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a branch of botany dealing with fossil plants. It includes the study and classification of plants of the geological past, as well as the study of their relationship with each other and with extant plants. Paleobotanists seek to establish the distribution of various plants during different geological periods and to understand the principles governing changes in plant cover. Paleobotany and paleozoology are usually joined in the science of paleontology.
Principal approaches and methods. The taxonomy of fossil plants, or taxonomic paleobotany, is based on the same principles as the taxonomy of extant plants. It does, however, have a number of special features. Most plant fossils are disconnected remains of plants whose membership in the same taxon cannot always be proved. The remains, therefore, are often given different specific and generic names. Uniting dissociated remains of plants under the same name is possible only when there is proof of their organic connection.
The tasks of morphological paleobotany consist in elucidating the external and internal structures of plants of the geological past and reconstructing their appearance. Morphological paleobotany provides important data for taxonomic paleobotany, paleofloristics, and paleoecology. The data serve as the foundation for elucidating the history of certain taxons and the evolution of the plant kingdom as a whole. In addition, the information is valuable for constructing a phylogenetic system of the plant world. Paleofloristics, the comparative study of the floras of the geological past, yields valuable information for stratigraphy and paleogeographic reconstruction.
Plant paleoecology is concerned with the conditions under which plants and their communities existed in the geological past. Paleoecological research is based on morphological features of fossil plants, the aggregate of buried plant remains (taphocenosis), and the structure of the burials themselves.
The boundaries between these three principal approaches of paleobotany are to a large extent conventional. A paleobotanist studyingthe flora of a certain period usually investigates simultaneously the taxonomy, morphology, and ecology of fossil plants.
Paleobotany is divided into several disciplines. Each discipline deals with a specific type of remain (leaf, fruit, seed, wood, spore, pollen grain) or a specific form of preservation (compression fossils, petrifactions, impressions). Compression plant fossils are mummified remains that have been altered somewhat and are sometimes slightly mineralized. Petrifactions are fossils in which the original plant tissue is replaced by mineral matter. Impressions are the imprints of leaves or other plant organs. They are usually accompanied by remains of the plant itself, which are preserved as a compression fossil or a distinctive flat petrifaction.
The name “ichnophytology” has been proposed for the division of paleobotany that studies the impressions and, less frequently, the remains of leaves, stems, and other parts of plants. Paleostomatography is concerned with the epidermis, especially the stomatal apertures, of the leaves and other organs of fossil plants. Paleocarpology deals with fossil fruits, seeds, and mega-spores. Paleopalynology is concerned with investigating fossil spores and pollens. Paleoxylology is the study of fossil wood.
Paleomycology and paleoalgology have been separated into independent disciplines. The study of planktonic forms of fossil algae is acquiring ever greater stratigraphic significance. The investigation of the most ancient bacteria, Cyanea, and algae is very important for an understanding of the earliest stages of development of the organic world.
Principal stages of development. Remains of fossil plants in the form of petrified wood chips, leaf impressions, and amber have been described since ancient times. In the sixth and fifth centuries B.C., Xenophanes wrote that “laurel leaves” had been found in rocks on the island of Paros. However, leaf impressions and other traces and remains of ancient plants were interpreted for a long time as a fluke of nature. Leonardo da Vinci and scientists of his day identified these formations as remains of plants that existed at one time, but they had no idea how old they were.
In the late 17th and 18th centuries, scientists primarily concentrated on identifying fossil plants by comparing them with living plants. They sought to classify the various types of plant remains. What seems to have been the first detailed classification of fossil plants was published in London in 1699 by E. Llywd. In the 18th century the German paleobotanists G. Volkman, G. Knorr, and J. Walch published several monographs with descriptions and illustrations of fossil plants. However, the first attempts at periodization had to await the introduction of the paleontological method in stratigraphy by the British botanist W. Smith at the turn of the 19th century. The taxonomy of fossil plants was begun by the German paleobotanist E. von Schlotheim (1804), who was the first to apply Linnaeus’ binary system to fossil plants. The Czech paleobotanist C. Sternberg (1820–38) and the French biologist A.-T. Brongniart (1822–38), working from the assumption that the various classes of plants had different degrees of antiquity, proposed the division of the history of the plant world into three and four periods, respectively. They thereby laid the foundation for the future phytogeny of plants. Great contributions to the taxonomy of fossil plants were made by the English botanists J. Lindley and W. Hutton (1831–37), the German paleobotanist H. Goeppert (1836–45), the German mycologist-paleobotanist A. Corda (1845), and the Austrian botanist F. Unger (1845). In Russia some descriptions of fossil plants were published in the 18th century. Of special importance was the work of la. G. Zembnitskii (1825–33), in which methods of paleobotany were set forth and a survey of all fossil plants known at that time was given. The first finds of fossil plants were predominantly in Europe. In the middle of the 19th century, besides detailed descriptions of European flora of all periods, investigations of the floras of polar regions, North America, India, and Australia were begun. The descriptive works of that period, which are associated with Goeppert, Unger, the Swiss paleobotanist O. Heer, the Austrian botanist C. von Ettings-hausen, the French botanist G. de Saporta, and the American geologist J. Newberry, retain their importance to this day. In Russia the most important paleobotanical research of the mid-19th century was conducted by E. I. Eikhval’d, K. E. Merklin, and I. F. Shmal’gauzen.
At this stage in the development of paleobotany, the history of the plant world was divided into seven periods (Unger, 1852). Subsequent elaboration of the geochronological scale and progress in the study of the floras of all geological periods led to the formulation of theoretical generalizations at the end of the 19th century, including those by A. Engler (1879–82) and R. Zeiller.
At the beginning of the 20th century there were new developments in paleobotany. A number of new disciplines arose, including paleopalynology and paleocarpology. Old research methods were improved, and new ones appeared. In 1903 the English paleobotanist D. Scott discovered a group of seed ferns. In 1911 the Russian paleobotanist M. D. Zalesskii discovered Callixylon wood from the Devonian; its structure was similar to that of wood from gymnosperms. In 1925 the British scientist H. Thomas discovered Caytoniales. Comprehensive studies were carried out on Rhynia (British scientists R. Kidston and W. Lang, 1917–21), the subclass Primofilices (Lang, 1926; the German botanists R. Kräusel and H. Weyland, 1933), and the strobiles of Cordaianthus and ancient conifers (Swedish botanist R. Florin, 1944–51). These discoveries, studies, and other works of morphological-taxonomic character made possible the formulation of an accurate picture of the evolution of morphological structures and led to important generalizations concerning plant morphology and phytogeny. Such generalizations were formulated by the English botanist C. Jeffrey (1917); the German botanists W. Zimmermann (1930, 1959), F. Bower (1935), and A. Eames (1936); and the Soviet botanist A. L. Takhtadzhian (1956).
The organic connection between the wood of Callixylon and the foliage of Archaeopteris, typical of ferns, was proved by the American paleobotanist C. Beck in 1960. Beck’s evidence and the detailed study of psilophytes by the Americans H. Banks and F. Hueber (1968) led to the reexamination of several traditional ideas concerning the evolutionary relationships among ancient groups of higher plants (Beck, 1960–62; T. Delevoryas, 1962; Banks, 1970; D. Bierhorst, 1971).
In the 1930’s and 1940’s the foundation was laid for broad paleophytogeographic generalizations by the German paleobotanist W. Gothan, the Britain botanist A. Seward, and such Soviet paleobotanists as A. N. Krishtofovich, V. D. Prinada, and M. F. Neiburg. Important research devoted to problems of paleophytogeography was conducted by the American paleobotanist D. Axelrod (1958); the Soviet botanists V. A. Vakhrameev (1964, 1970), Takhtadzhian (1966), and S. V. Meien (1970, 1973); and the British botanist W. Chaloner (1973). The scientific and organizational activity of Krishtofovich, who, in addition to studying numerous paleofloras from the Devonian to the Quaternary, elaborated a number of important theoretical problems, were of great significance in the development of paleobotany in the USSR.
At present, paleobotany is characterized by the progressive specialization and integration of its disciplines. This is due to the new multilateral theoretical approach to the solution of a number of general theoretical and practical problems of biology and geology. Paleobotanical data and data from related disciplines are correlated, and new methods of research (anatomical, cyto-logical, biochemical, mathematical, experimental) are continually being introduced. In addition, the most up-to-date equipment, including raying and scanning electron microscopes, is used.
A number of phytogeographic concepts and paleogeographic and paleoclimatic reconstructions have been reexamined owing to the comprehensive worldwide revision of certain taxons of fossil plants and of paleofloras of all periods and to the ecological approach to their interpretation. In addition, a more accurate periodization of the history of the plant world as a whole has been formulated.
Leading paleobotanical laboratories of the USSR. The first scientific collection of fossil plants was gathered in 1830 at the St. Petersburg Botanical Garden (now the V. L. Komarov Botanical Institute). Here in 1932, I. V. Palibin organized the first paleobotanical laboratory. Since the late 19th century, paleobotanical research has been conducted at the Geological Committee (now the All-Union Scientific Research Geological Institute). Such research was initiated in the late 1920’s at the Geological Institute of the Academy of Sciences of the USSR and in the 1930’s at the All-Union Geological Oil Exploration Institute in Leningrad and at the Institute of Geological Sciences of the Ukrainian SSR. Paleobotanical laboratories or small groups of paleobotanists are found at a number of botanical and geological institutions in Moldavia, Georgia, Armenia, Azerbaijan, Kazakhstan, Uzbekistan, and other Union republics. Such institutions are located in Kazan, Novosibirsk, Tomsk, Vladivostok, and other cities.
International organizations. The International Organization of Paleobotany is part of the International Union of Biological Sciences. At the Third International Palynological Conference in Novosibirsk in 1971, the International Palynological Committee was founded, some of whose members are concerned with paleopalynology. The All-Union Botanical Society and the All-Union Paleontological Society have paleobotanical sections.
Periodicals. Articles on paleobotany appear in Botanicheskii zhurnal SSSR (Botanical Journal of the USSR; published since 1916), Paleontologicheskii zhurnal (Paleontological Journal; since 1959), and various geological and general scientific periodicals. International journals dealing with paleobotany include Palaeontographica. Abt. B. Palaeophytologie (Stuttgart; since 1846), The Palaeobotanist (Lucknow; since 1952), and Review of Palaeobotany and Palynology (Amsterdam; since 1967).
REFERENCESSeward, A. C. Veka i rasteniia: Obzor rastitel’nosti proshlykh geologiches-kikh periodov. Leningrad-Moscow, 1936. (Translated from English.)
Takhtadzhian, A. L. Vysshie rasteniia, vol. 1. Moscow-Leningrad, 1956.
Krishtofovich, A. N. Istoriia paleobotaniki v SSSR. Leningrad, 1956.
Krishtofovich, A. N. Paleobotanika, 4th ed. Leningrad, 1957.
Osnovy paleontologii: Vodorosli, mokhoobraznye, psilofitovye, plaunovidnye, chlenisto-stebel’nye, paporotniki. Moscow, 1963.
Osnovy paleontologii: Golosemennye i pokrytosemennye. Moscow, 1963.
Paleopalinologiia, vols. 1–3. Leningrad, 1966.
Paleozoiskie i mezozoiskie flory Evrazii i fitogeografiia etogo vremeni. Moscow, 1970. (Trudy Geologicheskogo instituta AN SSSR, issue 208.)
Krasilov, V. A. Paleoekologiia nazemnykh rastenii (Osnovnye printsipy i melody). Vladivostok, 1972.
Iskopaemye tsvetkovye rasteniia SSSR, vol. 1. Leningrad. (In press.)
Andrews, H. N. Studies in Palaeobotany. New York-London, 1961.
Delevoryas, T. Morphology and Evolution of Fossil Plants New York, 1962.
Gothan, W., and H. Weyland. Lehrbuch der Paldobotanik, 2nd ed. Berlin, 1964.
Mägdefrau, K. Paläobiologie der Pflanzen, 4th ed. Jena, 1968.
Němejc, F. Paleobotanika, vols. 1–3. Prague, 1959–68.
Traité de paleobotanique, vols. 2–4 (fasc. 1). Published under the direction of E. Boureau. Paris, 1967–70.
Bierhorst, D. W. Morphology of Vascular Plants. New York-London, 1971.
S. G. ZHILIN and N. S. SNIGIREVSKAIA; under the general editorship of A. L. TAKHTADZHIAN