Fossilization

Environmental Scene for Fossil Preservation

• Various landscapes influencing fossil preservation potential:

  • Mountains: high elevation, minimal sediment deposition.

  • River and Floodplain: ideal for quickly burying carcasses with sediment during floods.

  • Forest: potential for decomposition from plant roots and microbes before fossilization.

  • Lake: offers conditions for sediment deposition that can bury carcasses.

  • Desert: dry environment, slower sediment deposition primarily from wind.

Effects of Rain on Carcass Burial

• Flooding from Rain:

  • Rain causes rivers to overflow, depositing sediment over carcasses near rivers and lakes.

  • Burial occurs primarily in:

    • Carcasses near the river.

    • Carcasses on lakeshores.

  • Areas where burial is unlikely:

    • Desert: slow sedimentation.

    • Forest: decomposition is likely.

    • Mountainside: lack of sediment cover leads to degradation.

Marine Environments and Dinosaur Fossils

• Sedimentary Environments in Oceans:

  • Most fossils in marine sediments are from marine animals.

  • Rare occurrences of dinosaurs washed offshore:

    • Sometimes preserved in ancient marine sediments.

• Examples of dinosaur fossils found in marine rocks are known (though rare).

Types of Sedimentary Rock and Their Formation

• Sandstone: formed from sand, typically deposited in rivers, beaches, or dunes.

• Mudstone/Shale: formed from mud or silt, found in lake deposits.

• Coal: formed from the fossilized remains of plants in swampy areas.

• Limestone: formed from chalky sediments, mainly composed of plankton exoskeletons, characteristic of marine environments.

• Incomplete Fossil Remains:

  • Commonly found bones are disarticulated due to various reasons: flowing water, scavenging, or trampling.

Reasons for Finding Incomplete Skeletons

• Reasons why complete skeletons are seldom found:

  • Carcasses in flowing rivers can scatter bones.

  • Possible scavenging by predators.

  • Bones trampled by other animals or displaced by environmental factors.

Fossilization Processes

• Permineralization:

  • Internal spaces of bones and tissues filled with minerals carried by water.

• Replacement:

  • Original materials replaced by minerals, leading to fossil casts/impressions.

• Example:

  • Stigmaria: fossilized tree root illustrating replacement process.

Taphonomic Effects on Fossils

• Plastic Deformation:

  • Asymmetrical skull of a tyrannosaur due to pressure from surrounding sediment.

  • Weight of sediments leads to squishing without breaking the bones.

Summary of Events from Death to Excavation

• Correct Order of Events:

  1. Death of the dinosaur.

  2. Burial occurs shortly afterward.

  3. Fossilization begins with mineral infill or replacement.

  4. Erosion exposes fossils at the surface over time.

  5. Excavation by paleontologists to recover fossils.

• Correct Sequence: Death, Burial, Fossilization, Erosion, Excavation (Option B)