What is Paleobotany?


Paleobotany is a field of paleontology that studies plants throughout geologic history, and is primarily concerned with the fossil record and evolutionary history of plants.

Objectives of paleobotany
  • The major aim is to reconstruct entire fossil plants 
  • To assign extinct plants to particular taxonomic groups
  • To understand evolution of extinct (fossil) plants
What is a fossil? 
  • Any evidence of previous life
  • Either direct or indirect evidence
  • Fossil localities exist from the Arctic through the tropics into Antarctica 
  • In sedimentary rock; usually in places where these rocks have been exposed 
    • e.g. eroded cliffs, road cuts, quarries, mines, etc.
Direct Fossil Evidence
    • Material from past organisms in its original, or sometimes altered form 
    • Direct evidence can provide information about… 
      • morphology: the external form of an organism 
      • anatomy: internal cellular structure 
      • ultrastructure: subcellular structure
Indirect Fossil Evidence
    • Chemical fossils or chemofossils
    organic signatures of past life
    • Imprints made by an organism
      • Impressions of plant parts
      • Ichnofossils or trace fossils 
      • Footprints
Above
: impression fossil of palm leaf
Below: trace fossil of Cambrian invertebrate
    • Products of the organism's metabolism 
      • amber: resins produced by trees 
      • coprolites: waste products of animals 
Above: coprolite of dinosaur
Below: fossil amber with some inclusions
    • Indirect evidence can provide information about… 
      • evidence of presence
      • behavior (e.g. community living) 
      • ecology (e.g. predation/defense)
      • physiology (e.g. running speed) 
Conditions of Fossilization
  1. Removing the material from oxygen-rich environment of aerobic decay 
  2. "Fixing" the organic material to retard anaerobic decay 
  3. Introducing the fossil to the sedimentary rock record
Types of Fossilization
  • Compressions: 2-dimensional, with organic material
    • Physical deformation such that the 3-D structure is compressed to more-or-less two-dimensions
    • Compressions retain organic matter, usually more or less coalified
    • Peat, lignite, and coal are essentially compressions of thick accumulations of plant debris relatively free of encasing mineral sediment
Above: compression of fern leaf
  • Impressions: 2-dimensional imprints, devoid of organic matter
    • Impressions are essentially compressions sans organic material. If the sediment is very fine-grained, impressions may faithfully replicate remarkable details of original external form, regardless of subsequent consolidation of the sediment
    • Most commonly found in fine-grained sediment such as silt or clay
Above: 
impression of palm leaf
  • Casts / Molds3-dimensional, may have a surface layer of organic material
    • A cast results when sediment is deposited into cavities left by the decay of plant parts
    • A mold is essentially a cavity left in the sediment by the decayed plant tissue. Molds are generally unfilled, or may be partially filled with sediment
    • Casts and molds commonly lack organic matter, but a resistant structure may be preserved as a compression on the outside of the cast or the inside of a mold
    • Casts and molds may be found together with the cast filling the mold
Above: cast stump of Eospermatopteris
  • Permineralizations: 3-dimensional, tissue infiltrated by minerals allowing internal preservation
    • Permineralization occurs when the plant tissues are infiltrated with mineral-rich fluid
    • Minerals precipitate in cell lumens and intercellular spaces, thus preserving internal structures of plant parts in three dimensions
Above: permineralized stump from Petrified Forest National Park
  • Molecular Fossils non-structural, preserves organic compounds
    • Breakdown products of chlorophylls and lignin have been found in well-preserved fossil leaves. 
    • Lipids and their derivatives have also been recovered from sediments. 
    • Some carbohydrate break-down products may also survive in sediment. 
    • Genetic material was recovered from Tertiary leaves, and the age of material from which DNA and RNA is recovered seems to be greater with every issue of Nature.
Subdisciplines of Paleobotany
  • Biostratigraphy 
  • Development / Growth of ancient organisms 
  • Form and function of plant structures 
  • Interrelationships of organisms & environment 
  • Origin and evolution of major plant groups 
    • Evolutionary patterns of taxa 
    • Macroevolution and speciation/extinction
  • Paleoclimate 
Form Genera 
  • Disarticulation of plant structures during fossilization creates problems with taxonomy 
  • Paleobotanists attempt to find evidence to connect plant parts
    • roots to stems to leaves
    • stems to reproductive structures (flowers, fruits, sporangia)
    • seeds and spores to fruits and sporangia, respectively
  • This problem is rectified by assigning a taxonomic name, a form genus, to each dis-articulated plant structure 
    • leaves, stems, roots, sporangia, spores, pollen, seeds, bark, etc. may all receive separate taxonomic names
  • Example: Carboniferous Scale Tree
    • Lepidodendron: upright stem with bark
    • Lepidophylloides: leaves (microphylls) 
    • Stigmaria: root-like rhizophore (modified rhizome-like stem that anchors and absorbs water/minerals)
    • Lepidostrobophyllum: sporophyll (leaf protecting sporangia)
    • Lepidocarpon: female cone (contains megaspores) 
    • Cystosporites: megaspores, which will produce female gametophytes
    • Lepidostrobus: male cones (contains microspores) 
    • Lycospora: microspore, which will produce male gametophytes

Cladistics (from Botany 317): methodology to deciphering true evolutionary groupings

Paleontology is a historical science
  • Modern computing had allowed for the introduction of experimental science to the field of paleontology
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