Types of Fossils

Overview

• Fossils are divided into body fossils and trace fossils (ichnofossils).
• Body fossils include parts like bones, claws, teeth, and soft tissues.
• Trace fossils include footprints, nests, dung, and toothmarks that record dinosaur behaviors.

Types of Fossils

1. Mold Fossils
   • A fossilized impression, a negative image of the organism.
2. Cast Fossils
   • Formed when a mold is filled in.
3. Trace Fossils (Ichnofossils)
   • Include fossilized nests, footprints, and gastroliths.
4. True Form Fossils
   • Fossils of the actual animal or parts of it.

Formation of Fossils

• Unaltered Preservation: Organisms trapped in amber.
• Permineralization/Petrification: Minerals replace organic tissues, forming a rock-like fossil.
• Replacement: Hard parts dissolve and are replaced by other minerals.
• Carbonization/Coalification: Only carbon remains; other elements are removed.
• Recrystallization: Hard parts revert to stable minerals or grow larger crystals.
• Authigenic Preservation: Molds and casts of organisms that have been destroyed or dissolved.

Body Fossils

• Bones: Main source of dinosaur information.
  • First dinosaur bone discovered in 1818.
  • First nearly-complete skeleton found in 1858.
• Teeth and Claws: Indicate predation and diet.
• Eggs, Embryos, and Nests: Provide insights on reproduction and nurturing behavior.
  • First fossilized eggs found in 1869.
• Skin: Indicate texture and appearance.
  • Example: A T. rex skin imprint suggests pebbled skin.
• Soft Tissues (Muscles, Tendons, Organs): Extremely rare due to decay.
  • Example: Theropod fossil Scipionyx with soft tissue impressions.

Trace Fossils

• Trackways: Set of footprints indicating movement patterns.
  • Provide information on speed, stride, walking behavior, and herd movements.
• Toothmarks: Found on bones, indicate feeding behaviors.
• Gizzard Rocks (Gastroliths): Smooth stones swallowed to aid digestion.
• Coprolites (Fossilized Feces): Offer dietary and habitat information.
  • Examples: Large coprolites indicate large dinosaur species like sauropods.
• Burrows and Nests: Show behavioral aspects related to living environments.

Interesting Insights

• Lack of tail-furrow fossils suggests dinosaurs held tails erect.
• More theropod footprints are found than herbivores despite the latter being more numerous, possibly due to habitat preferences for fossilization.