Nomenclature of Fossils

The whole plant is not preserved, but only detached plant parts like stem, root, cone, leaf, etc. are preserved as fossils. These detached plant parts are being discovered in different times by different authors. Thus, the detached plant parts or organs are given name on the basis of Binomial Nomenclature (“generic and specific name”) acc.to rules of International Code of Botanical Nomenclature which have been framed for living plants.

The first valid description of Lepidodendron came into existence from the publication of Sternberg in 1820. Thus, this date has been considered as the starting point of palaeobotanical nomenclature.

Each detached organs or fragments is given a different name. Each of these names acquires the status of a genus. The generic name in fossils is applicable for only a plant part like root, stem, leaf, cone or other organ, without indicating to what plant is belongs. Thus, the genus is termed form genus or artificial genus in contrast to natural genus for living plants. A form genus cannot reliably be assigned to a single family; however, it may be assigned to an order or other higher taxonomical rank. For example, Stigmaria is a form genus of the order Lepidodendrales which cannot be assigned to any one of the three families: Lepidodendraceae, Sigillariaceae or Bothrodendraceae.

When the relationships among different organs like stem, root, leaf and reproductive structures are established and can be assigned to the same family, then the genera can be called organ genera. For example, stem genus Bucklandia, leaf genus Ptilophyllum, male fructification Weltrichia and female fructification Williamsonia are genetically related and assigned to the same family Williamsoniaceae. Thus, all are considered to be organ genera. However, there is no provision in the international rules of botanical nomenclature for the use of organ genera.

During reconstruction the palaeobotanists should select the earliest (after 1820) validly published generic name applied to ay one of its parts as per rule of priority. He or she will use any one of the form genera as the generic name for the whole organism.

Rules for naming form genera

A particular suffix is used for naming a form genus which signifies the organ it belongs. The suffixes applied to different plant parts are as fo0llows:

Suffix Applied to organ Examples Dendron Stem Lepidodendron, Lyginodendron Xylon Woody part Dadoxylon, Cardaixylon, Mesoxylon Phyllum Leaf Ptilophyllum, Nipaniophyllum, Brachyphyllum Pteris Fern like stem or frond Sphenopteris, Lyginopteris, Etapteris, Archaeopteris. Spermum Seed Corystospermum, Mitrospermum Carpon Seed or seed like Lepidocarpon, Mazocarpon, Calamocarpon Carpus Seed Trigonocarpus, Cardiocarpus Stoma Seed Lagenostoma, Stamnostoma Theca Microsporangia Codonotheca, Aulacotheca, Crossotheca Strobus Cone Lepidostrobus, Androstrobus.

Significance of studying fossils plants Palaeobotany is a branch of plant science which deals with the study of plant fossils. The various objectives of palaeobotany are:

Basic aspect

Such studies help us to understand the past vegetation, climate and palaeoecology including the history of plant evolution, biostratigraphy, etc. Some of the important basic aspects of such application are:

(a) To decipher palaeovegetation and paleoclimate: plant fossils serve as tool for past vegetational studies.

A correlation exists between fossil plants and their surrounding environments From remote geological past which serve as an index for palaeoclimate. The fossil plants are used for understanding the past climate, because the present-day living plants are well understood for their integral association with the idea ‘present is the key to the past’.

(b) Provide evidence for origin and evolution of plants: The study of fossil plants plays an important role in understanding the origin and evolution of different plant groups through ages. A most dramatic event took place in the history of plant life i.e. the evolution of land plants during Silurian period. For transition of plants from aquatic habit to terrestrial habit the plants needed to be self-supportive and they had to be able to withstand the drying effect of the atmosphere leading to a series of adaptations. Such adaptations were -development of cuticle in their outer surface to check desiccation, -formation of roots as anchoring and absorptive organ, - stomata for gaseous exchange, vascular tissue for conduction. Thus, during Silurian Devonian periods more and increasingly complex fossils plants represented by Rhyniopsida appeared with such adaptive features. (c) To ascertain palaeophytogeography: The important aspect of studying palaeobotany is to ascertain the palaeophytogeographic condition. The most astonishing example of such aspect is the concept of Gondwanaland, which consisted of a single land mass formed by the union of the faraway continents of the Southern Hemisphere, such as South America, South Africa, Madagascar, Australia, New Zealand. Antarctica and India. The fossils evidence shows a clear floral continuity ranging in age from the upper carboniferous to the beginning of the cretaceous. (d) To make biostratigraphic correlation:The study of fossils plants has an applied significance in understanding the biostratigraphical sequence which provides evidence to trace the plant evolution through ages. (e) Calculation of age of the rocks: Radioactive elements are generally used for dating the rocks. But sometimes, index fossils are used to date a rock of unknown origin.

Applied aspect

To provide useful information in the exploration of fossil fuel like coal and oil:

The plant inhabitants of Palaeozoic Mesozoic swamps served as source of coal and formed coal seams. Accumulation of plants materials with a variety of minerals coupled with mud, slit and other organic materials constitute a coal bed. Many plant parts get beautifully preserved as fossils in the stratified sedimentary layers which are closely adjacent to coal layers.

A stratified scale based on fossils can be made to establish the age of coal deposits and their position in the succession of rocks. Palaeobotanical studies have served as a tool to ascertain age of coal layers, their lateral extent and quality of coal deposits. Such information is required to specify the suitability of a particular coal for energy production.

The assemblage of fossil pollen grains and spores has contributed significantly in the field of oil exploration. The problem of oil exploration begins with search of oil reservoirs. Exploration of oil is done by (i) Determining the thermal alteration index. (ii) Palynostratigraphy (iii) Defining of ancient shorelines.