Overview
This lecture covers the processes of fossilization, factors affecting fossil preservation, and the biases that shape the fossil record, emphasizing geological, environmental, and human influences.
Fossilization Process
- Burial protects carcasses from scavenging, weathering, and disturbance, increasing fossilization chances.
- Geological processes, not just scavengers, are primarily responsible for burial.
- Erosive environments (mountains, deserts, rivers, shorelines) remove and break down sediments and carcasses.
- Depositional environments (lakes, sea floors, floodplains) accumulate sediments and are key fossil sites.
- Fossil occurrence is biased toward environments where burial is frequent and rapid.
Environmental and Sedimentary Influences
- Fine-grained sediments (mud, clay) in low-energy settings protect fossils better than coarse-grained sediments.
- Anoxic (oxygen-poor) conditions, often caused by limited pore space and high organic matter, slow decomposition.
- Excess organic matter creates acids, which can dissolve bones, so mineral-rich sediments are preferable.
- The surrounding sediment's grain size and composition impact fossil preservation quality.
Post-Burial Changes
- Fossils and surrounding sediments undergo compaction, which can distort or flatten fossils.
- Tectonic movements may deform or fragment fossils, complicating anatomical interpretation.
- Permineralization occurs when minerals fill bone pores, enhancing detailed preservation.
Discovery and Research Biases
- Most fossils are found when exposed at the surface via erosion and uplift.
- Geologic maps help target fossil searches by indicating where rocks of the right age are exposed.
- For dinosaur fossils, terrestrial Mesozoic rocks are ideal; marine rocks are generally less useful.
- Preparation in labs and modern imaging (CT scans) are essential for revealing fossil details.
- Funding and research focus are not globally uniform, influencing where and how many fossils are discovered.
Fossil Record Limitations
- Fossil preservation is rare and typically incomplete.
- The fossil record is biased by environment, organism type, and research effort.
- Significant discoveries have geographic and temporal concentrations due to these biases.
Key Terms & Definitions
- Erosion â the removal and breakdown of rocks and sediments.
- Deposition â the process of sediments being laid down, which can lead to fossilization.
- Diagenesis â physical and chemical changes during conversion from sediment to sedimentary rock.
- Permineralization â minerals filling the pores of a fossil, enhancing preservation.
- Anoxic â lacking oxygen, which slows decomposition.
Action Items / Next Steps
- Review depositional vs. erosional environments for fossilization.
- Examine a local geologic map to identify potential fossil-bearing rocks.
- Read about recent dinosaur fossil discoveries in underexplored regions.