic activity
• Atmospheric composition: O2 levels, effects weathering rates, sediment production, fossil survival

Question 9

How do you interpret the fossil record?

Answer 9

By plotting the spatial (palaeogeographical) and temporal distribution of fossils.

Question 10

What should you consider when interpreting the fossil record?

Answer 10

Ghost ranges (sister taxa originating at different times)
Probabilities of range extensions
Volume and exposed area of rock.

Question 11

Are dinosaur fossil records good?

Answer 11

Dinosaur fossil records are good but biased towards animals that lived by water (higher sedimentation rates)