Paleobotany is a study of preserve of vestiges (remaining) of geological past.
More comprehensively, it is a part of paleontology or paleo-biology which deals with recovery and identification of plant remains.
Paleobotany can be defined or approached from the botanical point of view where emphasis is given on plant remains and from the geological angle where rock containing fossil is the primary concern.
- In reconstructing the first ecological system and climate known as paleo-climatology.
- In understanding the fundamental green plant development and revolution.
Regarding taxon of the plant-fossil, a taxonomist can ask 4 basic questions:
1. What is it?
2. When did it arise?
3. How did it originate?
4. How did it acquire its present status or distribution?
Last 3 questions can be answered by paleobotany.
Fossils may be defined in various ways:
- Fossil is any evidence of the prehistoric life. Therefore, fossil is the record of former life.
- The word ‘fossil’ is derived from the latin word ‘fodere’ which means ‘to dig’. Therefore, fossil is something occurring in earth and required to be dug out.
We can also say, fossil is the marker of the geological past.
- Fossil is the remain of whole organism or some part of the organism or the direct evidence of the former existence of an organism preserved in consolidated sediments of the earth.
But a plant fossil is any preserved part of a plant that has long since died. Such fossils may be prehistoric impressions that are because of many millions of years effort.
Good to know:
- The first majority of the fossils are found in sedimentary rocks.
On the basis of size :
1. Micro fossil
2. Macro fossil
- Type of fossil that cannot be observed by naked eye: Microfossil: Pollens, spores.
- Type of fossil that can be observed by naked eye: Megafossil: Leaves, flowers.
On the basis of the nature of fossilization :
4. Casts and molds
5. Compaction or mummification
- Three dimensional structural details are usually well preserved in a matrix of silica, calcite, dolomite and other substances.
- These types of fossils are formed by involving molecule by molecule replacement of the plant part by soluble minerals that eventually hardens.
- These are the only means of transformation of organic tissues into stones. In this case, the buried plant materials absorb mineral solutions like sulfate, silicate, phosphate etc. This infiltration is followed by precipitation so that CaCO3, MgCO3, FeS, silica etc. can enter within the plant tissue.
- Although most of the organic materials may be destroyed but at least some original cell wall compounds often remain making the whole structure stone like.
- This is the most common type of fossil in those cases where most of the organic matter of the plant is preserved with the impression of the plant. The fossils are known as compression.
- This type of fossils are formed as a result of vertical pressure of the sediments. The buried plants or plant parts are highly compressed due to weight of the sediment lying over them.
- These are the prints made by the plants or plant parts coming in contact with soft clay. In this case, essentially no organic matter is present. The external features are evident as an imprint in the rock.
4. Casts and molds
- These are one of the most common types of fossil.
- A cast results from filling of a cavity formed by the decay of some or all of the tissue of a plant part. The removal of the plant tissues leaves a cavity or mold which becomes subsequently filled with mud or sand and which upon hardening becomes a cast.
- These are the plants or plant parts compressed by vertical pressure.
- Masses of plant fragments without intervening matrix such as occurring in peat, lignite and coal are large scale compaction.
- Occasionally, especially in leathery leaves or tuft roots, the tissues are retained in mummified condition.
- Ambers are the resinous excretion of certain fossil coniferous trees which flowed due to injuries caused by boring insects. These often dropped to the floor of the forest, gradually hardened and accumulated over long period of time.
- Sometimes certain minerals during their formation or crystallization resemble some plants particularly algae and animals which are considered as fossils.
- Pseudo fossils are visual patterns on rocks that are produced by naturally occurring geological pressure rather than biological process. They can be mistaken easily with true fossils.
Any living species which is apparently identical or closely resembles a species previously known only from fossil i.e. it is as if the ancient fossil had come to life.
E.g. Ginkgo biloba, Cycas sp.
Factors of fossilization
1. It is essential that plant or plant parts must be in a region where deposition is taking place.
2. Some kind of water need to be present e.g. brackish water, fresh water.
3. Plants having hard tissues are more viable for fossilization than those with soft plant tissues.
4. Rapidity of burial and prevention of microbial or autolytic decomposition.
5. Burial in stagnant water.
6. Low amount of available oxygen.
7. Rapid infiltration of minerals.
8. Protection against high winds.
Examples of fossil
Pallavicinites devonicus (Oldest bryophyte fossil)
Protopteridium minutum (Oldest)