1.4 - The Fossilisation of Plants

Question 1

What are plants? Describe their biology and what is good/bad about it.

Answer 1

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).

Question 2

What are the two types of land plants?

Answer 2

Vascular and non-vascular

Question 3

What are non-vascular plants also known as? Give 3 examples of non-vascular plants.

Answer 3

Also known as bryophytes.

Eg. liverwort, hornworts, mosses

Question 4

What can vascular plants be subdivided into?

Answer 4

Seedless and Seed plants

Question 5

Give 3 examples of seedless plants.

Answer 5

Club mosses, ferns, horsetails

Question 6

What can seed vascular plants be subdivided into?

Answer 6

Gymnosperms and Angiosperms

Question 7

What is an angiosperm?

Answer 7

All flowering plants - the seeds are enclosed within an ovary (usually a fruit)

Question 8

What is a gymnosperm?

Answer 8

No flowers or fruits - enclosed/naked seed on surface of scales/leaves - often seeds confined as cones

Question 9

Why is there bias in the preservation of vascular and non-vasular plants? Give an example

Answer 9

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)

Question 10

What is the function of xylem?

Answer 10

Conducts water and disolved nutrients upwards

Question 11

What is the function of phloem?

Answer 11

Conducts photocynthetic products (sugars) downwards

Question 12

What is the key thing about vascular tissues that gives them more recalcitrance than non-vascular plants?

Answer 12

Their cell walls are made of cellulose which gives rigidity in life and recalcitrance after death

Question 13

Why are bryophytes (non-vascular plants) less recalcitrant?

Answer 13

They never form xylem tissue

Question 14

What are phytoliths?

Answer 14

microscopic mineralised bodies (silica) in plant cells - they form as a defence against being browsed upon

Question 15

What are plant propagules?

Answer 15

spores in non-vascular and some vascular plants - seeds and pollen in vascular plants - decay resistant biomolecules - good preservation potential

Question 16

How are plant propagules often transported?

Answer 16

By wind so are often on surface of plant - this is why resistant biomolecules which helps preservation potential

Question 17

What are the 6 modes of preservation for plants?

Answer 17

3D remains, Compression, Charcoalification, Casts of stems and roots, perimineralisation, petrifaction

Question 18

What are 3Dremains common for?

Answer 18

Pollen and spores

Question 19

What occurs in compression?

Answer 19

Carbon films (2D - flattened and preserved as carbon) can retain ultrastructure - they create an impression (in counterpart)

Question 20

What occurs in charcoalification?

Answer 20

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)

Question 21

What occurs to create casts of stems and roots?

Answer 21

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).

Question 22

What is perimineralisation? Describe how it happens.

Answer 22

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)

Question 23

What is the main difference between perimineralisation and petrifaction?

Answer 23

In perimineralisation the cell walls are preserved while in petrifaction the cell walls are replaced

Question 24

What occurs in petrifaction?

Answer 24

It involves the replacement of tissues by minerals.

Typically the cell walls are replaced as well as any spaces being infilled (interior of cells).

Question 25

Give 2 examples of petrifaction.

Answer 25

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.