Paleobotany, also spelled as
palaeobotany (from the
Greek words
paleon = old and "
botany", study of plants), is the branch of
paleontology or
paleobiology dealing with the recovery and identification of
plant remains from
geological contexts, and their use for the
biological reconstruction of
past environments, and the
evolution of both the
plant kingdom and
life in general. A synonym is
paleophytology. Paleobotany includes the study of
terrestrial plant fossils, as well as the study of
prehistoric marine photoautotrophs, such as
photosynthetic algae,
seaweeds or
kelp. A closely-related field is
palynology, which is the study of
fossilized and
extant spores and
pollen.
Paleobotany is important in the reconstruction of ancient
ecological systems and
climate, known as
paleoecology and
paleoclimatology respectively; and is fundamental to the study of green
plant development and
evolution. Paleobotany has also become important to the field of
archaeology, primarily for the use of
phytoliths in
relative dating and in
paleoethnobotany,
Overview of the paleobotanical record
Macroscopic remains of true
vascular plants are first found in the
fossil record during the
Silurian Period of the
Paleozoic era. Some dispersed, fragmentary fossils of disputed affinity, primarily
spores and
cuticles, have been found in rocks from the
Ordovician Period in
Oman, and are thought to derive from
liverwort- or
moss-grade fossil plants (Wellman et al., 2003).
An important early land plant fossil locality is the
Rhynie Chert, an Early
Devonian sinter (
hot spring) deposit composed primarily of
silica found outside the town of
Rhynie in
Scotland.
An unpolished hand sample of the Lower Devonian Rhynie Chert from Scotland.
The Rhynie Chert is exceptional due to its preservation of several different clades of plants, from
mosses and
lycopods to more unusual, problematic forms. Many fossil animals, including
arthropods and
arachnids, are also found in the Rhynie Chert, and it offers a unique window on the history of early terrestrial life.
Plant-derived
macrofossils become abundant in the Late
Devonian and include
tree trunks,
fronds, and
roots. The earliest tree is
Archaeopteris, which bears simple,
fern-like
leaves spirally arranged on branches atop a
conifer-like
trunk (Meyer-Berthaud et al., 1999).
Widespread
coal swamp deposits across North America and Europe during the
Carboniferous Period contain a wealth of fossils containing
arborescent lycopods up to 30 meters tall, abundant
seed plants, such as
conifers and
seed ferns, and countless smaller,
herbaceous plants.
Angiosperms (
flowering plants) evolved during the
Mesozoic, and flowering plant pollen and leaves first appear during the Early
Cretaceous, approximately 130 million years ago.
Plant fossils
A
plant fossil is any preserved part of a
plant that has long since died. Such fossils may be prehistoric impressions that are many millions of years old, or bits of charcoal that are only a few hundred years old. Prehistoric plants are various groups of
plants that lived before recorded
history (before about
3500 BC).
Kinds of plant fossils
A
fossil Viburnum lesquereuxii leaf with insect damage; Dakota Sandstone (
Cretaceous) of Ellsworth County, Kansas. Scale bar is 10 mm.
One of the most common kinds of plant fossils is a
compression fossil, in which a leaf or flattened part of the plant has been pressed between layers of sediment and often preserved as a
carbonaceous film. Also common are fossil
pollen and
spores from ancient lake beds, as well as
charcoal. Less common, but economically more important, is
coal from the plants of
Carboniferous swamps.
One of the most spectacular of plant fossils is
petrified wood.
Form taxa
Fossils of plants are very different from the fossils of
animals, and this is in part a result of the different architecture of plants. Animals develop with specific parts, and in both the young and adult animal, those parts exist in fixed numbers and locations. Even animals which undergo
metamorphosis have only one head, and will emerge with a fixed body structure. By contrast, plants are continually producing new branches, leaves, and other parts throughout their lives. These parts may fall off without injuring the plant. Thus, plants fossils are often fragmentary pieces such as leaves, branches, or pollen.
Since a leaf, stem, spore, or seed may be found preserved without any physical connection to the plant from which it came, paleobotanists use
form taxa (singular
form taxon) to name and classify such fossils. When the true identity of such fossils is later discovered, the two form taxa may be merged. For example, in the 1960s fossil leaves called
Archaeopteris (literally "ancient fern") were found attached to fossil wood of the tree
Callixylon. The whole plant is now known to be a
Devonian tree with
fern-like leaves but with
gymnosperm-like
wood.
Some form taxa continue to exist even after their identity is determined. This is a matter of convenience for identifying quickly which part was found as a fossil, especially which the fossil may come from more than one kind of plant. Leaves assigned to the form taxon
Sphenopteris come from both ferns and from seed plants; it usually is not possible to determine from isolated fossils which group the leaves belong to.
Fossil groups of plants
Some plants have remained remarkedly unchanged throughout earth's geological time scale. Early
ferns had developed by the
Mississippian,
conifers by the
Pennsylvanian. Some plants of prehistory are the same ones around today and are thus
living fossils, such as
Ginkgo biloba and
Sciadopitys verticillata. Other plants have changed radically, or have gone extinct entirely.
A few examples of prehistoric plants are:
See also
Notable Paleobotanists
