Fossilization
Aiman Batool
Roll No. M06
BS(H) ZOOL-VIII
FOSSILIZATION
• It involves all the process that occur between the covering of
an animal in some comparable medium and formation of
fossils.
FOSSILS:
• Preserved remains or traces of animals, plants, and other
organisms that were present in the past and then become
the part of earth crust
Factors That Can Affect Fossilization
• There are two factors which affect fossilization
1. Animal Nature
2. Environment
1) NATURE OF ANIMAL
• Hard parts have better chances of fossilization i.e., wood, bones,
hard sells, teeth etc.
• Soft parts i.e., fossils of jelly fish decompose quickly because they
have more water content.
• Under remarkable condition, soft bodied animals may be preserved
as impression.
• Two factors are promote fossilization:
Escape from immediate destruction
Rapid burial
FOSSILS OF JELLY FISH FOSSILS
OF SHELLS
2) ENVIRONMENT
“Environment is the surrounding in which
an animal live.”
I- Marine ii- Land
iii- Bogs and sand deposits iv- Natural petroleum
seeps
v- Amber vi- Caves
vii- Volcanic ash and dust viii- Ice and frozen
soil ix- Deserts
I- Marine
• There are a number of animals which take
calcium carbonate from water and build
shell.
• These bony fishes when dead, their shells
and skeleton accumulate at the bottom where
they are buried by soft sediments.
• In sea soft sediments are formed by
precipitations of chemicals.
• Marine animals are most likely to fossilize as MARINE FOSSILS
decay is checked by salt water.
ii- land
• Deposition of land is not continuous
process as it is restricted to small areas.
• Fossils of terrestrial animals are mostly
found un lakes, swamps and deserts; may
also preserves by dessication.
• Floods play very important role as animals
are moved along the channels of water and
buries in sand, mud and finally preserved.
iii- Bogs and Sand Deposits
• Semifluid substances of sand make natural death trap.
• These are then quickly preserved and fossilized.
iv- Natural Petroleum Seeps
• Large animals are usually
trapped by natural petroleum
seeps.
• There are number of localities
where animals are nicely
preserved.
• Even soft parts are
preserved.
v- Amber
• Spiders and insects are preserved in amber.
• Amber is resins that are secreted by certain trees
even microstructure is preserved
• Fossils of insects, spiders etc.
vi- Caves
• Other sources of fine fossils are caves
which are mostly used by carnivores.
• Their prey is taken to caves and hard
parts are left there which are then
preserved due to environmental
conditions.
vii- Volcanic Ash and Dust
• Volcanic ash and dust are in rare cases even lava may act as preserving
material.
viii- Ice and Frozen Soil
• The best material for preservation is ice and frozen soil.
• Many complete carcasses are found in frozen soil.
ix- Deserts
• It is not a good preserving material for preservation.
• But in rare cases i.e., nests of Dinosaurs were found preserved in deserts
of Magnolia.
TYPES OF FOSSILS
There are two types of fossils.
1- Unaltered fossils
2- Altered fossils
Unaltered fossils
Unaltered fossils are formed when organic parts remain unchanged for
a considerable period after burial and ultimately appear without any
change.
These are in chemical equilibrium with preserving material which may
be ice, oil or sediment.
There are two types of unaltered fossils.
(i) Complete Unaltered fossils
(ii) Incomplete Unaltered fossils
(i) Complete Unaltered fossils:
Complete carcasses which are found
unaltered for after a long time of burial.
These are found buried in favorable
material i.e., ice and oil.
Even soft parts as fleshy meat is
preserved along with teeth and bones.
Organism is basically preserved in a
medium that protect them from bacterial
decay.
EXAMPLES OF MEDIUMS
FOR PRESERVATION
1- ICE
2- OIL
3- AMBER
4- DESERTS
1- ICE
The best known example of fossil preserved in ice wooly Mammoth of
Siberia and Alaska.
Mammoth was present in Pleistocene period.
Firstly, wooly Mammoth was discovered in frozen soil of Siberia.
This fossil was 30,000 years old.
Wooly Mammoth was so nicely preserved that even the fresh food was
found preserved in buccal cavity.
50 complete carcasses have been found preserved in frozen soil and ice.
FROZEN FOSSILS IN ICE
2- OIL
Remains of wooly Rhinoceros have been found in oil saturated in Poland.
Bison fossil also found in Siberia.
3- Amber
Insects and other small animals are
usually found preserved in amber
(resins produced by trees).
It is also very good preserving
material even the microstructure is
very nicely preserved in amber.
4- Deserts
Another medium of preservation of complete bodies in desert.
Many desert animals have been dried out by wind and buried in shifting
sand, resulting in well preserved skin and soft parts.
(ii)- Incomplete Unaltered Fossils
These are fragmentary fossil remain like pieces of wood, bones of
vertebrates, shells of invertebrates commonly found well preserved
with little or no change since cretaceous (in clay).
Altered Fossils
Many changes occur from the death of the organism until it is completely
fossilized.
Footprints, tracks and trails are fossilized remains or evidences of everyday life
of animals.
They indicate the function of animal.
These are of several types.
1- Petrified Altered
2- Mould fossils
3- Cast fossils
4- Trace fossils
1- Petrified altered fossils
Bones and other hard parts become denser due to the deposition of
sediments or minerals from the percolating water..
Petrified fossils are thus formed (the pores and spaces are filled by
minerals).
The added solid material may have the same chemical composition as the
organic material or it may be different.
A- Permineralization
B- Mineralization
C- Carbonization
A- Permineralization
These fossils are formed when the skeleton of organic remain is porous (empty
spaces).
The spaces may be filled by materials from surrounding and this is called
permineralization.
Vertebrates bones are usually preserved by permineralization.
B- Mineralization or Replacement
Sometimes the skeleton may get dissolved or replaced by minerals present in
the environment, this is called permineralization.
This is a gradual process.
The microstructure is usually finally preserved.
It occurs in plant tissues or wood and is rare in animal skeleton.
Most replacement materials are:
calcite
silica
pyrite
hematite
Aragonite
C- Carbonization or Distillation
Volatile substances of organisms or
organic materials may sometimes be
distilled away leaving behind a
carbon to indicate the outline of a
skeleton.
This is called distillation or
carbonization.
Leaves are generally preserved by
distillation.
Ichthyosaur (early fish like reptile)
found preserved by distillation.
2- Mould Fossils
At the time of deposition around organic material, the skeleton may get
dissolved leaving behind a cavity this is called as mould.
It indicates the external morphology of the organism.
3- Cast Fossils
If the fossil is filled by minerals in
nature like quartz, we may get a natural
cast also called pseudomorph.
If the cavity remains with original
skeleton it is called true morph.
Internal casts are formed when the
shell is filled with sediments and shell is
lateral dissolved leaving behind an
internal cast.
It indicates the internal impression.
4- Trace Fossils
These are of five types.
a) Imprints
b) Coprolites
c) Tracks
d) Trails
e) Gastroliths
a) Imprints
Moulds of thin organism like leaves are commonly called as imprints.
b) Coprolites
Trace fossils that are dropping of animals (fossilized fecal matter) ranging in
size from very small to very large.
They undigested hard material of animals and plants that were eaten.
Coprolites indicate food and food habits of the animals.
The animal may be carnivorous, omnivorous or carnivorous.
Chemical analysis of coprolites indicate the remains of eaten animals.
c) Tracks
Animals leave impressions of certain body
parts on mud or sand during travel e.g., footprints.
We can tell whether animal was bipedal, or
whether move by jumping, crawling, agile,
ponderous or move by running.
They are generally preserved in semi-arid or arid
areas.
Footprints occurring in series may indicate the
size of the foot or length of limbs.
Many footprints of Dinosaurs are found in red
stones USA.
d) Trails
These are the impressions of body during crawling on earth e.g.,
Earthworm.
e) Gastroliths
These are small rounded smooth stones present in rib cages of
dinosaurs.
These were used for crushing of food.
They are also considered as trace fossils.
