1.4 - The Fossilisation of Plants Flashcards
What are plants? Describe their biology and what is good/bad about it.
Modular organisms.
They disarticulate into various organs (leaves, stems, roots, reproductive structures).
This occurs as part of a plant’s normal life cycle and upon death.
One plant can potentially have different fossils (which is good as different pathways of preservation are shown but makes piecing together a plant difficult).
What are the two types of land plants?
Vascular and non-vascular
What are non-vascular plants also known as? Give 3 examples of non-vascular plants.
Also known as bryophytes.
Eg. liverwort, hornworts, mosses
What can vascular plants be subdivided into?
Seedless and Seed plants
Give 3 examples of seedless plants.
Club mosses, ferns, horsetails
What can seed vascular plants be subdivided into?
Gymnosperms and Angiosperms
What is an angiosperm?
All flowering plants - the seeds are enclosed within an ovary (usually a fruit)
What is a gymnosperm?
No flowers or fruits - enclosed/naked seed on surface of scales/leaves - often seeds confined as cones
Why is there bias in the preservation of vascular and non-vasular plants? Give an example
There are various molecules used in both but some are only used/used to a greater extent by vascular plants.
Eg. Structural polysaccharides (cellulose and lignin) build vascular tissues such as xylem and phloem (recalcitrance)
What is the function of xylem?
Conducts water and disolved nutrients upwards
What is the function of phloem?
Conducts photocynthetic products (sugars) downwards
What is the key thing about vascular tissues that gives them more recalcitrance than non-vascular plants?
Their cell walls are made of cellulose which gives rigidity in life and recalcitrance after death
Why are bryophytes (non-vascular plants) less recalcitrant?
They never form xylem tissue
What are phytoliths?
microscopic mineralised bodies (silica) in plant cells - they form as a defence against being browsed upon
What are plant propagules?
spores in non-vascular and some vascular plants - seeds and pollen in vascular plants - decay resistant biomolecules - good preservation potential
How are plant propagules often transported?
By wind so are often on surface of plant - this is why resistant biomolecules which helps preservation potential
What are the 6 modes of preservation for plants?
3D remains, Compression, Charcoalification, Casts of stems and roots, perimineralisation, petrifaction
What are 3Dremains common for?
Pollen and spores
What occurs in compression?
Carbon films (2D - flattened and preserved as carbon) can retain ultrastructure - they create an impression (in counterpart)
What occurs in charcoalification?
burning by fire in the absence of oxygen - 3D structure can be preserved - often cell walls carbonised - cell contents volatised (gone) - delicate structures can be preserved (eg. flowers)
What occurs to create casts of stems and roots?
Occurs in a certain groups more than others where there is a difference between internal and external tissues with internal tissues tending to decay more quickly leaving a hollow interior where sediment can be washed in (eg. fill interior with sediment and cast interior then have coalified layer on the outside that is carbonaceous).
What is perimineralisation? Describe how it happens.
The infilling of voids and spaces by minerals. Dissolved minerals (groundwater in terrestrial setting) infiltrate voids and pores inside plant tissue - infills cells as cell contents decay more rapidly than cell walls - cell walls may persist as carbon (residues of organic tissues) - silification is popular mode of preservation of unicellular organisms - calcite (coal balls) - pyrite (iron sulphide)
What is the main difference between perimineralisation and petrifaction?
In perimineralisation the cell walls are preserved while in petrifaction the cell walls are replaced
What occurs in petrifaction?
It involves the replacement of tissues by minerals.
Typically the cell walls are replaced as well as any spaces being infilled (interior of cells).
Give 2 examples of petrifaction.
1) petrified grass stem from medieval cess pit in Kilkenny -cell interiors infilled with calcium phosphate and cell walls replaced by calcium phosphate
2) Rhynie Chert: Scotland, petrified plant and animal community, 400mya, an exceptional window into biosphere.
