Death and Fossilization

Students will be able to describe how fossils form and interpret the taphonomy of skeletons and bonebeds.

Importance of understanding the circumstances surrounding fossilization.
Taphonomy: Study of all natural processes affecting an organism after death.
- Processes: Decay, scavenging, fossilization, erosion.
- Movement of carcasses: Dinosaur carcasses can be moved considerable distances post-mortem.
- Bloat-and-Float:
  - Post-death, decay generates gases causing carcasses to swell and float, aiding transportation by water.
Rare completion of dinosaur skeleton finds:
- Typically, few isolated bones are discovered.
- Factors contributing to disarticulation:
- Carnivore consumption
- Water currents causing differential transport based on bone weight and shape
- Sun exposure weakening bones
- Partial burial leading to erosion of exposed bones
- Trampling by other animals
- Mineral leaching due to plant roots

Disarticulation can occur due to multiple forces acting on fossilized remains.
- Gas expansion and subsequent floating due to decay.
- Erosion and water impact during heavy flooding.

Example: Skeleton of Argali sheep (Ovis ammon) in Gobi Desert.
- Observations: Complete disarticulation and flesh stripped off.

Even buried fossils may undergo modifications:
- Weight from overlying layers can lead to flattening of remains.
- Plastic Deformation: Pressure alters the fossil structure permanently.

Critical for preservation: Bone burial.
- Can occur through natural means such as sinkholes, predator actions, or most commonly through sediment coverage from water (i.e., floods).
Better fossilization in:
- Wet environments compared to arid conditions.
- Low elevations are more conducive to sediment build-up than high elevations where erosion prevails.
Fossil finds:
- Common in ancient river (fluvial) and lake (lacustrine) deposits where fine-grained sediments can preserve more delicate structures such as feathers.
- Occasional finds in ancient coastal environments if conditions were right (e.g., washed out to sea).
- Rare fossils in desert environments due to lack of sedimentary deposition.
- Exception: Ancient Cretaceous Mongolia - rivers created deltaic plains that buried large animals.
Observation: Preservation of dinosaurs in unusual crouching positions due to sudden sand dune collapse.

Types of Rocks:
- Fossils predominantly found in sedimentary rocks.
- Basic rock types:
1. Igneous Rocks: Formed from cooled magma or lava.
2. Metamorphic Rocks: Formed under heat and pressure from existing rocks.
Sedimentology: Science of sedimentary rock formation.
- Differentiation based on accumulation types:
- Mud and silt form mudstone and shale (indicate lake environments).
- Sand forms sandstone (indicates beach, river, ocean floor).
- Coal indicates swampy conditions.
- Limestone usually indicates ancient shallow marine environments.

Conditions affecting discoverability:
- Many fossils are destroyed by geological processes or remain too deep to excavate.
- Fossils need exposure for paleontologists to find them, which often occurs in environments of high erosion (e.g., badlands).
Methods for fossil hunting:
- Use geologic maps to identify potential fossil sites.
- Fossils ideally should be minimally exposed.
Overburden Removal:
- Involves removing rock and dirt covering fossils, using various tools.
- Final excavation requires precision and delicate work.
Mapping:
- Important step for understanding spatial relationships between bones for reconstructive efforts.

Initial Steps:
- Removal of overburden to expose fossils.
- Application of protective materials (e.g., paper towels) and plaster jackets to secure fossils during transport.

Clues to the history of a dinosaur's remains:
- Disarticulation due to carnivore feeding or water movements.
- Orientation of bones provides insights into transportation dynamics.
- Cloth-like marks on bones could indicate interaction with carnivores.

Key areas of understanding include:
- Conditions facilitating fossilization.
- Fossil locations and environments histories.
- Recognition of taphonomic processes affecting discovered skeletons.

Illustrated sequence:
1. Initial unearthing of fossil top and sides.
2. Application of soft materials (e.g., moist paper towel) for cushioning.
3. Final covering with burlap and plaster for protection during transport.

Geology Kitchen – The 3 Types of Rocks [Video]
National Geographic articles and videos related to dinosaur excavation and research.
Recent fieldwork examples from the University of Alberta and various museums.

Understanding taphonomy, fossilization conditions, and the various preservation methods provides a key framework for studying paleontology.