How do fossils form?
Biological materials
Conditions needed for preservation
Types of preservation, types of fossils
Biological Materials
Vertebrate
Crustacean
Mollusk
Plant
DNA
Protein
DNA
Protein
DNA
Protein
DNA
Protein
Collagen
Collagen
Collagen
Cellulose
Mineral shell
Lignin
Mineral bone
Teeth
Fossilization
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
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Fossilization
• 2D remains of 3D
material
• Retain organic material
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
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
2-dimensional
imprints
without any
organic
material
13
Fossilization
Mold / Cast
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
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