Introductionto
Fossils Dr. S.P.Qureshi
Department of Botany,
J.M.Patel College,Bhandara.
Fossils➢ Remains of plants or animals in Geological past.
➢ Study of such plant or Animals which were living in past but extinct now.
➢ It is imprint of nature in womb of earth.
Fossilis means “to dig up”. In earlier study large no of things dug out
of earth crust were called fossils e.g. Minerals
Study of fossils require
1. Knowledge where fossilization take place
2. Type of rock in which fossils founds
3. Knowledge of geological time scale so that age of fossils calculated.
Plants fossils rarely preserved than animal fossils because their tissue
normally do not contain calcified structure. Hence they completely decomposed
before fossilization.
Megafossils – e.g. leaves, fruits, seeds
Microfossils – spore, pollen grain
Fossils Formation
It is very rare that entire plants or animals preserved intact.
Generally its parts get separated from mother plants. Suitable condition
for fossilization is acidic water, low O2 (which stop decay of plants).
Presence of sedimentary materials. E.g. Carbonate, Silicates. In process
of fossilization the part of plants and animals buried within well protective
matrix in earth crust, which is brought by river.
The sand and mud along with organic matter brought by river get
deposited in the form of layer which protect these fossils. Similar layer get
deposited continuously at bottom of sea and like. During course of time,
the lower layer under weight of upper one and upper one under pressure
of water above become compressed and generally harden into stony rocks.
These rocks made up of number of layer called sedimentary rock. These
rock contain animals or plant of fossils.
Sedimentary rocks.Accumulation of rock particle results information of sedimentary
rocks. Weathering and mechanical abrasion of existing rock or chemical
weathering, flooding of existing rock. These rock particle of sediments
accumulate and water squeezed out of them. During course of time this
make more compact and rocky structure.
TYPES OF FOSSILS
1 .Sedimentary Rocks (e.g. Coal) : Majority of plant materials are
preserved as fossils in sedimentary rocks. Coal is the best known example of
sedimentary rook. Sediments of Plant origin represents dense frosts of the
world of earlier times. Least metamorphosed coal shows maximum details
of fossilized or preserved plant material. Therefore lignite's (early stage of
coal formation) carry less crushed plant parts and their details can be studied
easily . Pant parts get excessively crushed in bituminous coal and anthracite
coal because they show more degree of metamorphosis than lignite coal.
Bituminous coal is of great importance in the study of palynology because
pollen grains are best preserved in this type of coal.
1.Impressions:
This is a type of fossils in which
impression or negative replica of the plant part is
clearly visible on the rock upon splitting. The
surface of the plant part involved is visible in this
type of fossil. The entire shape of the organ is
clearly visible in an impression but cellular
details are not visible. During the course of the
formation of impression type of fossil there is no
involvement of the organic matter.
➢ Diatomite :
Diatoms are unicellular algae
belonging to class Bacillariophyceae. Their
walls have silicon deposits. The sedimentary
rock formed by the remains of diatoms is
called diatomite. In due course of time diatoms
keep on depositing at the base of sea, oceans or
lakes and form sedimentary rock.
Pseudo fossils or Dendrites:
Pseudo fossils or dendrites are completely
inorganic structures of various types. They
often resemble plant organs. Their formation
takes by the deposition of minerals due to
seepage or percolation of water in rock
crevices. They superficially resemble leaves
of ferns.
➢ Mummification:
The process of the formation of fossils in ice-
frozen environments in the polar regions is termed as
mummification. The moisture of the tissue of the
organism gets converted to very small or
microcrystals of ice. It is almost a process similar to
deep freezing.
➢ Molds:As the name indicates molds are formed by
three-dimensional structure, dissolved by seepage of
ground water leaving a hollow cavities resemble with
the original organ in the rock. Such hollow cavities
resemble with the original organ in size and shape.
External features of the plant in three-dimentional
view are best seen and studied in molds, e.g.
ornamentation of seeds and fruits. The process of
mold formation is similar to modern day sculpture
making. A sculptor makes the original “original” with
wax or wood and prepares the “Mold”.
➢Cast:
Decay of tissue in an organism results in the
formation of a hollow. When this hollow gets filled
with mineral i.e. sediments, it results in the formation
of a cast. An exact replica of the original plant
material is thus resulted.
➢ Compression
When bulk of the plant material gets compressed in
layers of sediment, the fossils are called compressions.
By the laying of the additional sediments from above,
water quizzes out of the parts of organisms and this
makes them more compact and flattered. Ultimately a
thin carbonaceous film remains in the compression
fossil and this corresponds to the original outline of
the parts of the organism. Differing from impression
type of fossils (in which no cellular details can be
seen) some cellular details can be seen in compression
type of fossils
➢ Petrifactions:
Petrifactions are formed when parts of the plant
are completely submerged in water reservoirs
containing dissolved minerals. In the process of
their formation, several types of soluble. The
soluble minerals include carbonates, silicates and
iron compounds. The minerals surrounding the
cellular remains precipitate and form the rock
matrix. This precipitation is resulted due to
gradual evaporation of moisture.
How are fossils studied?
Impressions:
These are studied generally by preparing artificial casts which
are also called positives.Molds:
These are studied exactly like that of impressions
Compressions:
These can be studied either by transfer technique or by maceration in
Schulze’s solution or by first softening and then cutting thin sections by
microtomy. Microtomy is done by embedding the material in plastic.
Petrifactions:Etching techniques or peel method was then discovered. In this
method polished surface of the rock is etched by sulphuric acid or nitric acid.
This surface is then flooded with acetone and a film of cellulose acetate is
rolled down. After some time, when the film is dry, it is removed from the
surface of specimen. A clear impression of specimen develops on the film. By
definite methods, it is made permanent and studied under microscope.
How are fossils reconstructed and named?
Fossils of the entire plants only rarely been reported. Generally an organ or
a part of the plant is seen preserved as fossils. A detailed scientific
knowledge is required to reconstruct a plant.
Some factors which help in reconstruction of plant Fossils:1. Structural similarity between the fossils.
2. Regular occurrence of the same type of fossils in the same area.
3. Ovules of different fossils containing similar type of pollen grains.
4. Relationship between different fossils is also assigned on the basis of
pollination
Concept of Form genus or organ Genus:
separate generic names are given by the palaeobotanists to the fossils of
the detached organs or fragments. Each of these organs or fragments is called a
form genus or organ genus. Similar to the present day living plants, binomial
system of nomenclature is also applied to name these form genera.
1. Leaf – Nipaniophyllum raoi
2. Fructification – Sahnia Nipaniensis
3. Stem – Pentosylon Sahnii
importance
1. Evidence of prehistoric life
2. Provide missing link in evolutionary chain
3. Help in construction of physiological classification
Determination of age of fossils
The radioactive isotopes decay and lead to stable isotopes. In this
process, the energy is released. The rate of decaying of any radioactive
isotopes and its giving rise to stable isotope is always constant. The age of
rock and plant can thus be calculated by measuring relative quantities of
radioactive isotope and the stable isotope.
Top Related