How do fossils form Biological materials Conditions needed

How do fossils form? Biological materials Conditions needed for preservation Types of preservation, types of fossils Fossilization

Biological Materials Vertebra Crustace Mollusk te an DNA DNA Protein Plant DNA Protein Collagen Cellulose Mineral bone Teeth Fossilization Mineral shell Lignin 2

Conditions required for fossilization 1. Retard decay and chemical and physical breakdown 2. Burial 3. Fixation Fossilization 3

Step 1: Retard decay and chemical breakdown • Anaerobic environment Reduces decay, but acidity may destroy DNA, proteins, and carbonate-bearing minerals O- • Clay films Mg+ Ca++ Fe++ Fossilization C Carbonyl … first product of bacterial breakdown 4

Step 2: Burial • Removes object from destructive environment • Paves entry to rock record Fossilization 5

Step 3: Fixation • Reduces vulnerability to breakdown • Drying or freezing • Clay minerals fix organic material • Minerals entering cells • Mineral alteration - e. g. aragonite to calcite or dolomite Fossilization 6

Kinds of Fossils • Unaltered remains • Altered Hard Parts – Compression – Permineralization – Recrystallization – Replacement • Traces – Impression – Mold-Cast – Tracks, trails, and burrows – Coprolites - that’s fossil poop, by the way • Molecular fossils Fossilization 7

Unaltered Remains • Original tissues preserved intact Fossilization – Drying, freezing, or preservation in 8 amber

Compressions • 2 D remains of 3 D material • Retain organic material Fossilization 9

Permineralization • Mineral infilling of porous spaces in skeletal elements like wood, bone, and echinoderm plates • Can preserve cellular detail Fossilization 10

Recrystallization Loss or blurring of original shell structure as shell is converted to interlocking crystals. Fossilization 11

Replacement • Original material dissolved away and replaced by another mineral Fossilization Pyritization, Silicification, Calicification, others 12

Impressions 2 -dimensional imprints without any organic material Fossilization 13

Mold / Cast Fossilization • Physical characteristics of organisms are impressed onto rocks, especially coarse porous rocks like sandstones. 14

Ichnofossils • • Tracks Trails Burrows Other evidence that organisms were present • Only evidence for behavior Fossilization 15

Coprolites • Fossil Excrement • Extremely informative - what were they eating? Fossilization 16

Molecular fossils • • Chlorophyll Flavinoids Collagen DNA Lipids Proteins And their biochemical breakdown projects Fossilization 17