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.